Soviet Union (1941)
Heavy Tank – 1 Partial Prototype + 1 Mock-up Built
Right after the trials of the T-150 and KV-220 heavy tanks, trial reports on the anti-tank capabilities of high caliber German anti-aircraft guns and German heavy tank developments kickstarted the development of even more powerful heavy tanks. One of these was the KV-3, which used a slightly modified version of the KV-220 hull, but with an all new turret, armed with the new, powerful 107 mm ZiS-6 gun. Despite these features, several delays regarding the production of the first prototype and the invasion of the Soviet Union halted the progress to the point that the project was no longer needed.
The KV-1 entered production in the summer of 1941 at the Leningrad Kirov Plant (LKZ). In parallel, the plant was tasked with further developing the KV-1 to fit larger guns and thicker armor. The products were the T-150, T-220 and T-221. While the first was essentially a KV-1 with 90 mm of armor, the latter two featured new, lengthened hulls. The T-220, also known as the KV-220, had 100 mm of armor and was equipped with an 85 mm F-30 gun. The first prototype was completed on 7 December 1940, and tested in January the following year.
The SKB-2 design bureau, where the KV tanks were developed, had juggled with the idea of installing a 107 mm gun in a tank since August 1940. Engineer G.N. Moskvin was tasked with researching the fitting of a 107 mm gun inside the KV-220 turret. The gun would turn out to be the 107 mm F-42, developed by December of the same year, and later indexed ZiS-6.
Initial calculations revealed that fitting the F-42 gun in the KV-220 turret would have been nearly impossible, the cramped room and very long shells would have made loading impossible and the idea was dropped. The 107 mm gun reappeared in the picture when preparing the second KV-220 prototype. On 19 February, Marshal Kulik, overseeing work at LKZ, wrote a letter where he claimed that the second prototype was to be armed with the ZiS-6. However, physical work on this prototype did not start until June 1941.
The trials of both the KV-150 and KV-220 ended in late January due to serious engine failures, causing both tanks’ development process to be halted until Plant No.75 fixed their engines. The completion of the KV-220 was further delayed when, on 11 March 1941, the Soviet intelligence services sent a letter discussing German tank development. Most importantly, three German tanks were claimed to be under development, the 36-tonne Ausf.V armed with a 75 mm gun and 60 mm of armor, the 45-tonne Ausf.VI armed with a 75 mm gun and 70 mm armor and finally, the 90-tonne Ausf.VII with a 105 mm gun.
At the time, the only heavy tanks which the Soviets had in service were the horrendously obsolete T-35A and the new KV-1, which was apparently no match for the supposed super heavy German tank. Even the heavy tanks under development were no match. The T-150 had been canceled after the failed trials and replaced by the Object 222, essentially the same tank with a more streamlined turret and armed with the 76 mm F-34. This was also the first tank to be called KV-3. Additionally, the KV-220, while promising, still was not powerful enough to face the 90 tonne German tank.
Another issue which catalyzed the development of heavier tanks came from the trials of German 88 and 105 mm anti-aircraft guns by the Soviets, concluding that tanks needed 130 mm or more of armor that was specially treated at high-frequencies.
Thus, on 21 March, the Soviet GABTU (Main Directorate of Armored Forces) laid down the requirements for SKB-2 to develop a 72 tonne tank, armed with the ZiS-6 gun, which was called the KV-4, later given index Object 224.
On 26 March, 1st Rank Military Engineer Afonin sent a report to the GABTU regarding armor thickness and the issues caused by German anti-aircraft guns, leading the GABTU to cancel the Object 222, which was deemed inadequately armored.
Shortly after, on 7 April, the Council of People’s Commissars of the Soviet Union requested two additional tanks. One was to be the new KV-3 (the Object 222 was thus renamed to KV-6), weighing 68 tonnes, and the other the KV-5, weighing 100 tonnes. Much like the KV-4, both of these tanks were to be armed with the same 107 mm ZiS-6 gun.
Just two days later, on 9 April, the People’s Commissariat of Heavy Machinery expanded on the previous decree, and the technical requirements were laid down. The frontal armor was to be 115-120 mm thick, turret armor 115 mm, and be equipped with the 107 mm ZiS-6 gun with 800 m/s muzzle velocity. Deadlines were also extremely tight. By 15 April, the drawings had to be ready and submitted to the Izhora plant. The first turret mock-up was meant to be ready by 25 April and the first full prototype by 20 May.
It is important to note that, while 120 mm of armor was less than the estimate of 130 mm to withstand the future German tank guns, it was deemed enough to protect against the 88 mm gun. Instead, the KV-4 had its frontal armor thickness set to 130 mm and the KV-5 to 170 mm.
The KV-3 received index Object 223, and was to use the slightly altered hull of the KV-220 in order to simplify and speed up development. The only difference was that the frontal armor had to be thickened to 115 mm and a new turret had to be developed to accommodate the larger gun, as well as fitting 120 mm of frontal armor. The powerplant was meant to be the same 850 hp V-2SN supercharged diesel as on the KV-220. Work on the tank began in mid-April at SKB-2, with the chief engineer being L.E. Sychev, who was later replaced by B.P. Pavlov, though some sources contradict whether this swap was made when designing the KV-220 or KV-3. Work on the first mock-up used the hull of the T-221, work on which had begun earlier in February. Essentially an identical hull to that of the KV-220, the only change was the thickening of the frontal armor plates by 15 mm, to a total of 115 mm.
However, due to the problems of the V-2SN engine highlighted at the KV-220 trials, and until it was ready for production, the KV-3 would use a V-5, 700 hp engine. An experiment was made by loading the KV-220 hull up to a total mass of 70 tonnes and using the V-5 engine. The torsion bars were sagging by 2-3 cm, and between 12-15 April, the vehicle drove 150 km. Although the V-5 was deemed satisfactory on roads, on rough terrain, the tank could only be driven in 2nd gear. Another issue spotted with the engine was that it would eject hot oil through the cooling grille.
On 18 April, 2nd Rank Military Engineer Bubyakin reported to the GABTU that the KV-3 mock-up would be based on the T-221 hull and that there were plans to strengthen the side armor depending on the circumstances. By 26 April, the KV-3 mock-up was ready and, on 7 May, an inspection was made by a state commission, consisting of representatives from GABTU, People’s Commissariat of Heavy Engineering and LKZ. Several comments were submitted and changes had to be made. The bow 7.62 mm DT machine gun was recommended to be replaced with a flamethrower on some units. Other changes mostly involved the ZiS-6 gun. An internal travel lock, a gun rammer and single-piece ammunition were requested. Several structural and design changes were also proposed, especially regarding the turret.
When it came to building the first prototype, several problems delayed the project. On 13 May, senior representative of the GABTU, Military Engineer 2nd Rank Dmitrusenko, claimed that the Izhora plant would, ideally, manufacture the stamped turret by 20 May. However, for this process, two dies and two punches were needed, but as of that day, the second die was still to be cast. Additionally, none of these components were heat treated and machined, which would have taken a few extra days. In his own words, Dmitrusenko wrote:
“There is a chance that by 20 May, the dies and punches will not be ready, let alone the turret itself. Unless the Izhora plant takes the most swift action in the coming days, the first turret will be manufactured no earlier than 15-20 June, exactly one month’s delay”
On 30 May, Dmitrusenko reported that the punches were being heat-treated in Shop No.15 and that the turret would be further delayed by a month.
Further trials were made on 25 May using the loaded KV-220 (reaching 65-70 tonnes) hull and V-5 engine, this time traveling 410 km. Several issues were noted, including that the axles of the return rollers were bent, idler hubs were cracked and shock absorbers on some suspension arms were sheared. While, once again, the 700 hp engine was deemed to be capable of propelling the tank at a satisfactory speed of 35 km/h, its fuel range was not considered adequate.
A delivery contract was signed on 5 June 1941, where the LKZ plant would produce 500 KV-3 tanks in the remaining months of 1941, with the first 55 units to be delivered in August, 105 in September, 110 units in October and November and lastly, 120 tanks in December.
On 27 May, the LKZ plant received a ZiS-6 gun from Plant No.92 to test the gun inside a tank. Since none of the super heavy KVs meant to equip it was ready, a KV-2 was used for firing trials instead. The gun would be mounted in the KV-2 using a KV-3 gun mantlet and mount. However, the Izhora plant once again failed to deliver the KV-3 components on time, leading to Marshal Kulik having to send a letter requesting for a speed up of the process on 18 June. By 25 June, the tank was at the Gorokhovets proving grounds, where 618 shots were fired. While penetration was deemed excellent, the gun rammer broke after 315 shots and accuracy was compromised after 486 shots. Despite these problems, the ZiS-6 was deemed satisfactory, and the gun used during the trials was sent back to Plant No.92 for repairs. By this point, the armaments plant already had 214 guns in various stages of production.
A letter from a GABTU representative at LKZ from 20 July claimed that the KV-3 prototype was still not ready and that it was expected that there would be several major issues which would be complex to solve.
By this point, the KV-3 project was getting expensive. In a letter from the head of production at LKZ, A.I. Lantsberg, the development costs estimate of the various ongoing projects at LKZ was reported.
Development cost of the KV-3 (Object 223) [in руб]
Drafts and blueprints
Models and mock-up
Technical and functional drawings
Prototype construction and factory trials
Drawing fixes/bug fixes
Prototype bug fixes and repairs
* note that the project never reached these stages, thus the project could have exceeded these allocated sums.
Start of the War
On 22 June 1941, the Axis forces began their invasion of the Soviet Union. This had an indirect effect on the heavy tank developments, as a lot of the resources had to be transferred to KV-1 production and repair. Nonetheless, work on the KV-3 and its heavier counterparts continued and several components of the first turret were finished, as well as the majority of the hull. However due to the war situation, between 26 and 30 June, an order was signed to transfer the development of the KV-3 tank to the Chelyabinsk Tractor Plant (ChTZ), alongside many of the designers. By mid-July, the KV-3 hull and other components were loaded on two rail platforms and sent from Leningrad to Chelyabisnk, with the turret being sent a little later.
On 26 July, the first of SKB-2 engineers started to arrive at ChTZ. The reasoning behind this evacuation was that the German forces were approaching the city of Leningrad. During this transfer, between July and August, the heavy KV-4 and KV-5 tanks were canceled, and work on them would not resume at ChTZ. The SKB-2 engineers in charge of the KV-3 at ChTZ were N.V. Tseits (chief engineer), B.P. Pavlov (senior engineer), G.F. Burkhanov, Merenkov, Petukh, Skortsov, Sobolev, A.S. Schneidman and N.F. Shashmurin.
Despite the fact that the KV-3 was not outright canceled, it still suffered from the transfer. Firstly, with the Siege of Leningrad beginning in September, all KV-1 production was also moved to ChTZ, leaving little resources for experimental tank work. This led to the KV-3 only appearing on various reports, letters and documents in the latter stages of 1941. Documents from September reveal that it was proposed by Plant No.92 to rearm the KV-3 with the ZiS-6A, essentially just the ZiS-6 with a 45 mm 20-K gun integrated within its system, much like on some KV-4 designs. This seems to have been more an attempt from Plant No.92 to not let their work on the ZiS-6 go to waste. Another document shows that the heavy bunker buster project, the Object 212, which was initially to be based on the KV-220, was to be built upon the KV-3 instead. On 22 December 1941, as part of the 1942 ChKZ (at the end of 1941, ChTZ was renamed to Chelyabinsk Kirov Plant) production and development plan, the KV-3 was mentioned as being in the works, with a deadline set to 1 May, 1942. Several aspects of the tank had also been reworked. By July, it was supposed to be equipped with an electrical transmission and, by December 1942, to be fitted with a 1,200 hp V-2 engine variant.
This was the last mention of the KV-3. By this point, the Soviet armored forces had suffered terrible defeats against the Axis, and were shifting focus in terms of tank design. The superior reliability and maneuverability of the T-34 caused the heavy tank industry to shift away from super heavy tanks and into the exact opposite direction, the KV-1S. With less armor than the KV-1, but with redesigned mechanical components and superior maneuverability, it was arguably the first successful Soviet heavy tank, at least from a mechanical perspective.
As the tank was based on the KV-220 hull, much of the same aspects were kept. The hull was similar to that of the KV-1, but enlarged to seven roadwheels per side, sprung by torsion bars and four return rollers. The engine and final drive were in the rear, with the sprocket. The idler was in the front. One of the main differences in the hull, aside from armor thickness, was that the engine deck was angled downwards, compared to being flat on the KV-220.
The biggest change with the new KV-3 was the new, stamped turret. Its shape was a rectangular pyramid with rounded edges. The side walls were angled at 30 degrees and extended over the hull side wall, requiring reinforcements in the hull. In the front, the large gun mantlet would house the gun and its elevation mechanism. A small protrusion was made in the left side of the turret wall to give more space for the commander and the cupola, which had six periscopes for vision. A vision port was added in the sidewall on the left side for the gunner, though it is possible that it was mirrored on the right side. In total, three firing ports were added on every side of the turret walls for firing the crew’s personal defense PPSh submachine guns. The turret ring size was 1,670 m. A service hatch was placed in the left side of the hull for use by the driver and radio operator, as well as an escape hatch in the hull floor, behind the driver’s seat.
The construction of the turret proved to be very problematic for the Izhora plant, the section of LKZ tasked with tank production. Stamped pieces of armor at 100 mm and above were a very difficult task to achieve, especially with the difficult shapes which the turret had. However, the design was a theoretical improvement over the boxy KV turret designs which the SKB-2 design bureau had made previously. In the coming years, Soviet military industrialists managed to achieve such complex armor plate shapes via casting.
The crew consisted of 6 men, namely the commander, gunner, 2x loaders, driver and radio operator. The gunner sat to the left of the gun, in the left-forward corner of the turret. The commander sat behind him, and had a large cupola for viewing the battlefield. Both of the loader’s positions were on the right side, for loading the main gun and the coaxial machine gun. The driver sat in the front of the hull, in the center, while the radio operator sat to his left. He was also responsible for operating the hull machine gun or flamethrower.
The engine was to be the 850 hp V-2SN diesel engine, developed by Plant No.75 with an AM-38 aviation supercharger and pressurization system. Fuel reserve was for 825-845 liters. However, due to the unreliability of the engine during the KV-220 trials, a 700 hp V-5 engine was used instead. The planned top speed was to be 30 km/h.
The main armament was the 107 mm ZiS-6 developed at Plant No.92 by V.G. Grabin. Praised for its good anti-tank capabilities, the gun was meant to equip the entire new line of super-heavy tanks. In total, 45 shells were stowed in the tank, within the turret and inside boxes placed longitudinally and transversely in the center of the hull, underneath the turret ring. During the trials of the gun on the KV-2, the gun could penetrate 120 mm thick armor plates angled at 30° from 1,600 meters.
Secondary armament consisted of a 7.62 mm DT machine gun mounted coaxially, to the right of the main gun. On the left side of the frontal hull armor plate, either a ball-mounted DT machine gun or a flamethrower were to be mounted. There were 60 drums for the machine gun (47×60 rounds) and an additional 15 shots for the flamethrower. The crew was equipped with an unspecified amount of PPSh 7.62 submachine guns.
As the tank was intended to sustain fire from the German 88 mm anti-aircraft guns, the thickest armor was in the front hull plate and front turret, at 120 mm, with other frontal armor portions being 115 mm thick. The rest of the turret was 115 mm, while the rest of the hull was 90 to 100 mm.
The KV-3 proved to be an ambitious plan to quickly create a well-armored and well-armed tank based on previous designs. While work began smoothly, several delays from the Izhora plant and the start of the war greatly delayed the project to the point of cancellation. The complexity of the stamped turret construction, which required new tooling, as well as the unrefined engine sent the project into a spiraling series of delays. However, on paper, the tank would have been an impressive feat, though likely even more plagued by reliability issues than the KV-1.
KV-3 (Object 223) Specifications
7.85 x 3.42 x 2.95 m
Total weight, battle-ready
6 (Commander, gunner, driver, radio operator/bow gunner, 2x loaders)
V-5SN 12-cylinder diesel, outputting 850 hp w/ AM-38 supercharger
In summer 1940, one of the ways through which Soviet officials wanted to improve the firepower of their heavy tanks was to mount an 107 mm gun in the KV-2. This idea was later dropped in favor of new, heavier tanks which were to directly mount the new 107 mm ZiS-6 gun. However, due to the slow progress of development, the KV-2 was brought back, and was used as a gun testbed for firing trials. Due to the start of the war, neither the ZiS-6 nor the heavy KV tanks designed to use it entered service.
Even before the KV-1 and KV-2 entered serial production, Soviet officials sought to improve their raw characteristics. One direction was to add even more armor, like on the T-150. Another was the improvement of the main armament. A document from June 1940 discussed the future of Soviet heavy tank developments. The second point mentioned the mounting of a high-power 107 mm gun in the KV-2. The gun was to have a muzzle velocity of 730-750 m/s and penetrate 100-110 mm of armor at 1,000 m. High rate of fire, high ammunition capacity, as well as both AP and HE shells were desired.
At the time, the KV-1 was still being produced with the underwhelming stopgap 76 mm L-11 gun, while the KV-2 was fitted with the 152 mm M-10T, which left much to desire in most areas. A 107 mm gun with such high velocity would have been formidable against any armored target at the time. It is perhaps this state of “overkill” which delayed the materialization of this project. Furthermore, the situation of the Soviet tank industry was not optimal. The creators of the KV tanks, the SKB-2 design bureau at LKZ (Leningrad Kirov Plant) were stressed with bug fixes for the KV-1 and were already tasked with the development of the T-150 and T-220 heavy tanks. Likewise, the creators of tank armaments, Plant No.92, were just beginning work on the much needed new tank guns, the 76 mm F-27 and 85 mm F-30.
New High-Power Gun
Plant No.172 had the 107 mm M-60 divisional anti-tank gun under development since late 1938, entering service in October 1940 under the designation M1940. However it was deemed too heavy to be mounted in a tank, thus a new gun was needed. It was likely this gun that was originally (in June 1940) meant to be mounted on KV-2. Based on V.G. Grabin’s memoirs (head of Plant No.92 design bureau), a KV-2 had been fitted with an 385 tonne/meter, 107 mm gun, likely an ancient M1910/1930 gun, to test the viability of mounting such a large gun.
A first mention of the 107 mm F-42 appeared on 16 December 1940, when Plant No.92 was already in the process of producing the first prototype. Curiously, they had requested a KV-1 tank to test fit the gun, and due to delays, allegedly fitted the 107 mm gun prototype into the T-28 medium tank instead. No testing was carried out due to lack of ammunition.
Here, it is worth mentioning the differences between the F-42 and M-60 anti-tank guns. The F-42 had a higher muzzle velocity of 800 m/s compared to the 730 m/s on the M-60. The barrel was also longer on the new gun, 5185 mm compared to 4605 mm on the M-60. The breech had also been altered. The M-60 used a clumsy door breech lock, while the F-42 used a vertical sliding breech lock. The shells of the F-42 weighed 18.8 kg.
Later documents reveal that this new 107 mm gun was originally to be designed at LKZ, with a deadline of November 1940, but the plant refused to do so. Only in January 1941 did the SKB-4, the artillery design bureau of LKZ, start work on their own 107 mm gun, the 412-2V, but it was canceled shortly thereafter due to the progres of the F-42.
Aside from the KV-2, in June 1940, the KV-220 was also proposed to be armed with an 107 mm gun. This idea came from the initiative of Grabin and J.Y. Kotin, head of the SKB-2 design bureau, despite the fact that the GABTU specifically requested the main armament of the KV-220 to be the F-30. By August, SKB-2 engineer G.N. Moskvin began working on this hypothetical weapon swap. He concluded that an 107 mm gun would have been too large to fit in the turret of the KV-220, especially considering how long the shells were, at 120 cm, making loading nearly impossible.
By December, it was clear that this gun was supposed to be the F-42, and Grabin still believed that his 107 mm gun would fit in the KV-220. To prove this, he traveled to Leningrad to convince Kotin. He then climbed into the turret (allegedly struggling to fit through the hatch) and attempted, and failed, to lift the 18.8 kg shell from the hull floor into the turret.
The story of the F-42 fitted in the KV-220 did not end here. On 19 February 1941, Marshall Kulik, who was overseeing progress at LKZ, submitted a report where he mentioned that the KV-220s second prototype was to be armed with the F-42 at Plant No.92, where the tank’s turret was waiting. Even more bizarre was that Kulik also mentioned that an F-42 gun was to be mounted on the KV-1 by May, but LKZ, understandably, outright refused to do so.
Tanks vs Guns
On 11 March 1941, the F-42, by this point renamed ZiS-6, re-entered the picture. Soviet intelligence services sent a report to the GABTU and Soviet leadership regarding the development of German tanks. In the section on heavy tanks, several projects were described, but perhaps the most alarming was that of a 90-tonne tank armed with a 105 mm gun.
This was not taken lightly, as neither the KV-1 nor the KV-220 in development were able to deal with such threats. Thus, SKB-2 was tasked by the GABTU with the design and development of a new heavy tank, specifically armed with the ZiS-6 gun, and weighing 72 tonnes. It was named KV-4 (Object 224).
A segment from Grabin’s memoirs showcases perfectly the situation of development at the time. On 4 April, Grabin was having a phone call with Stalin:
Stalin – “Hello, Comrade Grabin,- I want to consult with you. It is believed that a heavy tank which is armed with a low-power gun cannot meet the tasks of a heavy tank. Currently, the issue of re-equipping it is being considered: instead of the 76-mm gun, it is proposed to put a powerful 107 mm. I would like to know your point of view on this issue. It may be difficult for you to evaluate this proposal, since the heavy tank is armed with your 76-mm cannon.”
Grabin – “When our design bureau was issued tactical and technical requirements for a 76-mm gun for a heavy tank, we carefully studied the issues related to tanks and their weapons, and came to the conclusion that the 76-mm gun for a heavy tank is unpromising and does not even meet the requirements of today. We believed that a heavy tank should be armed with a more powerful gun, the projectile of which would penetrate the armor of its tank from a distance of 1000 m. The 76-mm cannon ordered to us was created and installed in the KV-1 tank.”
Stalin – “So, you’ve long had an opinion about the insufficient power of the 76 mm gun on heavy tanks?”
Grabin – “Yes, Comrade Stalin.”
Stalin – “It’s a pity that I didn’t know about it before. So, right now, our estimates do not contradict. Tell me, please, is it possible to put a powerful 107 mm gun in a heavy tank?”
Grabin – “Yes, Comrade Stalin.”
Stalin – “Are you sure that a powerful 107-mm gun can be put in a heavy tank?”
Grabin – “I am quite sure that a 107-mm powerful gun can be put in a heavy tank. But we consider the KV-2 tank unacceptable in terms of the design of the turret. The dimensions of the turret are large, and the shape of the turret is not optimal. Such dimensions for the 107-mm gun were not required.”
Stalin – “So you claim that a powerful 107-mm gun can be installed in a heavy tank?”
Grabin – “Yes, I am deeply convinced that a powerful 107-mm gun can be put in a heavy tank. If I understand you correctly, this gun should be higher in power than the 107 mm modernized?
Stalin – “You understood me correctly. The fact that you already have experience in installing a 107 mm cannon in a heavy tank is great. So, we will install a powerful 107-mm gun in a heavy tank?”
Grabin – “Yes, Comrade Stalin.”
Stalin – “This is very important, Comrade Grabin. As long as we do not arm a heavy tank with such a gun, we cannot be calm. The task must be solved as quickly as possible. This is required by the international situation. Tell me, could you be in Moscow tomorrow? We really need you here.
The following day, Grabin found himself at the meeting with the Secretary of the Central Committee of the All-Union Communist Party A.A. Zhdanov. Also present were the head of the GABTU ,Lt. Gen. Y.N. Fedorenko, as well as LKZ representatives J.Y. Kotin and I.M. Zaltsman, as well as V.G. Grabin and others.
Zhdanov opened the meeting with a bold message:
“The party and the government attach great importance to the rearmament of a heavy tank, I ask you to approach with all seriousness the development of tactical and technical requirements and to determine the timing of the creation of a tank and gun. Deadlines should be minimal. Fascist Germany is walking around in the West. It is possible that in the near future it will attack us. We learned that the Germans are working on the creation of thick-armored tanks with powerful weapons. Our heavy tanks are poorly armed. […] “The draft decision needs to be prepared as soon as possible, therefore, you will have to work late, without leaving the Central Committee. You will eat here, we will provide it. A room is set aside for your work. I am at your disposal at any time…”
Things started off poorly. The LKZ engineers refused to mount a 107 mm gun on their tank. Most likely, this tank was the KV-220 and/or Object 222. This situation brought up a long-time argument between Kotin and Grabin, whether it was the mounting of the 107 mm gun in the KV-220, KV-1, or the mockup T-28 Grabin received instead of an actual tank for the testing of his F-39 gun. The situation was aggravated when Grabin, rather famously, said that the tank is just a chassis for the gun. Naturally, the tank designers did not take this lightly. After Zhdanov calmed down the 5 culprits, work commenced, but not smoothly. Grabin suggested that the new gun had to have 550 tonnes/meter, and with a longer barrel than the M-60. The tank designers objected, fearring that a too long gun would scrape up mud and lead to barrel damage.
The second day, most of the intricacies had been solved, with the exception of when everything should be ready. Once again, Zhdanov intervened:
Zhdanov – “When will the tank be ready?”
Kotin – “As soon as Grabin gives the gun, the tank will be ready,”
Zhdanov – “Comrade Grabin, when will you be able to give the gun?”
Grabin – “In forty-five days,”
Here Grabin recalled that everyone burst into tears, and that he was the only serious one in the room.
Zhdanov – “Comrade Grabin, we have gathered here to seriously resolve the issue, and you are joking.”
Grabin – “No, I’m not kidding, the term I mentioned is justified and quite serious.”
Zhdanov – “You continue to joke, go and think again.”
Grabin also highlights that this topic of 45 days was the subject of many jokes that he would hear often. With further consultation, the tank designers suggested that the number of days should be doubled, if not tripled. When it became clear that progress was not made, Zhdanov stepped in, again.
Zhdanov – “Well, Comrade Grabin, did you think through the deadline?”
Grabin – “Yes.”
Zhdanov – “Probably not forty-five days?”
Grabin – “Forty-five days, Comrade Zhdanov.”
Zhdanov – “And yet you are not serious. I think that the term should be significantly increased.”
Grabin – “Comrade Zhdanov, why does a short term cause homeric laughter and is considered frivolous, while a long term finds support and approval?”
Zhdanov – “We do not know of a single case where a new tank gun was created not only in forty-five, but even in ninety days. We believe that this will be a great opportunity for us to work together with our partners.”
Grabin – “I agree. Previously, it was not the case. Now it is. I ask you, Comrade Zhdanov, to write down in the draft decision: “The deadline for the production of a prototype tank and gun should be set forty-five days from the date of signing the decision.”
This was the deadline set in the contract. Grabin was set to leave back to Gorky even before the contract was fully signed. Before leaving, Zhdanov said that if Grabin was not able to meet the deadline, to just call him and tell Stalin and they would extend the contract. Grabin thanked him.
Naturally, much of the above should be taken with several grains of salt, as these clearly-one sided memoires were written many years after the fact. Nonetheless, they still provide valuable information on how Grabin viewed the ordeal.
On 7 April, the contract was signed, and further heavy tanks were ordered. The KV-3 (Object 223) and KV-5 (Object 225) were also meant to fit the same 107 mm gun. The KV-3 used an up-armored hull of the KV-220 and an enlarged turret, specifically made to fit the ZiS-6. The KV-5 was even larger than the KV-4, weighing 90 tonnes and with 170 mm of frontal armor.
The Gun is Ready, the Tanks are Not
Now that there were several vehicles in the works to mount the ZiS-6, work on it progressed. On the same day as signing the contract, 7 April, over at Plant No.92, a development program for the ZiS-6 was drawn up. Firing trials were to be undertaken on 15 May. Between April and May, ammunition production was set, and ballistic trials were laid out. However, several changes had to be made to the gun for use on tanks. Firstly, the shells were to be single piece, as opposed to 2-part. A gun rammer and bore evacuator were to be added to the gun for use on these tanks. On 14 May, the ZiS-6 was finished. Grabin was now able to boast that he made his gun one week faster, in just 38 days.
Naturally, work on the ZiS-6 was far more advanced compared to the heavy KV tanks and the gun had to be tested. The only vehicle readily available and able to mount the ZiS-6 was the KV-2. Thus, on 17 April, Fedorenko sent a letter to Zhdanov ordering that said gun was to be mounted on the KV-2 for trials. On 27 May, Plant No.92 shipped a ZiS-6 gun with serial number 2 (other sources claim 1) to LKZ for mounting on the KV-2, and arrived on 1 June. It was issued that the Izhora plant was to manufacture the gun mantlet and gun mount of the KV-3 and be mounted on a KV-2. Yet the Izhora plant was moving slowly, causing Marshall Kulik to intervene on 18 June, ordering the Izhora plant to deliver required parts and that testing shall commence with the ZiS-6 in a KV-2 with serial number B-9680.
While the KV-4 and KV-5 were long-term projects, the KV-3 was to act as a stopgap. On a contract signed 1 June, KV-3 was to enter production in August 1941, with 500 units to be built until the end of the year. Thus, Plant No.92 also had to deliver 500 guns before the end of the year. Grabin claimed that he began production of the guns far before it was ordered by the military. By the time the order of production was given, they had “dozens” of guns ready.
Design & KV-2
The KV-2 was born from the urgent need for a bunker buster to fight through the Finnish fortifications on the Karelian isthmus during the Soviet-Finnish war. However, due to the immediate need, a specially designed vehicle could not be finished in time. Thus, as a quick measure, an enlarged turret armed with an 152 mm M-10T gun was mounted on a prototype hull of the KV tank. The assault tank would prove slow and overweight, while the gun, despite its large size, had underwhelming performance against static defenses. The first 24 vehicles used a tall, complex turret, while later production models featured a more compact and efficient turret. In total, 204 such vehicles were built, but most were lost in the first stages of the fight against the Axis, most breaking down or being captured.
The crew was the same as usual, comprising six men; commander, gunner, loader, and the loader assistant in the turret, and the driver and radio operator in the hull. As the hull was identical to that of the KV-1, it was powered by an 500 hp V-2K diesel engine, for a top speed between 30-35 km/h. It had two fuel tanks for a total of 600 liters.
As the tank was used as a testbed, much of the KV-2 tank remained untouched, with the main difference being that the gun mantlet had been changed to that of the KV-3 to accommodate the new gun. Due to the accelerated nature of the work, several details had not been worked out or converted. Firstly, the ammunition stowage racks had not been changed, so rate of fire was particularly low.
The tank arrived at the Gorokhovets proving grounds on 25 June, and the trials began. The ammunition used had additional explosive charges, increasing the muzzle velocity to 840 m/s. In total, 618 shots were fired, but the increased charges caused several issues. After 315 shots, the gun rammer broke. After 486 shots, the accuracy decreased considerably. The commission blamed these issues on barrel wear caused partly by the increased muzzle velocity of the shells. On the other hand, penetration was excellent. It penetrated 120 mm armor plates thick armor plates angled at 30° from 1,600 meters.
The damaged gun was transported back to Gorky, where it was repaired. By 10 July, Plant No.92 had already completed four additional guns, as well as having 214 guns in various stages of production.
There was still no sign of any tanks for Grabin’s gun. The truth was that work on the KV-4 had completely stalled after May. Regarding the KV-3 and KV-5, work was continuing timidly. The KV-3 had a full scale mockup and most blueprints ready, while the KV-5 was still just entering the blueprint stage. Given the circumstances, the GABTU altered their request, asking for just 35 ZiS-6 guns, 5 in October, 10 in November and 20 in December.
The start of the war on 22 June significantly affected these projects, with LKZ having to ramp up KV-1 production, as well as focusing on repairs of tanks. The situation aggravated when German forces were approaching Leningrad in August, and thus the SKB-2 design bureau was evacuated to the ChTZ, in Chelyabinsk. While the KV-4 and KV-5 were outright canceled, plans of continued work on the KV-3 lingered. Eventually, by the end of 1941, it was obvious that nothing would come out of it either.
Realizing his mistake of prematurely starting production of the gun, in July, Grabin pitched the idea of fitting it on the KV-2 directly, but this went nowhere, as KV-2 production had already ended the previous month. In September, he proposed the ZiS-6A, a system similar to, if not directly for, the KV-4, with a coaxial 45 mm 20-K gun. This went nowhere as well.
Despite Grabin’s victory in his personal vendetta with the tank designers, his disappointment over the situation was considerable:
The story of the ZiS-6 does not end here. It was used to develop some even larger 107 mm guns, like the ZiS-24, but this gun also suffered a similar fate in spring 1942. More importantly however, the ZiS-6 was remembered in February 1943, when the Tiger appeared. Stalin called Grabin once again, who assured that he could produce the ZiS-6 in 15-20 days. However, nothing materialized.
The fate of KV-2 with serial number B-9680 is unknown, as it was last mentioned as being in Plant No.92s stock in September 1941.
The KV-2 107 mm testbed proved that there were several issues with the ZiS-6 gun, and Grabin’s confidence to start production prematurely would be a mistake. The gun still needed refinements, and eventually, the heavy KV tanks which were meant to mountmount it were canceled with the outbreak of the war.
KV-2 with 107 mm ZiS-6 testbed Specifications
6.95 (hull) x 3.32 x 3.25 (m)
Total weight, battle-ready
6; commander, gunner, 2 loaders, driver, radio operator
Even before the KV-1 entered mass production, there were plans to improve its characteristics, most importantly the armament and armor. One of these was the KV-220, an attempt to improve the armor of the KV-1 up to 100 mm, and increase firepower with an 85 mm F-30 gun. Designed and built at the Kirov Leningrad Plant, two prototypes were finished in late 1940 and mid-1941 after a convoluted history. They then saw combat in the Leningrad area with the start of the Great Patriotic War (Operation Barbarossa).
The experiences gathered during the Winter War (November 1939 – March 1940) against Finland gave the Soviets invaluable tactical and technical information regarding development and use of heavy tanks. The massive SMK (from LKZ, Leningrad Kirov Factory) and T-100 (from Plant No.185) multi-turreted tanks were attempts to create a successful breakthrough heavy tank. Nevertheless, their fundamentally troubled design, based on the hopelessly obsolete T-35, would fail them. The U-0, essentially a smaller, lighter, one-turreted SMK, would prove to be far more successful during its trial combat period on the Karelian Isthmus. Consequently, on 19 December 1939, 50 such tanks were ordered. The tanks would be known with the acronym KV, from Kliment Voroshilov, the People’s Commissar of Defense of the Soviet Union at the time, but as they were preseries production, each vehicle was documented with U-XX, with each new tank receiving a new, higher number.
Despite the KV’s improvement over its larger predecessors, it was still far from perfect. By July, only 32 tanks had been built (including 14 KV-2s, or, as known at the time, ‘Big Turret KVs’). This was caused by the fact that the KV’s were not fully refined yet, with countless mechanical and production flaws. Each new U-series tank was unique, with different features meant to fix previous problems. This was accounted for from the beginning, as mass production was expected to begin by 1941. However, Stalin’s patience waned. In what would become “The Stalin Task” via a decree from the Council of People’s Commissars of the Soviet Union, it was required that LKZ reach a yearly production quota of 230 KV tanks of both turret variants (130 small turret and 100 big turret), essentially forcing the still unrefined tanks into service. This move would have detrimental effects on the KV-1 and KV-2 throughout their service life.
Only by August 1940 could full scale production of the KV tanks begin, with 20 built in August and 32 units in September, surpassing the expected monthly quota of 20 vehicles.
As early as May 1940, the GABTU (Main Directorate of Armored Forces) and the People’s Commissariat of Heavy Engineering considered improving the armor of the KV-1. This was a curious move, as the KV-1, with 75 mm of armor all-around, was capable of withstanding fire from most anti-tank guns used at the time. Perhaps even more bizarrely, would be that the KV-1 was struggling to function at its 44 tonnes. The wiggling room for additional armor was small.
First concrete mentions of thickening the armor of the KV came on 11 June, suggesting to up-armor the tank to 90 to 100 mm. Around a month later, on 17 July, the Council of People’s Commissars of the Soviet Union adopted decree No. 1288-495§, which stated:
By November 1, 1940, the Kirov Plant will produce two KV tanks with 90 mm of armor: one with a 76 mm F-32 gun, the other with an 85 mm gun. The Izhora Plant will deliver one hull at the end of October, the production of the tank is scheduled to be completed by November 5. The second hull will be made by November 5th.
By December 1, 1940, the Kirov Plant will produce two KV tanks with 100 m of armor: one with a 76 mm F-32 gun, the other with a 85 mm gun. One hull will be delivered by the end of October and by the end in November.
The first paragraph discusses two tanks, both integrating 90 mm of armor all-around. The variant armed with the 76 mm F-32 gun would become the T-150, while the one with the 85 mm F-30 would become the T-221.
The second paragraph mentions another two tanks, with 100 mm of armor all-around. Like previously, one was to be armed with the 76 mm F-32 and the other with the 85 mm F-30. The latter would become the T-220. What exactly happened to the variant with the 76 mm gun is unclear. It was likely either dropped in favor of the T-150 or incorporated within the T-220.
Despite the decree, work did not begin immediately. LKZ was working full-time on improving the existing KV-1 and KV-2, and preparing for their mass production. Further delays were caused by the GABTU sending the specific technical requirements late.
The new tanks were to be designed at LKZ’s SKB-2 design bureau and the prototypes would be built at the Izhora plant. The projects were handled by the head of SKB-2, J.Y. Kotin, who, in August 1940, would appoint several teams for the development of the tanks. For the T-150, Kotin appointed Military Engineer L.N. Pereverzev as head of the project, while the T-220 team was to be headed by L.E. Sychev. An experienced tank engineer, Sychev had worked on the T-28, SMK, and KV-1, having completed his bachelors at SKB-2 in 1932 and after graduating in 1934, starting work at SKB-2. At some point during the project, Sychev was replaced by B.P. Pavlov as head designer. Gun installation and mechanism were designed by P.F. Muraviev, while the transmission was designed by N.F. Shashmurin. Ultimately, the design team of the T-150 (and likely KV-220 as well) consisted of B.P. Pavlov, L.E. Sychev, V.K. Sinezersky, S.V. Kasavin, F.A. Marishkin, and N.F. Shashmurin.
When designing the T-220, Sychev’s team encountered several issues. It was clear that the hull of the KV-1 was not big enough to accommodate the larger turret or additional 25 mm of armor. Additionally, the tank would have been significantly heavier, and a much more powerful engine was required. The clear choice was to lengthen the hull by 1 roadwheel, allowing for a much larger 850 hp V-2SN engine, as well as comfortably fitting a longer turret. Ground pressure was also lowered. The tank was named T-220 and later called Object 220 and KV-220.
Fitting the 85 mm F-30 gun in the KV-1 turret was ruled out, as it was simply too large. Instead, a turret inspired from the earlier designed KV-2 was drawn. It featured long side walls, allowing the crew members to adequately operate the gun, as well as a smaller turret on top armed with a DT 7.62 mm machine gun.
By September, the technical documents and drawings were ready and were sent to the Izhora plant for prototype production. However, the Izhora plant Hall No.2 was working at full capacity with the production of KV-1 and KV-2 tanks, with four tanks on the lines at the same time. Consequently, the construction of the prototype was delayed, and the tank was sent to the factory, complete, on 7 December, six days late. This first tank was given serial number M-220-1.
A second KV-220 was to be built as well, with the serial number M-220-2. The exact characteristics of this prototype had been tinkered with several times, which led to a very delayed production, with various sources claiming that this was in fact the Object 221, while other data contradict this claim. It is possible that this prototype was to be the 76 mm F-32 armed KV-220, but at the start of February, the turret of the tank was at Plant No.75, awaiting installment of the same 85 mm F-30 gun as on the M-220-1. On 19 February, the tank was instead to be armed with the 107 mm ZiS-6 after a series of studies had been made. Construction of the second prototype would only begin by 7 June and the military representative of LKZ, Military Engineer 2nd Rank A. Shpitanov, would claim that the tank would be ready no earlier than 10-15 July.
Between the T-150 and T-220, there was a third vehicle, as originally requested in July 1940. It was to have 90 mm of armor, as the T-150, but with the same 85 mm F-30 gun as on the KV-220. The result was essentially just a KV-220, but with just 90 mm of armor, as opposed to 100 mm, and named T-221 (Object 221). Thus, due to its appearance, this vehicle is often confused with the KV-220. On 19 February, its armament was changed to the 76 mm ZiS-5 gun, and the turret was to be produced by 1 March. Only a mock-up was built in March 1941, and its mock-up chassis was later used on the mock-up of the Object 223 (KV-3).
Object 212 SPG
Another project based on the KV-220 was the Object 212 SPG, also named in documents as just 212, but not to be confused with the KV-based tractor with the same index. It was meant as a genuine bunker buster vehicle, intended to replace the KV-2, as a result of the sour taste left by Finnish fortifications encountered during the Winter War. It was to be armed with the 152 mm Br-2, based on the inverted chassis of the KV-220, with a large casemate. Only some components were built until the evacuation of SKB-2 in August 1941, and the entire project was transferred to UZTM factory, where development would continue slowly until the project died out, largely due to the cancellation of the KV-220 and later the KV-3.
The addition of 25 mm of armor all around and the larger 85 mm gun necessitated a major overhaul of both the hull and turret of the KV-1. The thickening of the armor was done outwards, which allowed for very similar interior dimensions to those on the KV-1.
Firstly, the hull was elongated to over 7.8 m, most noticeable with the addition of an extra roadwheel and return roller. The lengthened hull allowed for the mounting of a larger engine, as well as decreasing the ground pressure of the tank. As the tank was to be far heavier, a new engine was required, and the 850 hp V-2SM experimental engine from Plant No.75 was chosen.
Secondly, and most importantly, the turret was a completely new design. It was largely based on the turrets of the KV-2 and Object 222. A large curved mantlet with gun housing was mounted on the flat frontal turret face. The sides were vertically flat, but had a slight curve along their length. The rear was also flat, but featured a large square door, used for entry and exit of the crew, ammunition replenishment, and removing the armament. The sides of the turret were flat, as opposed to angled at 15°, as both Kotin and factory director I.M. Zaltsman noted that mounting the turret walls at a right angle allowed for far stronger joints and easier production, without sacrificing much in terms of protection.
Across the upper edge of the turret, five handles were added for easier climbing on the large turret for the crew. On each side, a firing port for crew weapons was added.
Perhaps one of the most interesting features of the KV-220 was the small secondary turret, which also acted as a commander’s cupola, with full 360º traverse. It was very similar to those designed by Plant No.185 for their T-103, though there might be an element of coincidence. It had four periscopes, one facing each direction. A 7.62 mm DT machine gun was mounted within. The cupola armor was also 100 mm thick all around, making it cramped when loading and firing the machine gun. The cupola was just large enough for the commander to fit his head. No service hatches were given. Another problem with the cupola was the firing blindspots created by the periscopes in front of it, especially the rotating PTC periscopes.
The larger turret and gun now required an additional loader, bringing the total crew to 6: tank commander, gunner, two loaders, bow machine gunner/radio operator, and driver-mechanic. The latter two were seated in the hull front, much like on the standard KV, with the driver in the center and radio operator to his left. Behind the driver was an emergency exit hatch in the floor.
The other four crew members were cramped in the turret, with the gunner to the left of the main gun. The commander was placed behind him and could control the machine gun turret. The two loaders were to the right of the gun.
The hull armor was nearly identical in layout and angling to the one on the KV-1, just 25 mm thicker, reaching 100 mm. The front had an angled lower plate, 100 mm, thick meeting with the belly (30 mm) and upper frontal plate (90 mm at 20º from horizontal) meeting into the frontal shield (100 mm at 60º). The sides were completely flat, also 100 mm thick. The rear, just like on the KV-1, consisted of two plates, the lower being 100 mm and the upper portion just 50 mm, as the engine cooling system was behind it.
The turret had 100 mm of armor all around, and the joints were welded together and reinforced by rods, which would run across from one plate into the other. It is important to acknowledge that the KV-220 was one of the first tanks where the Soviet industry had to deal with such thick armor.
The engine used was the V-2SN 850 hp diesel engine developed by Plant No.75, which was a boosted variant of the V-5 engine (with a supercharger from the AM-38 aircraft motor combined with a pressurization system), which itself was a boosted variant of the V-2K engine used on the KV-1. Naturally, the engine was bound to become problematic due to its unstable nature. The tank was able to carry 825-845 liters of fuel.
Unlike its smaller ‘brother’, the T-150, the unreliable KV-1 gearbox was not used on the KV-220, but rather a reinforced and slightly modified version designed by N.F. Shashmurin. These alterations included a more compact box, improved tolerances and better dynamics. This was a crucial step in the right direction, not just for the KV-220 but for future KV tanks, which were to be fitted with better gearboxes.
The main armament on the KV-220 was the 85 mm F-30, developed at Factory No.92 by V.G. Grabin. It was based on the F-27 75 mm gun, but chambered for the larger 85 mm round and with improved recoil systems. The gun was installed and tested on the T-28 in spring 1939, and after a series of firing trials, was deemed satisfactory. Ballistically, the gun was near identical to the 52-K anti-aircraft gun, and shared ammunition.
Mounting of the gun on the KV-220 was conceived by P.F. Muraviev. A PT-6 sight would be used for aiming, and a PTK panoramic periscope for battlefield vision for the gunner. The tank carried 91 rounds for the 85 mm gun, with at least 15 rounds stored in the turret bustle. The rest were in the hull, stowed in two different frames.
Secondary armament consisted of three DT 7.62 machine guns, one in a ball mount in the hull bow, one coaxially (right) with the main gun and one in the cupola. For these, 64 drums were provided, for a total of 4,032 rounds.
85 mm F-30 gun specifications
Muzzle velocity (m/s)
Shell weight (kg)
88 mm from 1 km @ 30º
After the KV-220’s (M-220-1) reception in early December, the tank was inspected and prepared for trials. On 14 January 1941, an order from the People’s Commissariat of Defence and People’s Commissariats of Heavy Engineering requested that the T-150 and KV-220 tanks undertake driving and chassis trials at LKZ.
A commission, headed by assistant head of testing, Military Engineer 1st Rank Glukhov, and consisting of GABTU and LKZ officials, were to analyze the tanks and establish the following goals:
Determining the tactical and technical characteristics of the tank
Identifying the shortcomings in the designs and their elimination prior to mass production
Judging whether it is possible to conduct military tests
Accumulating data for operating and repairing the tanks
From a letter dated 28 January 1941 from Glukhov, reporting on the progress of the trials, several alarming details can be found, as both tanks broke down during driving trials. For the KV-220, it broke down while driving around the factory, on 21 January, as the engine failed after its main bearings melted. A new engine would be fitted a week later.
Another issue found with both the T-150 and KV-220 was when they were weighed. Both had surpassed the initial weight threshold imposed. The KV-220 weighed 62.7 tonnes, instead of 56 tonnes.
A second report from Glukhov would reveal the true failure of the KV-220’s engine. The tank had traveled 106 km and the engine worked for 5 hours and 51 minutes, allowing the 62.7 tonne tank to reach a top road speed of 21.2 km/h (according to Yuri Pasholok, 33 km/h) and averaged 18.6 km/h. During operation, hot engine oil was squirted from the engine cooling vents on top, as well as encountering power loss due to piston ring wear. Thus, oil usage spiked uncontrollably, to 15.5 liters per hour of operation, or 0.83 liters per km.
Unlike the T-150, the KV-220 never undertook firing trials either, mostly because of the unbalanced gun and the foot trigger being poorly made, an issue discovered in December 1940, and which would be postponed. On 19 February 1941, after a letter specifying the issue from Deputy People’s Commissar of Armament Mirzakhanov, Marshall Kulik would request that the KV-220’s turret be sent to Plant No.92 for alterations of the gun mechanism, but a specific date or deadline was not given.
The failure of the engines was not a surprise. In fact, before the trials, Plant No.75, through T.P. Chupakhin, could not guarantee the operation of either the V-5 engine on the T-150 or V-2SN on the KV-220. On 28 January 1941, another V-2SN engine was brought in and trials continued, but this one failed a few days later, on 3 February. Another engine could not be provided until 15 February.
In order to fix these crucial problems, a commission was set up on fixing and refining the V-5 and V-2SN engines, consisting of Glukhov, Chuptakhin, head of tank production at LKZ A.I. Lantsberg, as well as representatives from GABTU. The commission would determine that the engine trials were done prematurely and that they required operation testing, not field trials on tanks. Plant No.75 was tasked with finishing testing and fine tuning the engines by 10 April, and by the same date, the engines and improved cooling systems were mounted and tested on said tanks.
When the news of the failed trials of both tanks reached the GABTU and People’s Commissariat of Heavy Engineering, the head of the armored department of the GABTU, Military Engineer 1st Rank Korobkov, sent a letter to LKZ director I.M. Zaltsman demanding the engines to be fixed and continuing trials.
The KV-220 was not a cheap tank project. A report dated 30 May 1941 mentions in detail the developmental costs of KV experimental tanks, which in total amounted to 5.35 million rubles. The KV-220 alone cost 4 million rubles, this sum including both the KV-220-1 and KV-220-2. For context, a KV-1 Mod.1941 would cost between 523,000 to 635,000 rubles.
Stage of KV-220 Development
Price (thousands of rubles)
Prototype construction and factory trials
Proving ground trials
Drawing correction after trials
Repair of prototypes and improvements
Source: CAMD RF 38-11355-101
Fitting the 107 mm F-42 (ZiS-6)
Both Kotin and Grabin had juggled with the idea of installing an 107 mm gun in a tank since 11 June 1940, originally in the KV-2. By August 1940, SKB-2 engineer G.N. Moskvin was tasked with researching the fitting of a 107 mm gun inside the KV-220 turret. The gun would turn out to be the 107 mm F-42, developed by December of the same year, and which was later indexed ZiS-6.
Initial calculations revealed that fitting the F-42 gun in the KV-220 turret would have raised great challenges, especially regarding the movement of the shells within the tank, as they were simply too long. Factor in bouncing of the tank while driving, and the loader’s job was impossible. The round was 1,200 mm long and weighed 18.8 kg. Splitting it into two, like on larger 122 mm and 152 mm rounds, was impossible.
Chief designer of Plant No.92, V.G. Grabin, on a trip at LKZ, would try to convince Kotin and the tank engineers that it was possible to fit the F-42 inside the KV-220. After struggling to fit inside the turret hatch, he was unable to lift the shell from the hull floor and into the turret. He would then criticize the tank designers for their reluctance to change the design and stated that the tank was merely a gun platform.
The second KV-220 prototype, M-220-2, was to be originally armed with the 76 mm F-32, and later the 85 mm F-30, as on the first prototype. However, by 19 February, the F-42 would appear again in a letter from Marshal Kulik, stating that the second prototype of the KV-220 was to be armed with the 107 mm F-42 gun at Plant No.92, where the turret was already at. Although the KV-220 was never fitted with the gun, its immediate offspring was.
By March, the improved engines from Plant No.75 were ready to be tested, but the situation was starting to change. On 1 March, the T-150 had been replaced by the Object 222, which featured a new, improved turret on the same hull. Shortly after, on 11 March, a letter from the intelligence services to the GABTU regarding German tank developments would lead to a series of changes in tank developments.
The highlight of the report was a 90-tonne Pz.Kpfw.VIII armed with a 105 mm gun, which would become the Löwe in late 1941. As a response, on 17 March, the GABTU tasked LKZ with designing an equivalent tank, namely the Object 224 or KV-4, weighing 72 tonnes and armed with the 107 mm ZiS-6, a secondary 45 mm gun, various machine guns, and a flamethrower. Frontal armor was to be 130 mm and side armor 120 mm.
By 7 April, the GABTU had reconfigured their requests. The Object 223 was born, which was a direct evolution from the KV-220 with thicker armor, up to 120 mm on the hull, and an entirely new turret made out of stamped armor sheets, also fitted with the ZiS-6. The turret was far larger than that of the KV-220, made out of 120 mm armor. The KV-4 was also altered, with a weight of at least 75 tonnes and side armor thickness increased to 125 mm. Lastly, a 100-tonne tank was requested as well, Object 225 or KV-5, with 170 mm of frontal armor, 150 mm of side armor, and the same 107 mm gun.
As a result of these developments, the KV-220 became sidelined, but its mere physical existence made it crucial in the development of the Object 223 (KV-3). For trial purposes, the hull of the KV-220 would be used, but with a V-5 engine which was to be replaced with a V-2SN once they were available. Between 12 and 14 April, weight tests with 70 tonnes were done on the chassis, to simulate the weight of the KV-3, with several issues discovered:
Leak from the V-5 engine’s crankcase
Incredibly slow speed and low power, the tank only being able to drive in 1st and 2nd gear off-road
2 idlers had to be replaced
2 roadwheels were damaged
1 torsion bar was damaged
With this smaller engine, the trial tank sustained a consumption of 2.9-3.2 liters per kilometer (31-34 liters per 100 km).
The Object 224 (KV-4), namely the winning design of the KV-4, by N.L. Dukhov would be an enlarged KV-220. The hull was much larger and the turret was equipped with a loading assistant mechanism for the large shells. There are at least two documents mentioning the KV-220 as the KV-4, before the Object 224 existed, which makes sense considering the T-150 was also temporarily called KV-3.
During May and June 1941, SKB-2 was busy working on the technical details of the Object 223, 224, and 225, as well as conducting firing trials of the ZiS-6 gun mounted on a KV-2. But with the Axis’ invasion of the Soviet Union, priorities changed. The heavy tank losses suffered by the Soviets required massive efforts from both repair units, but also factories to ramp up tank production and repair. Thus, progress on the massive heavy tanks slowed down. Likewise, the KV-1 proved to be catastrophically unreliable, although its excellent armor shined several times, and work had to be done to improve the tank.
It is worthy to mention that during the same period, the KV-2 was armed with the 107 mm ZiS-6 fitted via a KV-3 mantlet and firing trials were held.
Despite the development of the new heavy tanks, work on the KV-220 continued. On 31 May, a third V-2SN engine was delivered by Plant No.75. The new engine (serial number 1193-03) worked well, and by 20 June, the tank had rolled a total of 1,979 km, of which 583 km between May and June. The engine worked for 27 hours and 21 minutes. There were still several problems with the tank:
10 of the 14 roadwheels sustained rim damage and one was cracked.
5 return rollers suffered damage to the rubber.
Right final drive failed due to failure of 2 ball bearings, 2 roller bearings, 1 cone bearing, and the main gear was worn out and had heat damage
In response, changes were made to the tank, such as thickening the amount of rubber on the return rollers, of which half had rubber compressed at 16 tonnes and the other half at 18 tonnes. Other changes were the replacement of old filters with the experimental ‘Vortex’ oil filters , which had a mushroom shaped filter for trapping oil, as well as new exhaust manifolds and compensators.
For LKZ, the situation turned sour in August, when the German forces were knocking on the doors of Leningrad. Many SKB-2 engineers were evacuated to the ChTZ plant in Chelyabinsk, alongside some tank prototypes for further work, like the KV-3 (Object 223), which was meant to continue development. The KV-4 and KV-5 were discontinued. Interestingly, based on an order from Zaltsman on 30 June, the KV-3 was to be shipped to ChTZ with the V-2SN engine from the Object 220. This likely never happened.
The T-150 and the two KV-220 prototypes suffered a different fate. Kliment Voroshilov, member of the State Defense Committee, had a meeting with LKZ officials, including I.M. Zaltsman in Smolny, requiring prototype vehicles to be made combat ready in order to defend Leningrad. According to Military Engineer A.F. Shpitanov, 20 tanks were prepared for combat. They were placed in the Kirov district in Leningrad.
But how exactly the KV-220 tanks were to be used in combat was unclear. The M-220-1 prototype was functional, but the 85 mm F-30 was never tested and the gun was unbalanced, thus unsuitable for firing. The M-220-2 prototype had just left the production line in mid-July, but it still had no turret. The logical solution was that each of the tanks were fitted with standard KV-1 turrets, armed with the 76 mm F-32 guns.
The two KV-220 prototypes were sent to the 124th Brigade, with prototypes M-220-1 and M-220-2 being sent on 5 and 16 October respectively to defend Leningrad district. Not much is known about the fate of the first prototype, but the second one has a much more interesting story.
Documents show that the 124th Brigade, including tank M-220-2, named ‘For the Motherland!’, and likely prototype M-220-1 as well, were engaged in combat in the Ust-Tosno area, south-east of Leningrad, alongside 43rd Rifle Division.
On 11 November, at 12:00, the 124th Brigade and 147th Infantry Regiment assaulted a railway bridge in the direction of Ust-Tosno. Fighting commenced around the railway embankment and the bridge over the Tosna River. In total, 19 KV tanks were lost, of which 5 were burned. The KV-220 (serial number M-220-2) was likely one of these.
Russian historian Maxim Kolomiets interviewed with D. Osadchim, who was commander of a KV tank company belonging to the 124th Brigade in autumn 1941. Regarding the KV-220 he recalled:
“In the autumn of 1941, our brigade received several KV tanks for replenishment, one of which was called “For the Motherland!”. It was made in a single copy at the Kirov plant. It had the same capabilities as the KV tank, but had enhanced armor protection, a weight of more than 100 tonnes and a more powerful turbine engine. When driving in higher gears, the engine whistled, and this whistle was very similar to the whistle of the Junkers dive bombers. The first time after receiving the tank, when driving, the brigade even gave the signal “Air!” (raid). The tank entered my company, and at first they wanted to appoint me as its commander, but then my deputy, an experienced tanker, Lieutenant Yakhonin, became its commander. The tank was considered almost invulnerable to enemy artillery and was intended for assaulting fortified positions.
In December 1941 (I do not remember the exact date) our brigade was given the task of breaking through the German defenses in the Ust-Tosno section – the railway bridge, crossing the Tosna River and, in cooperation with units of the 43rd Rifle Division, developing an offensive on the Moscow State River. In the first echelon, I attacked as part of the 2nd Tank Battalion under the command of Major Paikin, while in the 1st Battalion was the tank “For the Motherland” from my company. In this battle, the tank was given the task of capturing the railway bridge over the Tosna River and holding the bridgehead for the approach of the main forces. The battle unfolded in an open area. The frozen top layer of peat bog could not hold the tank. When it came close to the bridge, it was met with fire from German heavy guns, and radio contact with them was lost. I was at the battalion’s command point at the time. When communication with the tank “For the Motherland” was interrupted, I tried to make my way to the scene along the railway embankment. When I managed to crawl up to the tank, I saw that the turret had been knocked down and the entire crew had been killed.”
It is important to highlight that Osdachim’s report was not entirely accurate, though it is understandable, as the interview took place at least 40 years after the fact. Nonetheless, it provides a good picture of how its users saw the machine, as well as the events of how it was lost.
In a tank write-off report from the 55th Army, the tank M-220-2 from 124th Brigade was listed as irreversibly lost via burning and it mentions that the tank had not been recovered. Its crew, tank commander Jr. Lieutenant Yakhnin, driver-mechanic Kypuladze, gunner Efremov, radio operator Matinov, loader Antipov, and radio operator Afanasyev, all succumbed to the fire. After the engagements, 17 KV tanks were recovered.
On 18 March 1942, a KV-220 tank was listed in the inventory of the 84th Heavy Tank Battalion, part of the 55th Army. The tank was also named ‘For the Motherland!’ and was commanded by Lt. Smirnov and crewed by Pugay, Prokhorov, Boykov, and Vikhorov.
In late 1942, one KV-220 was repaired at Plant No.372. A propaganda video titled Leningrad’s Struggle from 1942, shows a KV-220 with a KV-1 turret and painted white being lifted off the repair line of Plant No.372. Here, the tank was fitted with a standard V-2K engine. It is unknown which of the two tanks it was.
Normally, burning of the tank would mean scrapping, but the KV-220 with serial number M-220-2 would reappear once again in a report on 8 February 1943 in the tank inventory of the 12th Tank Training Regiment. The tank, still with the slogan ‘For the Motherland!’ was appointed to tank commander V.V. Strukov. The tank would be used for training until 1944.
The other KV-220, M-220-1, likely had a much shorter fate. In autumn/winter 1941, the tank was sent to defend the northern Kirov district, western Leningrad, with driver-mechanic V.I. Ignatiev. The vehicle was assigned to defend Petergofske Boulevard at the bridge over the Krasnenkaya River (a portion of which today is called Stachek Avenue), about 1 km from LKZ. The tank was likely lost here.
In 1949, before the 10th Anniversary of the start of defense of Leningrad, Kotin proposed the creation of a monument in the exact spot where the KV-220 was lost. The monument was unveiled in 1951 and still stands to this day, and displays a KV-85 tank (actually a hybrid between the KV-122 prototype hull and IS-1 prototype turret) in Leningradsky Square.
It was not just the hulls of the KV-220 that saw combat, but also the turret of the first prototype. After it was dismounted from the tank, it was sent to Karelia, where it was integrated into a static firing bunker (BOT) in the 22nd Karelian Fortified Area. It was indexed BOT KV with 85 mm ‘Victory’ gun. It would not see action. This would not be the only turret to suffer this fate, the T-100Z prototype turret was also moved into a Karelian firing point.
The KV-220, much like its heavier brethren, can be today seen as a large waste of resources, at a time when the Soviets officials and LKZ were rushing the unfinished and unreliable KV-1 into service. The heavier tanks, like the KV-220 and KV-3, although having excellent characteristics on paper, would prove to be expensive, complicated, and their origination from the KV-1’s mechanical components, although improved, would have likely affected the even heavier tanks.
Regarding the KV-220, the Soviets had essentially designed, built, and tested a heavy tank on similar capability levels as the infamous German Tiger I tank. While this comparison might seem of historical irrelevance, it was made by Kotin himself after seeing the Tiger tank for the first time.
The first Tiger I tank was captured by the Soviets on 16 January 1943, the tank having been disabled by artillery fire, and a second almost intact Tiger, with technical documents, tools, and ammunition, was captured on 17 January. A rifle platoon and 4 Soviet tanks were sent in for recovery. Both tanks were sent to the Kubinka proving grounds, where both J.Y. Kotin and head of Plant No.100, A.S. Ermolaev, who also worked at SKB-2 before the war, were able to analyze the tank. It is here where they would learn that the Germans were just now fielding a tank on par to the KV-220, designed over 2 years prior. After the analysis, Kotin would write:
“The tank was impressive, it had an 88 mm cannon and two machine guns. Frontal parts of the hull and turret are protected by strong armor. Despite this data, we saw the tank’s “Achilles heel” so to speak– a vulnerability. Previously, Hitler’s machines were lighter, more maneuverable, developed greater speed – in a word, they were created for the offensive. “Tiger” weighed almost 55 tons, moved slowly, was clumsy, was more suitable for defensive combat. By the way, it was because of its poor maneuverability that it fell into our captivity.”
One can argue Kotin was describing his earlier heavy tank creations, though it is true that the Soviets were not fighting an offensive war.
The KV-220 was a powerful heavy tank based on the KV-1 and was well ahead of its time in terms of technical capabilities. However, much like its predecessor, the KV-1, it was plagued by mechanical problems, primarily in the form of the experimental V-2SN engines. Once the powerplant had been sorted, it proved to be a capable platform, which unfortunately never got to test its equally capable 85 mm F-30 gun. While it did serve as a platform for the even more powerful KV-3 and KV-4 tanks, the entire philosophy of adding extra armor and large armaments on the platform of the KV-1 was faulty. The two KV-220 prototypes would see action on the outskirts of Leningrad, but were lost in combat.
KV-220 (Object 220/T-220) Specifications
7.83 x 3.41 x 3.11 m
Total weight, battle-ready
6 (Commander, gunner, driver, radio operator/bow gunner, 2x loaders)
V-2SN 12-cylinder diesel, outputting 850 hp w/ AM-38 supercharger
Torsion bar, 7
85 mm F-30 (91 rounds) later replaced w/ 76 mm F-32
3x 7.62 mm DT machine guns (4,056 rounds)
Front/sides/rear of hull and turret: 100 mm
Top/Belly: 30 to 40 mm
Soviet Union (1941)
Heavy tank – Partial Mock-up Built
Even before the T-150 heavy tank entered trials in January 1941, several issues had already been noted and a new turret was designed. Nonetheless, this turret never left the drawing board. A second attempt was made during and after the T-150 trials, and the tank was named Object 222. After impressing the military and state officials, it was named KV-3. The excitement was short-lived, however. In April, heavier tanks, like the Object 223, were designed, and this latter project would eventually get the name KV-3 as well. The Object 222 was then meant to enter production in June 1941, under the name KV-6, but, due to the German invasion of the Soviet Union, this never happened.
The KV-1 heavy tank would officially enter production in February 1940, 9 months after the original request for production. Even so, by July, only 32 of the pre-series KV tanks were built, prefixed with the “U” index. The tanks had design issues, along with technical and production problems. The pressure from Stalin to adopt these unfinished tanks grew, and, in June 1940, with the “The Stalin Task”, the Council of People’s Commissars of the Soviet Union would order the increase of the yearly production quota of the KV to 230 units of both variants (130 standard KV-1 and 100 KV-2s with 152 mm howitzers). The Leningrad Kirov Plant (LKZ), barely able to keep up with the previous production rate, was ravished. Corners had to be cut in order to streamline and speed up production, while the tanks were still being tested and improved on the go. This cutting of corners would later come to bite the Soviet officials and factory designers in the back, as the KV-1 would prove to be unreliable and cumbersome on the battlefield.
The desire for heavier tanks based on the KV-1 appeared in May 1940, and by 17 July, the Main Directorate of Armored Forces (GABTU) and the People’s Commissariat of Heavy Engineering requested four new tanks from LKZ, more specifically the SKB-2 design bureau. Out of these four tanks, two were to pack 90 mm of armor, of which one armed with a 76 mm gun and one with an 85 mm gun. The other two were to have 100 mm of armor and also be equipped with a 76 mm and 85 mm gun respectively. The latter would become the T-220.
For the 90 mm armor tank with 76 mm gun, the chief designer, Military Engineer L.N. Pereverzev, part of the SKB-2 design bureau, was assigned to design it by August 1940. The new tank was indexed T-150, but the Object 150 and KV-150 names were also officially used. It was to be based entirely on the KV-1 in production, with only the necessary changes made. In order to add the extra 15 mm of armor all around the tank, it was necessary to equip it with a new engine, namely the 700 hp V-5 from Plant No.75. As the thickening of the armor was done outwards, the internal layout and components position of the KV-1 were kept the same. Reinforcements were added to the suspension to better deal with the extra mass, which reached 50.16 tonnes, compared to the 44 tonne KV-1 (autumn 1940). Lastly, and perhaps the largest external change on the T-150, was the addition of a large commander’s cupola, equipped with 6 periscopes and one rotating PTC periscope.
The first prototype was to be built and delivered to LKZ by the Izhora plant by 1 October, but due to overloading difficulties caused by the KV-1 production, the prototype was only delivered by 1 November. During November, after analysis by its designers, a new turret for the T-150 was designed, that would fix certain problems annotated, like the poor commander’s position to the right of the gun. In the new turret, the commander was moved to the back, inside the turret bustle, where he would have a better overview of the battlefield, with 8 periscopes instead of 6, and better communication with the crew. Another problem fixed was the removal of the gunshield above the mantlet, which on the T-150 prototype was poorly made and restricted gun depression. Despite these promising changes, it did not go past the blueprint stage.
Testing of the T-150 would begin on 14 January 1941 and end in February. During this period, several significant issues were discovered. Firstly, the T-150 weighed 50.16 tonnes, over 2 tonnes heavier than the 48 tonne threshold imposed by the GABTU. Secondly, the experimental V-5 engines would prove to be a complete disaster. The chief designer of Plant No.75, T. Chuptakhin, who was present at the trials, was not able to guarantee the operation of the engines installed on the T-150 and T-220 tanks. The T-150 would only operate for 24 hours or 199 km before its engine broke down. It was noted that when driving in high gears (3rd and 4th gear), the injected oil temperature would spike after just 5 minutes even in outside temperatures of 9-12º Celsius.
The turret would prove problematic as well, despite the issues originally being noticed in November. The commander’s cupola was too tall for observation while sitting down, but too low when standing up, forcing the commander to semi-squat in a very straining position. The other crewmembers in the turret were not spared of problems either. The loader, sat behind the commander and to the right of the gun, would be restricted from lifting shells from the left wall by DT machine gun ammunition boxes. The vast majority of the main gun shells were stored in small boxes, which were hard to open, cutting the loader’s hands and getting stuck on one-another. This decreased the rate of fire to 1-2 rounds per minute when loading from the boxes (from 5-7 rounds per minute maximum). Lastly, the gunshield above the mantlet was badly designed and only allowed for 3º of gun depression, instead of the 6.5º intended.
All in all, the T-150 performed as expected considering the rough circumstances, and many of the issues could be roughed up. Despite this, the GABTU and People’s Commissariat of Heavy Engineering were not satisfied with the result and demanded that the turret and engine problems be fixed.
Before the T-150 trials were even finished, a second attempt at improving the turret was made. Like the first time, the commander’s position was moved to the turret bustle, with a more streamlined cupola, which dropped the PTC rotating periscope but maintained the eight periscopes, as opposed to the T-150’s six. Other changes included the casting of the gun mantlet for faster production, removing the side turret wall gun port and decreasing the size of the gunshield. One of the more controversial changes was the adjusting of the side and rear wall armor to vertical angles, as opposed to 15° inwards. Otherwise, the design would use the same hull as the original T-150. The tank was indexed Object 222.
After review of the project by the GABTU and state authorities, the People’s Commissariat of Defence and the Central Committee of the Communist Party proposed accepting Object 222 into service and giving it the name KV-3. The name KV-3 had previously been used when describing the T-150. The question of propulsion was also raised, but after a commission formed on 21 February, Plant No.75 had to figure out the issues with its engines and make them usable by 10 April. To ensure that the engine would not overheat again, the cooling system of the Object 222 was reworked as well.
The Object 222 was still armed with the 76 mm F-32 gun, but with the same gun being introduced on the KV-1, it seemed like it would quickly become redundant. Thus, it was also proposed that the Object 222 (KV-3) was to be rearmed with the much more potent 76 mm F-34.
On 3 March 1941, a commission was formed, consisting of Military Engineers 2nd Rank I.A. Burtsev and I.A. Shpitanov, Military Engineer 3rd rank Kaulin, LKZ director I.M. Zaltsman, SKB-2 director J.Y. Kotin, director of LKZ 1st dept. A.Y. Lantsberg and NII-48 research institute engineers V. Dalle and A.P. Goryachev. The goal of the commission was to further assess the Object 222 and prepare it for prototype production. The commission reviewed the drawings of the tank as well as a wooden mock-up of the turret mounted on the hull of the KV-1. It was here that the lack of an angle on the side and rear plates was deemed as an issue, decreasing the overall armor protection. Other issues noted was the lack of an entry and exit hatch on the commander’s cupola and vulnerability of the pericopes from damage and enemy fire.
Nonetheless, the commission agreed on producing a turret as per the above in order to have it ready for testing by 1 April. Yet the commission would expect that, by the time of mass production, the turret walls would be angled again. According to the three representatives from LKZ, Zaltsman, Kotin and Lantsberg, the reasons for implementation of vertical walls were:
Improving crew working conditions;
Improving connections between the plates, especially for the roof plate;
Additionally, they claimed that the sloping brought no true advantages either. Mathematically, the equivalent armor thickness of a 90 mm plate angled at 15° is 93.17 mm, an insignificant gain considering the production complications.
After the commission, on 15 March, the Council of People’s Commissars of the Soviet Union and the Central Committee of the Communist Party gave decree No. 548-232§, which imposed that LKZ had to switch mass production to the KV-3 (Object 222) in August, with 55 units built in the first month, increasing to 105 in September, 110 through October and November, and 120 units in December, for a total of 500 KV-3 tanks in 1941.
The date of delivery was also pushed back after LKZ’s ‘complaints’, and the first prototype was to be delivered by 1 May, and testing to begin on 15 May. To meet this deadline, the Izhora plant had to deliver the experimental turret by 1 April, with LKZ having to deliver drawings of the experimental turret on 20 March, drawings of the hull by March 25 and drawings of the production turret by 10 April. Plant No.203 to deliver the KRSTB radio set and Plant No.69 to deliver optical sights for the DT machine guns.
The Object 222 (T-222/KV-3) was just a T-150 hull with a slightly modified turret. In turn, the T-150’s hull was just a KV-1 hull with a new engine and minor dimension changes due to the thicker armor. The frontal upper plate consisted of two parts, an angled ‘hood’ and a flatter portion, right in front of the driver and radio operator. On it was the headlight, driver’s vision port, and a 7.62 DT machine gun in a ball-mount. Above, on the top deck was a service hatch for the two crewmembers. The running gear consisted of a frontal idler, large rear sprocket, and 6 steel rimmed wheels, sprung by torsion bars, with three return rollers.
The general armor profile was of 90 mm all around, with the exception of the turret roof, which was 40 mm thick, and hull deck, which was 30 mm. With the new turret, the weight of the Object 222 was expected to be slightly higher than that of the T-150, at 51 to 52 tonnes.
The new turret differed greatly from the T-150’, but was heavily inspired by the November 1940 T-150 turret upgrade. The gun mantlet was a two-part cast type, and the gunshield was shorter, for improved gun elevation and depression angles. The design of the turret walls was altered as well, with larger flat side and rear plates and potentially a rear turret door, like on the KV-2 and T-220, though this is unconfirmed. The rear-facing 7.62 mm DT machine gun mount was kept, though the ball-mount design was changed as well. Other minor changes to the turret included strengthening around the gun mantlet side-front plate connection and the replacement of side gun port and vision slit with a small hatch.
The most important change was the relocation of the commander, to the back of the turret. The position of the T-150’s commander was noted as an issue already in November 1940, thus the first turret upgrade design also placed the commander in the back. Likewise, the trials of the T-150 criticized the position of the commander and suggested moving him to the rear. However, after the commission analysis of the Object 222 turret, it was not deemed as ideal. Additionally, the lack of an entry-exit hatch for the commander and no protection ring for the periscopes were also deemed as an issue. To fit the commander in the turret overhang, a large groove was made along the connection between the turret ring and the turret overhang bottom plate, to allow the commander to sit on.
The crew consisted of 5: commander, gunner, loader, driver, and radio operator. The commander sat in the turret bustle, from where he could communicate with the loader and gunner. For vision, he had a cupola with 8 periscopes. He would also operate the rear facing machine gun, should the situation call for it. The gunner sat to the left of the gun, and had his primary gun sight and a PTC rotating periscope for general vision. A second fixed periscope was placed on the side of the turret, like on most KV tanks. The loader sat to the right and rear of the gun, and would load shells from both sides of the turret walls and those stowed in the hull floor. He was no longer responsible for the rear-facing machine gun.
The positions of the crew in the hull was unchanged from the KV-1, with the driver in the center and the radio operator to his left. The radio was a KRSTB, an early version of the 10-RT radio, but it was possible to install the standard 71-TK-3 radio.
The engine of the Object 222 was to remain the V-5 engine, as on the T-150, but in a functional form and with a redesigned cooling system. The V-5 engine had been developed at Plant No.75 by boosting the V-2K 600 hp engine, which itself was an already boosted and unreliable variant of the V-2. The V-5 was a four-stroke 12-cylinder diesel engine outputting 700 hp. The fuel tank had a 700 liter capacity, offering the tank a range of 250 km or 10 work hours. Maximum speed was a mere 35 km/h on road and off-road, 15 to 20 km/h. The tank had a warranted distance between major breakdowns of 2,000 km.
Initially, the main armament was to remain the 76.2 mm F-32, as on the original T-150 and which just began incorporation on serially produced KV-1s, replacing the L-11 gun. But during discussions in February, it was proposed to rearm the Object 222 with the much more potent 76.2 mm F-34. The tank carried 114 shells for the 76 mm gun and 2900 rounds in 46 drums for the DT machine guns. The main difference between the F-32 and F-34 guns was the muzzle velocity and penetration. For example, the same shell, BR-350A (APHE) had 615 m/s muzzle velocity in the F-32 and 662 m/s in the F-34. Likewise, the OF-350 (HE) had 615 m/s muzzle velocity on the F-32 and 680 m/s on the F-34. The F-34 gun was mounted on the T-34 tank in early 1941, with the KV-1 adopting it only much later as the ZiS-5 gun.
Muzzle velocity (m/s)
Shell weight (kg)
The tank was armed with two 7.62 DT machine guns, one in the hull for the radio operator and one in the back of the turret. The KV-1 and T-150 also featured a coaxial machine gun, but it was dropped on the Object 222, as the commander was moved and due to the new gun mantlet.
Between 7-9 April, the LKZ heavy tank development programs were altered, as the need for more powerful heavy tanks was assessed. The KV-3 name would be given to a new tank, based on the up-armored chassis (120 mm frontal armor) of the Object 221, and named Object 223, as well as receiving an entirely new turret armed with the 107 mm ZiS-6. Furthermore, a 100-tonne tank was also requested, with 170 mm of frontal armor and also armed with the 107 mm ZiS-6 and was named KV-5 (Object 225). The LKZ factory was still meant to build a prototype and begin prototype production by June, but with three heavy tank developments ongoing simultaneously with tight deadlines. Based on the production quota report for LKZ, 500 KV-3 (Object 223) tanks should have been built from August 1941 to the end of the year.
On 5 May, Marshal G.I. Kulik and Lt. Gen. Y. Fedorenko came to the Central Committee of the Council of People’s Commissars of the Soviet Union, requesting the switch to the KV-6 (Object 222) as opposed to the KV-3 (Object 223). Historian Maxim Kolomiets also mentions here that the KV-6 was also armed with a flamethrower with 15 rounds (10 liters) and that the vehicle was actually the T-150, though that is improbable.
The situation worsened on 22 June 1941, when the Axis forces began Operation Barbarossa, the invasion of the Soviet Union. Thus, much of the military’s focus shifted to producing, maintaining, and improving existing tanks. Furthermore, by September, German forces were approaching the city of Leningrad and many SKB-2 engineers were evacuated or placed into military maintenance battalions. Those evacuated were sent to the Chelyabinsk Tractor Plant (ChTZ) which was renamed ChKZ (Chelyabinsk Kirov Plant) after this move. Work on the KV-4 and KV-5 would not resume, but the KV-3 would continue to see slow development until December, when it was finally canceled.
The Object 222, (KV-6) would be ordered to start production at ChTZ on 1 January 1942, with LKZ and NKTM officials providing a prototype, while ChTZ sends a team to LKZ to establish the technical details of the design and prepare for its production.
The first KV-3, the Object 222, was just a T-150 with a new turret. Unlike its predecessor, it was much more short-lived, damned by the design and developments of much heavier KV tanks. With hindsight, the Object 222 was a genuinely good design on paper, and a mature improvement of the KV-1. Sadly, the Object 222 remains overshadowed to this day by more ‘exciting’ designs, like the T-220 and Object 223, the latter KV-3. Only a turret mock-up was built, which was likely destroyed during the war.
Object 222 (T-222/KV-3/KV-6) Specifications
Dimensions (L-W-H) (approx.)
6.760 x 3.330 x 3.010 m
Total weight, battle-ready
51 – 52 tonnes
5 (Commander, gunner, loader, driver, radio operator)
V-5 12-cylinder diesel, outputting 700 hp.
Torsion bar, 6
76.2 mm F-32 or F-34
3x 7.62 mm DT machine guns
Front/sides/rear of hull and turret: 90 mm
Top/Belly: 30 to 40 mm
Soviet Union (1940-1943)
Heavy Tank – 1 Prototype Built
The KV-150, or more commonly named T-150, was an attempt to improve the armor of the KV-1 even before the KV-1 entered mass production. With 90 mm of armor all around and a 700 hp engine, it could have been a better option had it not been for some critical events during its development phase. It was, however, groundbreaking in what would become a series of KV heavy tanks, and the single prototype saw combat service until the end of 1943.
As one of the most iconic and recognizable tanks of the Second World War, the KV-1 (or simply KV, acronym for the People’s Commissar of Defense for the Soviet Union, Kliment Voroshilov), proved to have unmatched armor and a very potent gun at the start of the German invasion of the Soviet Union, on 22 June, 1941. It had been developed in the late 1930s and tested in combat alongside its 2 much larger competitors, the SMK and T-100, during the Winter War. As the latter 2 followed a much more complex and archaic breakthrough tank philosophy, namely multi-turreted “landships”, the KV-1 (at the time U-0) would be selected for further development. It was created at the Kirov Leningrad Plant (LKZ), where the previous T-28 and its own competitor, the SMK, were designed and built.
By 19 December, 1939, production of 50 KVs was ordered, with mass production to begin in 1941. But, during this time, the ugly side of the vehicle started to come to light. Truth is that, by that time, the KV was far from ready for production, and dozens of mechanical problems, mostly caused by the heavy weight, had to be sorted out. However, due to Stalin’s personal involvement and pressure on the project, the KV entered preseries production in February 1940, which were indexed with a “U” prefix. These differed from vehicle to vehicle and were tested thoroughly to diagnose any issues.
Naturally, Stalin’s patience would not last, and in June 1940, in what would be called “The Stalin Task”, a decree from the Council of People’s Commissars of the Soviet Union would increase the yearly production quota of the KV to 230 units of both variants (130 standard KV-1 and 100 KV-2s with 152 mm howitzers). This immediate increase in production strained the LKZ plant into mass producing what was effectively an unfinished tank. Naturally, corners and compromises had to be cut over all fields in order to streamline production and cut costs. As some KVs were built, others were still vigorously tested, and results showed that the reliability of the gearbox and transmission were poor. Although changes were made, this aspect would become the bane of the KV-1’s existence. From February to July, 32 KV tanks had been built, and production would increase to 20 during the month of August and 32 during September.
As early as May 1940, before the KV-1 even entered its shy mass production, the topic of improving the armor of the KV was discussed both by the GABTU (Main Directorate of Armored Forces) and by the People’s Commissariat of Heavy Engineering, where the LKZ plant was represented at. First mentions of thickening the KV tank’s armor came on 11 June, which claimed the need to up-armor the tank to armor between 90 and 100 mm. Furthermore, on 17 July, 1940, the Council of People’s Commissars of the Soviet Union adopted decree No. 1288-495cc, which stated:
By November 1, 1940, the Kirov Plant will produce two KV tanks with 90 mm of armor: one with a 76 mm F-32 gun, the other with an 85 mm gun. The Izhora Plant will deliver one hull at the end of October, the production of the tank is scheduled to be completed by November 5. The second hull will be made by November 5th.
By December 1, 1940, the Kirov Plant will produce two KV tanks with 100 mm of armor: one with a 76 mm F-32 gun, the other with a 85 mm gun. One hull will be delivered by the end of October and by the end in November.
In comparison to its predecessor, the KV-1, as being built in summer-autumn 1940, had 90 mm around the gun mantlet and 75 mm all around. These were exquisite levels of armor not just for Soviet tank standards, but also internationally, being able to withstand most anti-tank guns. It also put the weight of the KV at 44 tonnes, already a tonne increase from the U-0. The weight of the KV would keep on increasing, peaking at 47.5 tonnes by 1941.
Regarding the armament mentioned in the decree, the KV-1 was equipped, as a stopgap measure, with the L-11 76 mm gun until mass production of the more potent 76 mm F-32 could begin. As for the 85 mm gun, it was likely to be the F-30 gun developed by V.G. Grabin at plant No. 92 in Gorky, based on the 85 mm M1939 52-K. However, it is noteworthy that only one such gun had been built, and its testing had yet to conclude.
The first obstacle that the up-armored KV faced was the KV itself. By July, the design bureau tasked with its development, SKB-2 and the entire LKZ factory were busy producing and improving the KV, with little room to spare for a new development. The situation was worsened by the delayed delivery of the tank requirements from the military to SKB-2.
In August, head of the SKB-2’s design bureau, J.Y. Kotin, made two teams for the development of the two tanks. The 90 mm-armor KV was to be designed by a team led by Military Engineer L.N. Pereverzev and indexed as T-150 or Object 150 / KV-150. All 3 names were used in documents. For the sake of simplicity and consistency, it will be called T-150 in the article, with the exception of direct document translations. At this point, Pereverzev was still rather new to SKB-2, having just graduated from the Military Academy of Mechanization and Motorisation of the Red Army in 1939, and had only worked on the KV-1.
For designing the 100 mm-armored KV, the more experienced L.E. Sychev was appointed as chief designer. This variant would be indexed T-220 or Object 220 / KV-220. Sychev was a tank design veteran. He had worked on his bachelors at SKB-2 and then began his career in the same place, working on the T-28, SMK, and KV-1.
Once SKB-2 had sent over the documents (likely in September 1940) to the Izhora plant, the T-150 faced another issue. The Izhora plant was working at a very high capacity trying to increase its KV tank output. The 4 prototype KVs were to be built at Hall No.2, where 4 KV tanks were already being built at the same time. This meant that the October 1 deadline for the T-150 was missed, but not by much.
The Izhora plant delivered the hull of the T-150 and a turret on November 1 and LKZ completed the prototype by December. The T-220 was completed shortly after.
In November, during the latter stages of the development of the T-150, a new turret was proposed. It moved the commander to the rear of the turret and gave him a low cupola with a PTC rotating periscope. Other aspects remained the same as on the original T-150 turret. Only a simple sketch of it was done, with a slightly more detailed drawing of the new commander’s position. It was not considered, but it was used as the basis of the Object 222’s turret, which was essentially the T-150 with a completely new turret .
Object 221 – The T-150’s Bigger Brother
As per the request from 17 July, 1940, two tanks were supposed to be built with 90 mm armor, one with a 76 mm gun and one with an 85 mm gun. The first became the T-150, however, the latter had a more troubled development. When researching about the mounting of a 85 mm gun on the chassis of the KV-1, it was realized that it would not fit in the standard KV turret and a larger turret combined with additional armor would require a longer hull. This meant that both the 90 mm and 100 mm variants armed with an 85 mm gun would receive a longer hull, by one roadwheel (a total of seven). The 100 mm armored variant armed with the 85 mm gun became the T-220.
The 90 mm variant was named Object 221 or T-221. It was intended to mount the same turret and 85 mm F-30 gun as the T-220. However, there were serious delays, and the Izhora plant only managed to deliver hull components for the T-221 by 10 February 1941, and the F-30 gun and turret were not ready. On 19 February, Marshall of the Soviet Union G.I. Kulik proposed that the 76 mm F-27 gun be mounted inside a KV-1 turret instead, but nothing was done. The Object 221 remained abandoned until April, when it was used as the basis for the KV-3 (Object 223), though 30 mm of extra frontal armor were required for it to reach the specified armor thickness.
For the most part, the T-150 was identical to the KV-1. As the additional 15 mm of armor were added on the outside of the hull, the internal layout for the crew was unchanged. The main armament was, as requested, a 76.2 mm F-32 gun, coaxially paired with a 7.62 mm DT machine gun to the right of the main gun, with another DT machine gun at the rear of the turret and one in the hull, next to the driver. Both machine guns were mounted in ball mounts.
The weight of the T-150 reached 50.16 tonnes, around 6 tonnes heavier than a KV, and went past the weight threshold by over 2 tonnes. Due to the increased weight, the suspension was reinforced. Otherwise, the hull remained identical to that of the KV-1, with front idler, large rear sprocket and 6 steel-rimmed roadwheels.
The front of the tank had the same features as the KV-1, with 2 tow hooks on the lower plate, a single driver viewport in the center of the upper plate, with a driving light to its right and ball mounted machine gun to its left.
The turret was essentially a KV-1 turret with thicker armor, but certain changes were made to accommodate the commander’s cupola. It was fixed in place and of cast construction. At the front, a fully rotating PTC periscope was mounted, with 6 other triplex periscopes around the cupola. The commander’s cupola likely lacked a service hatch, meaning that the commander and loader would likely have to share a hatch. The turret also featured the standard KV-1 vision devices, a PTC rotating periscope for the gunner and another periscope to the side and 2 facing the rear. Direct vision slits were provided over the machine gun ports. This meant that, on paper, the T-150 offered better vision for the crew than the KV-1. The driver’s vision systems were not changed.
The main novelty of the T-150 was its 90 mm armor all around the turret and hull. The turret deck, hull deck and hull belly were 30-40 mm thick. The commander’s cupola was rather large, but was also 90 mm all around and, thus, was not a weak spot. Frontally, this was a 20% increase in raw thickness over the KV-1 in most areas.
The crew of the T-150 was the same as that on the KV-1, with 5 men: driver, radio operator/bow machine gunner, commander, gunner, and loader.
The commander was seated to the right of the gun, where he would be able to observe the battlefield from his cupola. He was also tasked with loading the coaxial DT machine gun on his side. The gunner sat on the other side of the gun, to the left of the turret. He would aim and fire the gun via a TOD sight. He had a rotating PTC and fixed periscope for external vision. He was able to rotate the turret via an electric system but also with a hand crank. Behind the commander sat the loader, on a removable seat (for easier maintenance/loading). He would load the main gun with shells stored on the side turret walls and in cases on the hull floor. He would also operate the rare turret machine gun, should the situation require.
In the center of the hull sat the driver, and to his left the radio operator, who also manned the bow DT machine gun. The radio was mounted underneath the frontal plate.
Engine and Propulsion
The engine installed on the T-150 (and T-220) was the four-stroke V-5 diesel, 12-cylinder in V-config with an output of 700 hp. It was essentially a boosted V-2K (600 hp), which itself was a boosted variant of the V-2. The main problem was that the V-2K was unreliable and barely guaranteed to work for up to 100 hours. Consequently, the V-5 was even less reliable. So much so that, during trials, the chief designer from Plant No.75 could not guarantee the function of the engines on the T-150 and T-220. Combined with the poor design of the engine’s cooling system done by SKB-2 engineers, the engine would have several major issues during the trials and only worked for 199 km, or 24 hours.
The fuel tank capacity remained the same as on the KV-1, at 615 liters, which reduced the range to 220 km (on roads).
The main armament on the T-150 was the 76.2 mm F-32 gun. It was developed by Plant No.92 in Gorky in the late 1930s and was tested on the BT-7. It could fire BR-350A and BR-350B (APHE), BR-350SP (AP), and OF-350M (HE). The shell weight varied between 6.2 kg and 6.78 kg, depending on the type. The muzzle velocity was between 613 and 621 m/s (figures vary depending on the source consulted). In January 1941, the KV-1 would enter production with the F-32 gun. It was ballistically very similar to the L-11 it was replacing on the KV-1, while the T-34 would receive the far more potent F-34 76 mm gun the same year.
For proximity and anti-infantry defense, three 7.62 mm DT machine guns were mounted, one coaxially, to the right of the gun, which could be used for ranging closer targets (muzzle velocity around 840 m/s). The front facing machine gun in the bow was for suppression of infantry and the machine gun in the rear of the turret was for defense against flanking infantry.
On 14 January 1941, the People’s Commissariats of Defence and People’s Commissariats of Heavy Engineering requested that the T-150 and T-220 be tested at the LKZ proving grounds. A commission, headed by the Military Engineer 1st Rank Glukhov and with representatives from the GABTU, would monitor the testing of the tanks. According to the commission for field testing, the following goals were intended.
Determining the tactical and technical characteristics of the tank.
Identifying the shortcomings in the designs and their elimination prior to mass production.
Judging whether it is possible to conduct military tests.
Accumulating data for operating and repairing the tanks.
The tests would begin the following day on both tanks. During this time, several issues were quickly identified. On 25 January, the two prototype tanks were weighed, with the T-150 weighing 50,160 kg and the T-220, 62,700 kg. The problem here was that the GABTU specifically requested the T-150 to weigh a maximum of 48 tonnes and the T-220 56 tonnes. A report written by Military Engineer 1st Rank Glukhov on 28 January to the Head of Armored Department of the GABTU, Military Engineer 1st Rank Korobov, in the midst of the trials, showed that the commander’s cupola was poorly made (the observation devices were located too high, vision was inconvenient) and was placed in the loader’s position, who is not in command of the tank. Comically, the Chief Designer of Plant No.75, T. Chuptakhin, who was present at the trials, was not able to guarantee the operation of the engines installed on the T-150 and T-220 tanks. One of Glukhov’s reports included the following passage:
“The T-150 tank, after replacing the engine that failed during the factory run on 21 January, has not yet been brought back to the accepted state required by the Quality Control Department and military representatives.”
The gunshield was crudely made and provides only 3º of gun depression, instead of the 6.5º, as specified by the drawings.”
Due to the breakdown of the experimental V-5 engine provided by Factory No.75, the T-150 traveled only 199 km, or 24 work hours. Several issues were found and once again reported by Glukhov:
“The engine’s oil cooling system prevents the tank from driving at high speeds in the 3rd and 4th gear (at an outside temperature of 9° to 12°, the temperature of the injected engine oil increased rapidly after 5 minutes of motion in 3rd and 4th gears). Normal operation of the engine (inlet oil temp. 70°-80°). Due to the poor design of the cooling system, driving trials on the T-150 would cease.”
Instead, focus shifted towards firing trials, especially relevant as the F-32 gun had just replaced the L-11 gun on the KV-1’s production lines. Firing while stationary and firing during short stops went as expected (considering the 4-5 second aiming time), but firing on the move was unsatisfactory, though many of these results were entirely based on circumstances such as terrain and gunner skill, and the gunner conducting the trials, although experienced, was still not entirely familiar with the gun and tank.
Simultaneously, loading times were measured, depending on where the rounds were stowed. When loading shells from the right turret side (9 rounds), 5-7 rounds per minute were sustained. When loading shells from the left side of the turret (9 rounds), the rate of fire dropped to 3 rounds per minute, as the loader had to lean to the other side of the turret. The situation got worse when loading via casings that held 3 rounds. These would have to be lifted up and opened before the shells could be loaded in. This process slowed the rate of fire to 1-2 rounds per minute. In contrast, although not practical, when the shells were simply laid on the floor, 11 rounds per minute could be sustained. Furthermore, the ammunition cases, stowed on the hull floor, would often catch on one another when attempting to lift them, and on 6 separate instances, rounds were jammed inside. The sharp edges of the cases also injured the loader’s hands. Consequently, the commission noted that the ammunition stowage system had to be reworked.
Several issues had been noted with the crew’s positions as well. Firstly, the commander’s seat (combined with the cupola) were criticized for being fixed in place, preventing the commander from viewing out of the periscopes while seated. Likewise, he could not stand, as there was no room, but rather the commander had to stand with his knees slightly bent, in a semi-squatting position (naturally very tiring) to see out of the cupola. Other complaints included that he had to turn very frequently to communicate to the rest of the crew and he was also charged with loading the coaxial DT machine gun.
The gunner’s position also required improvements. The sight was deemed too far forward and slightly to the left, and the seat required more adjustment. The footrests and pedals required work as well. The knee would be bent too much. Additionally, the heel rest was too far down, requiring the gunner to keep his heel in the air in order to maintain his toes on the pedal, or overextend his ankle, both very tedious tasks.
The loader, aside from the aforementioned loading problems, would have his workspace cramped up by the commander’s seat, only 6-8 ammunition cases were easily accessible, and the machine gun drums were in the way when lifting rounds from the left turret wall.
Testing of the T-150 was concluded on 14 February. The trial results were reported back to the GABTU and People’s Commissariat of Heavy Engineering. Although the aforementioned issues were noted (and such problems were understandable for a prototype vehicle), it was decided to move forwards with the T-150 project, but in an altered form. Based on reports during this time, both the T-150 and T-220 were sometimes called KV-3. The more common use of this name came with the Object 222 and later with the Object 223, the KV-3 commonly known today.
On 21 February, a commission was made for analyzing the reason for the failure of Plant No.75’s engines on both the T-150 and T-220, and estimating a time of arrival of the fixed engines. The deadline was set for 10 April.
During the same period, between 18 and 24 February, Plant No.75 tested the V-5 engine on KV tank U-21, and it broke down once again, after 40 hours of operation.
On 1 March, the T-150 was officially canceled. The V-5 engine was still unrefined, and the tank was deemed to have several issues necessary to fix, but there was no point in doing so. Instead focus was shifted to the Object 222, which was based on the T-150.
Many of the issues of the T-150 that were discovered during the factory trials were identified far earlier on. As a result, the SKB-2’s design bureau started work on a new tank in January-February, 1941 to fix these issues. The new tank, which used the same hull as the T-150, would be indexed Object 222. Originally, the differences between it and its predecessor consisted of a new cooling system and a new turret. This new turret was slightly larger, had flat sides (as opposed to 15° angled inwards on the KV-1 and T-150), and a slightly sloped frontal plate. The commander and his cupola were moved to the back of the turret as well.
By the end of February, the People’s Commissariat of Defence and the Central Committee of the Communist Party proposed accepting the KV-3 (Object 222) into service. Additionally, the topic of improving the main armament to the 76.2 mm F-34 was also raised. This gun had improved ballistics over the previous F-32 on the T-150. As for the propulsion, the tank was to use the same V-5 engine.
On 3 March 1941, a commission was formed, consisting of Military Engineers 2nd Rank I.A. Burtsev and I.A. Shpitanov, Military Engineer 3rd Rank Kaulin, LKZ Director I.M. Zaltsman, SKB-2 Director J.Y. Kotin, Director of LKZ 1st Dept. A.Y. Lantsberg, and NII-48 research institute engineers V. Dalle and A.P. Goryachev. Together, they reviewed the drawings and a full-scale wooden mock-up turret of the Object 222 turret mounted on a KV-1 (for simplicity’s sake). Turret armor would have been 90 mm all around and 40 mm on top. Several issues were identified, such as the flat turret walls, which were deemed to decrease protection, the less than ideal commander position, and the lack of hatch on the cupola for the commander. Despite these issues, the commission concluded that the turret should be built anyways, since there was little time to redesign it.
On March 15, the Council of People’s Commissars of the Soviet Union and the Central Committee of the Communist Party gave decree No. 548-232§, which imposed that LKZ had to switch mass production to the KV-3 (Object 222) in June.
The officials were confident that, by then, the new turret could be tested and refined. As for the T-150’s hull, with the new cooling system and properly tuned V-5 engine, it would run smoothly, as it was essentially just an up-armored KV-1 hull.
German Heavy Tanks
However, 4 days earlier, on 11 March, the Soviet Intelligence services had just released a report regarding the German Reich’s tank developments. Notes of several heavy tanks were highlighted, notably three new tanks that were under development. One of them was labeled Mark V, was to weigh 36 tonnes, and be armed with a 75 mm gun. The Mark VI was to weigh 45 tonnes and be armed with a 75 mm gun, and, finally, the Mark VII was to weigh 90 tonnes and be armed with a 105 mm. The first 2 tanks can be confidently identified now as the VK.30.01(H) and VK.36.01(H) and early Tiger mentions. But the latter can only be described as some early proposal to what would become the Pz.Kpfw.VII Löwe, which was first mentioned officially in German documents in November 1941.
This new German heavy tank was nearly double in weight of the KV-3 and considerably above the T-220. The 105 mm gun was far more alarming than the 76.2 mm F-34 that the KV-3 (Object 222) was to be equipped with and the 85 mm F-30 on the T-220.
On 21 March, the GABTU requested the urgent development of a new heavy tank from SKB-2 at LKZ, capable of matching the supposed German heavy tanks. It was to weigh up to 72 tonnes, have 130 mm of frontal armor, and be armed with the 107 mm ZiS-6 gun. It was indexed Object 224 / KV-4. On April 7, the GABTU would rework their approach, requesting that the KV-3 be based on the T-220 (Object 220) and armed with a 107 mm ZiS-6 and weigh 68 tonnes. The new KV-3 was indexed Object 223. An even heavier tank was also conceived, the KV-5 (Object 225), with 170 mm of frontal armor and 150 mm of side and rear armor, weighing over 100 tonnes.
After the invasion of the Soviet Union and the Siege of Leningrad in September, much of the SKB-2’s design bureau and its prototype tanks were evacuated to the ChTZ plant in Chelyabinsk, which was now renamed ChKZ, or Tankograd.
Most of the work on the heavy tanks was stopped in order to focus on more sensible topics at ChKZ. The only exception was the Object 222 (which had now been renamed to KV-6) and the Object 223 (KV-3). The GABTU was against the KV-6 and insisted on improving the armor of the T-150 to 120 mm and adding a new ZiS-5 gun. These were the last efforts on these tanks. The Object 223 (KV-3) progressed until December 1941.
These experimental tanks were incredibly expensive. A letter sent on 30 May 1941 to Military Engineer 1st Rank Korobov by A.Y. Lantsberg described the development costs of the major KV series of heavy tanks (Object 150, Object 220, Object 221, Object 212, Object 218, Object 223, Object 224, and Object 225). These had a total development sum of 5,350,000 rubles. The T-150 project would cost in total 1,500,000 rubles. In perspective, a KV-1 in 1941 would cost between 523,000 to 635,000 rubles.
Stage of T-150 Development
Price (thousands of rubles)
Prototype construction and factory trials
Proving ground trials
Drawing correction after trials
Repair of prototypes and improvements
Source: CAMO RF 38-11355-101
One of the more sensible alternatives was the KV-1E (the E is a post-war addition and derives from the Russian word meaning shield or screens), a regular production KV-1 with 30 mm to 25 mm additional armor plates, making the protection of the KV-1E superior to that of the T-150. The idea of the KV-1 with appliqué armor appeared on 19 June, 1941 and would be given to troops by July.
The work on Object 222, Object 223, Object 224, and Object 225 tanks did not mark the end of the T-150 prototype’s career. During the month of June 1941, the T-150 was retested with a worked-out V-5 engine and improved cooling system. This time, it traveled 2,237 km by 19 June. In total, 5 different V-5 engines had been installed on the tank during its trials. Amongst the issues noted were:
Oil leaks from the gearbox’s primary oil retainer.
Teeth from the 3rd and 4th gear as well as conical gear were sheared off.
Collar bracket of the 2nd and 4th gears were worn out by 4 mm.
2 rubber shock absorbers had been destroyed.
Paper fuel filters failed
Several new production methods had also worked well, such as hot-pressing the torsion bar with the torsion arm together, and the gearbox casing, made out of recycled aluminium, did not show sign of damage or failures after 1671 km.
T-150 in Combat
As the Soviet Union was suffering rapid defeats against the Axis powers, prototype tanks were pressed into service. The T-150 would be no exception. It entered service with the 123rd Tank Brigade on 11 October 1941. A week later, on 18 October, the brigade, part of the 8th Army, fought around Neva Dubrovka and later crossed the Neva river. On 18 May 1943, the T-150, by then part of the 31st Guards Heavy Tank Regiment, was listed as knocked out beyond repair. But the need for tanks was there and it was sent to Plant No.371 for repairs and entered service with the same regiment in July. The commander was Guards Junior Lieutenant I.A. Kuksin and driver-mechanic was Technician-Lieutenant M.I. Shinalsky and the tank received the number 220 and callsign “Som” (Catfish).
Shortly after, Kuksin’s tank would partake in the Mga Offensive or Third Battle of Lake Ladova, and on 22 July 1943, the 31st Guards Heavy Tank Regiment, alongside 63rd Guards Rifle Division, engaged enemy forces south-east of Leningrad. During the fighting between July 22 and August 6, the 31st Guards Heavy Tank Regiment recorded kills of 10 enemy tanks (allegedly 5 Tiger tanks, 3 Panzer IVs, and 2 Panzer IIIs), 10 pillboxes, 34 foxholes, and 750 enemy personnel. Kuksin’s T-150 and his crew also performed well. During this period, they recorded the destruction of 5 foxholes, 2 light machine gun posts destroyed, and 36 soldiers. Their tank was also hit in the track and immobilized, yet the crew managed to get the track together and continue fighting. The tank held its position for 4 days, for which Kuksin and his crew received the Order of the Red Star.
On 12 August, the Regiment was assigned, with the 73rd Marine Rifle brigade, to capture the village of Anenskoye. The 1st and 4th companies attacked on 18 August at 04:55. The companies suffered heavy losses and, by 06:00, 9 out of the 10 tanks were taken out of battle, with only tank 206 being in working order. Amongst these casulties suffered on that day, the T-150 was one of them. Junior Lieutenant I.A. Kuksin, gunner Senior Sergeant A.S. Yurdin, driver Technician-Lieutenant M.I. Shinalsky, and loader Guards Seargant I.M. Brezhak were killed in action on 18 August and the T-150 was sent back to Plant No.371 for repairs.
Alternatively, a document dated 18 November 1943 shows that a new driver was assigned to the T-150 (noted as KV No.T-150, raising the question as to if the T-150 was ever given number “220”), and was still commanded by Kuksin.
It is worth highlighting that the T-220 also saw combat service, but its new turret and 85 mm F-30 gun were replaced with a regular KV-1 turret. The tank was knocked out during the defense of Leningrad.
The T-150 (KV-150 / Object 150) was, on paper, a minor upgrade to the KV-1, with just 15 mm of additional frontal armor, a more powerful 700 hp engine, and a new commander’s cupola. While the implementation of these changes proved problematic at first, the T-150 proved to be a very important step towards the design of even larger and heavier KV tanks. These ultimately proved to be a waste of money, time, and resources, assets which the Soviet tank industry did not have, especially with the Axis invasion. Like many Soviet pre-war prototypes and its larger brother, the T-220, the T-150 prototype saw combat service well into 1943, but what happened after is unknown.
T-150 / KV-150 / Object 150 Specifications
Dimensions (L-W-H) (approx.)
6.76 x 3.33 x 3.01 m
Total weight, battle-ready
5 (Commander, gunner, loader, driver, radio operator)
V-5 12-cylinder diesel, outputting 700 hp.
Torsion bar, 6
76.2 mm F-32
3x 7.62 mm DT machine guns
Front/sides/rear of hull and turret: 90 mm
Top/Belly: 30 to 40 mm
Just months after the IS-2 began production, work began on developing a new heavy tank to replace it down the line. Engineer N. F. Shashmurin and his team envisioned an unusual tank, meant as a direct IS-2 upgrade, the IS-M. The most notable aspects of Shashmurin’s design were the large-diameter road wheels and the rear mounted turret. However, his project was not taken into consideration and was short-lived, although it did pave the way to the IS-6, which used some of its features.
Shashmurin and the IS
Tank designers are usually overlooked in the popular imagination, and those few acknowledged are usually limited to the likes of Ferdinand Porsche or Alexander A. Morozov. Even when limited to Soviet heavy tanks, the names of Nikolai L. Dukhov and Joseph Y. Kotin overshadow the others. Yet Nikolai Fedorovich Shashmurin was the man behind the creation of one of the USSR’s greatest war-winning tanks, the IS-2.
Born in 1910 in what at the time was called St. Petersburg (to be renamed Leningrad in 1924), Nikolai Fedorovich Shashmurin started his engineering studies at the Leningrad Polytechnic Institute in 1930 and graduated in 1936. By 1937, he had started to work at LKZ (Leningrad Kirov Plant) as an engineer for the SKB-2 design bureau. Before the war, he would work on the T-28 medium tank and create the torsion bar suspension system (T-28 No.1552) fitted on the SMK and U-0 (first KV-1 prototype), a system which would be implemented further on all future Soviet heavy tanks and self-propelled guns. Additionally, he developed gearboxes for the KV-1 (his gearbox would be dropped in favor of Dukhov’s infamous gearbox which would haunt the KV-1 for its entire service life), KV-220, KV-3, and even his own design for the KV-4 program.
With the beginning of the German siege of Leningrad in 1941, the LKZ (Leningrad Kirov Factory), specifically SKB-2 engineers, were evacuated to ChTZ (Chelyabinsk Tractor Plant) in Chelyabinsk (near the Ural Mountains), renamed ChKZ (Chelyabinsk Kirov Plant) a few weeks later. At Chelyabinsk, Shashmurin would develop the gearbox of the KV-1S and, after N. V. Tseits’ death in summer 1942, he became the head engineer for the KV-13 (at the time called IS-1), a vehicle which he did not like. Nonetheless, he would build upon it, and by May 1943, he had designed a new variant, equipped with an 85 mm D-5T gun specifically for the task of penetrating the German Tiger I, mated to a new hull. This was the Object 237 (at the time named IS-3), which would be adopted in service in September 1943 as the IS.
In parallel, Shashmurin designed the Object 238, meant to fit the new 85 mm S-31 gun in the KV-1S, but it was unsuccessful due to the cramped conditions within the turret. Production of the IS-1 started in November of that year, but it would not last long, as, by May 1943, work began on fitting the IS with the 122 mm D-25T gun, and by December 1943, the Object 240 would enter service as the IS-2. The mounting of such a powerful high-caliber gun was unprecedented in Soviet heavy tanks, which normally had similar, if not the same, guns as medium tanks.
Improving the IS-2
Extensive testing of the IS-2 was done at the NIBT (38th Research Test Institute of Armored Vehicle) proving grounds at Kubinka in January and February 1944, where it was concluded that the armor of the tank was not sufficient. Most notably, the “stepped” frontal hull was considered a weak spot, and it was proposed that the frontal hull should be made out of one angled plate.
Even after the first IS combat engagements, it became clear that, with the introduction of the German Panther tank, armed with a 75 mm KwK 42 L/70 (which could pierce the frontal armor of the IS heavy tanks) that the IS was insufficient. As early as September 1943, General Fedorenko (Head of the Armored Vehicle Directorate of the Red Army) would send a letter to Stalin, requesting the thickening of the IS armor and increasing its weight to 55-60 tonnes.
Additionally, in November 1943, the technical requirements for a new heavy tank were set by the GABTU (Main Directorate of Armored Forces). It was to have a mass of 55 tonnes, crew of 5, 160-200 mm of armor(frontal turret and hull), 800-1,000 hp engine, and a 122 or 152 mm gun. Speed was to be at least 35 km/h. These requirements would be laid down at the ChKZ plant on 3 December (10 December according to other sources) by factory director I.M. Saltzman.
The ChKZ SKB-2 design bureau, headed by N.L. Dukhov, had already worked on a new heavy tank since July, with its own funds. It was the 56-tonne K tank. The project was named Object 701.
However, on 21 March 1944, the GABTU changed the technical requirements. The weight was lowered to 55-56 tonnes, armament was a 122 mm gun with a muzzle velocity of 1,000 m/s, and 30 to 40 rounds had to be carried. The engine was to have a 1,000 hp output and allow for 40 km/h top speed. Armor thickness was not specified, instead, it was to be immune frontally to the Panther’s 75 mm KwK 42 L/70 and the 88 mm PaK 43/2 L/71 of the Ferdinand/Elefant.
These changes forced the reworking of the existing Object 701, but a green light was given the same month to produce 2 prototypes, leading to the IS-4 tank’s long development, with the first prototype, the Object 701-0, being built in May 1944.
At the same time as the developments at SKB-2, the other design institution at ChKZ, Factory No.100, also worked on their own tanks based on the same requirements. Headed by J.Y. Kotin, their approach was different to that of SKB-2. Instead of designing a new tank, they focused on a deep modernization based on the IS-2. By 18 April 1944, Factory No.100 would present its initial designs. Again, 2 models were built, one with a frontal plate separated into 3 parts (as on the first K tank) and one with a UFO-shaped hull, akin to the Object 279, designed and built decades later. Despite the increased protection, both variants had the same weight as the IS-2, 46 tonnes.
A document dated 8 April 1944, ordered J.Y. Kotin and his team to develop an upgraded variant of the IS-2 and subsequent SPGs over a 3-month period. The improvements should have included, but not been limited to, strengthened the armor protection, transmission, and chassis.
This would likely trigger the development of a new IS-2 modernisation, based on the requirements from 21 March. The design was to be less ‘radical’ and closer to the IS-2, but some very big changes were made. The tank would be called the breakthrough tank IS-M, the M standing for модернизация, meaning ‘modernisation’.
Sources do not agree exactly when development started, some arguing March, whereas others early April 1944. Nonetheless, N.F. Shashmurin was head of the project. While some design elements were taken from the previous upgraded designs, the main change was moving the turret to the rear of the hull, creating a very unique tank. A drawing of the tank would be made by Dobrovolsky. Who he was is so far unknown.
The design of the IS-M was peculiar and unorthodox. The entire upper hull was made from several stamped steel plates, slightly angled inwards, with both the front and rear angled heavily. These were welded to the lower hull, which, while still mostly flat, had angled corners for extra weight saving. In addition to the main variant, a second variant was drawn out, with standard IS running gear. An SPG version was drawn as well, although only with very superficial details.
The IS-style turret was mounted at the rear of the hull, which allowed for very little gun overhang, decreasing the chance of the gun getting damaged in tight places such as forests and cities, or steep maneuvers, such as trenchcrossing. Despite its general shape being similar to the turret of the IS, several key components had been done away with, such as the big commander cupola or air vent.
The engine was to be an M-40 aviation engine, equipped with 4 TK-88 turbochargers. The displacement was of 61.07 l and had an output of 1,200 hp. Other sources claim it was a modified variant of the standard V-2-IS, such as the V-11 or V-16, yet these would only output between 500 and 700 hp, far less than the 800 to 1,000 hp specified. The M-40 engine was based on an aviation engine, thus could run on both diesel and kerosene. Whatever the engine was, it had a 10 h running time. The powerplant was kept inside an own compartment in the center of the hull, protecting the fighting compartiment and ammunition, consequently isolating the driver. Fuel tank was in the front, to the right of the driver. As the sprocket remained to the rear of the hull, the entire braking and final drive ensemble was kept at the rear, as on the original IS. However, this meant that the gearbox and driveshaft ran through the floor of the crew compartment. The transmission was likely offered in 2 variations, electromechanical, very similar to that on the Ferdinand/Elefant, or a conventional mechanical one. The gearbox was of planetary type.
For access to these components, the rear engine plate could be opened and rested on the hinges, for access to the final drive and brakes. The roof of the engine compartment was also removable, and had one engine access hatch, 4 air vents and 4 air purification filters.
Two different running gear options were presented, one with 6 large-diameter road wheels, which allowed the returning track to rest on them, or 6 IS road wheels with 3 return rollers. The large road wheels would offer improved mobility over very muddy terrain, where smaller road wheels would clog up with mud. Additionally, they removed the need for return rollers. In turn, the standard IS wheel layout was already in use on various IS and KV series of tanks, resulting in a cheaper and smarter logistic choice. In both variations, the wheels were sprung by torsion bars.
The crew was larger than on the IS-2, with 5 men; a commander, gunner, loader, driver, and radio operator. The commander sat in the left corner of the turret. He had a low profile cupola equipped with 2 opposite facing periscopes for vision. Sat in front of him was the gunner, who operated the main gun. He had the main gun sight for vision and an extra, fully rotating periscope for a better field of view. Opposite him, to the right of the gun, sat the loader. He had to load the 2-part ammunition gun, as well as assist the commander in various tasks. For entry and exit, he had his own hatch with a periscope. The driver sat in the front of the hull, from where he would control the tank with 2 tillers. One direct vision slit in the armor was provided, as well as a fully rotating periscope. For ease of driving during the night and visibility during maneuvers, the tank had a single headlamp on the right side of the upper hull. The radio operator was likely seated to the driver’s right, also in the hull. He also had a rotating periscope for vision.
The exact armament of the IS-M was never specified, other than its caliber, 122 mm. However, considering the German-style muzzle brake, it was a D-25T, as on the standard IS-2. The tank was equipped with 40 shells for the main gun.
122 mm D-25T ammunition specifications
Muzzle velocity (m/s)
3.6 kg TNT
42 mm (calculated)
Around the tank, 3 GVG 7.62 mm machine guns were mounted, one coaxial to the main gun, one in a ball-mount at the rear of the turret, and one in the frontal hull, which is not visible in the drawings. A ‘large caliber’ machine gun was to be added to the commander’s cupola for anti-aircraft purposes, likely a DhSK 12.7 mm machine gun, but it is not shown in the drawings either.
The SPG variant of the IS-M was likely armed with an 152.4 mm BL-8 gun, developed at the beginning of 1944 and tested during July of the same year on the ISU-152-1 (Object 246).
152 mm BL-8 ammunition specifications
Muzzle velocity (m/s)
5.86 kg TNT
The frontal plate was a continuous flat plate of 200 mm angled at around 45°. Side armor was 160 mm thick and angled at 60° on the upper hull and flat on the lower hull. The rear was also heavily angled and 120 mm thick. The turret was 160 mm all around, but being awkwardly rounded, it increased its effectiveness significantly frontally. This gave the IS-M superior protection to any heavy tank of the time, while still maintaining a modest 55 tonnes weight.
In the background of the original drawing, 2 additional vehicles can be seen. The first is also an IS-M, but with a different set of running gear, namely 6 IS-style road wheels and 3 smaller return rollers. This was likely added as an alternative to the large roadwheel design.
Further back, a completely different vehicle is shown, a form of SPG based on the IS-M. The turret was replaced with a fixed casemate with a large 152 mm BL-8 gun. Interestingly, the running gear is the same as on the previously described IS-M.
Return to Leningrad and Further Developments
The IS-M was short-lived. Alongside its 2 earlier counterparts, all were abandoned in April 1944. Instead, Factory No.100 began work on a vehicle meant to rival the SKB-2’s Object 701 and thus become the new generation heavy tank. It would incorporate several features from both the IS-M and the 2 wooden mock-ups presented on 18 April 1944. This was the IS-6, designed at first in secrecy. Like on the IS-M, 2 variants were designed, one with large diameter road wheels and a steeply armored hull (Object 252). The second would use an electromechanical transmission on an IS-2 lower hull (Object 253).
In May, with the Soviets having lifted the Siege of Leningrad, the SKB-2 design bureau and Factory No.100 were moved back, and thus the LKZ was revamped. Many engineers moved back, including Shashmurin. Back in Leningrad, they would continue work on the IS-6. In August 1944, the Object 244 was used as a testbed for the Object 252’s wheels, first designed on the IS-M, and later the 122 mm D-30 gun. The Object 244 itself was a prototype dating back to February 1944, meant to test the new 85 mm D-5T-85BM on an unmodified IS-1 (Object 237). The project was named IS-3, although this has nothing to do with the later IS-3 heavy tank (Object 703). After a military representative from Factory No.100 reported the IS-6 secret development to the GABTU, it was ordered that further development and prototype production should take place at Uralmashzavod in Yekaterinburg, but without the end game of entering production.
Back at ChKZ, which had been working full-time on the Object 701, it was realized that it needed to present its own modernization of the IS-2. Thus, in August 1944, they presented the blueprints of an upgrade to the IS-2. At first glance, it looked like an unchanged IS-2, but it featured various improvements, such as refined frontal armor layout, thicker turret armor, improved turret design, and many mechanical changes, such as improved cooling system and engine room. Allegedly, one prototype was built. Yet, by October 1944, the project was abandoned in favor of a new tank, which incorporated many IS-2 features, but was still radically new. It was called the Kirovets-1 and given the Object 703 index. After several alterations, most notably the addition of its most famous feature, the legendary pike-nose, the IS-3 was born.
The pike-nose on the IS-3 was ‘borrowed’ from the IS-2U and Object 252U, an upgrade of the IS-2 and Object 252 meant to equip them with pike-noses. As a matter of fact, the IS-2U, designed in November 1944, was the last genuine attempt to fundamentally upgrade the IS-2 heavy tank. The IS-2 U’s turret was itself heavily inspired by earlier designs, such as the IS-M.
The IS-6 would end up unsatisfactory. The GABTU never intended to adopt it into service regardless. The Object 253 with the electromechanical transmission caught fire during testing. Both IS-6s were deemed insufficiently armored in comparison to the IS-4, and once the IS-3 was nearing production, the fate of the IS-6 was sealed.
Shashmurin himself, who had worked throughout the entire development of the IS-6, was never fond of the idea. Just like on the KV-13, he was a true believer in what he called “tank of maximum parameters” a tank which pushed the capabilities of the industry and designers to their limit, in an attempt to reach an unstoppable heavy tank. His first such vehicle was the IS-1 and later IS-2. For him, the IS-6 was a waste of time, especially considering the end of the war. As for the rivaling ChKZ heavy tanks, he had the following to say:
After the war, Shashmurin would finally fulfill his dream of designing a true “tank of maximum parameters”, the IS-7, which indeed, pushed the technology of the time to its limits, being the heaviest Soviet tank ever built, as well as several work on ATGM-based heavy tanks, PT-76 and more.
The IS-M itself was a short-lived design meant to offer an arguably unnecessary upgrade to the IS-2. It would incorporate some very interesting features and solutions, such as a rear mounted turret, large diameter road wheels, and a curved hull. It alo took in consideration several running gear designs and an SPG layout. Nonetheless, despite its short life, it was a crucial factor in the developmental progress of Soviet heavy tanks during the Second World War, by leading directly into the development of the IS-6, which lost in turn to the more refined, though still crude, IS-3 and IS-4 designed at ChKZ. For Shashmurin, the IS-M was certainly not his most prideful creation, but through its odd nature, it complements well the career of one of the USSR’s most important heavy tank designers of the Second World War.
7 x 3.2 x 2.7 (m)/td>
Total Weight, Battle Ready
1,200 hp diesel (V12) M-40 with 4 turbochargers or 500-700 V series engines
The Panzerkampfwagen VI “Tiger” Ausführung E is one of the most outstanding and iconic vehicles in the history of tank building. The Tiger caused significant problems for the Allies when it first appeared at the front. Fortunately for the Allies, shortly after, several vehicles were captured by the Red Army and tested. In the Soviet Union, designers even worked on the option of re-equipping this German heavy tank with ‘domestic’ Soviet guns. However, this project appeared too late, and the imminent end of the war did not give this proposal any chance to materialize.
The Heavy Cat of the Wehrmacht
The Tiger I, or ‘Panzerkampfwagen Tiger Ausführung E’ (Pz.Kpfw.Tiger Ausf.E), was born in May 1942, but its conception and development can be traced directly back to 1936 and 1937, with work on a 30-33 tonne tank by the firm of Henschel und Sohn in Kassel. Just like other German tank projects, the development was very complex, overlapping with dozens of other projects, and has been the subject of a large number of books and movies. The name ‘Tiger’ itself has a no less complex history. It was first used in February 1942, when the project “Pz.Kpfw.VI (VK45.01/H) Ausf.H1 (Tiger)” was approved. The design was clearly identified as the Pz.Kpfw.VI or Tiger, with “Tiger I” first used on 15th October 1942, followed by “Pz.Kpfw.VI H Ausf.H1 (Tiger H1)” on 1st December 1942 and then “Panzerkampfwagen Tiger Ausf.E” in March 1943.
The Tiger I had a crew of five: commander (back left), gunner (front left), and loader (right) in the turret, and the driver and radio operator in the front left and right of the hull, respectively.
The main armament consisted of the 8.8 cm Kw.K. 36 L/56 gun in the turret. This gun was derived from the 8.8 cm Flak 18 and Flak 36 AA guns and delivered similar ballistic performance. It was combined with the excellent T.Z.F.9b 2.5 x magnification binocular telescope for the gunner. This T.Z.F.9b binocular sight was later replaced by the cheaper but no less effective T.Z.F.9c monocular sight, a change identifiable by the switch to a single hole in the left side of the mantlet. The Tiger carried 92 rounds of Armor-Piercing (AP) and High Explosive (HE) ammunition. Where available, the Pz.Gr.40 (high velocity, sub-caliber, tungsten core, with no explosive filler) round was also carried for use against heavy enemy armor.
Secondary armament consisted of a 7.92 mm MG.34 machine gun mounted coaxially with the main gun. This weapon had a maximum elevation of -8º to +15º. A second machine gun, a ball-mounted MG.34, was located in the right-hand side of the driver’s plate. This second machine gun was capable of 15º traverse to either side (total arc of 30º) and an elevation of -7º to +20º. It was fitted with a K.Z.F.2 episcopic sighting telescope with a magnification of x1.75. For these machine guns, 4,500 rounds of ammunition were carried. Another M.G.34 anti-aircraft machine gun (Flieger-M.G.) could also be carried on the turret (also fitted to the Befehlswagen-Tiger).
After June 1942, six 95 mm diameter smoke grenade launchers (in two sets of three) were approved for mounting on the turret, a process which started in August 1942. The launchers could fire the Nb.K.39 90 mm smoke generator grenades but, following combat reports of gunfire setting them off and blinding the crews, these were dropped in June 1943.
The Tiger was powered in the early production runs by the HL 210 TRM P45 21-liter V-12 Maybach petrol engine producing 650 hp at 3,000 rpm. Due to problems with the reliability of this engine, the maximum performance could not be achieved, restricting mobility for this heavy tank. As a result of the poor performance, the more powerful HL 230 TRM P45 23 liter V-12 Maybach engine producing 700 hp was introduced in its place from May 1943 onwards.
The Tiger’s suspension consisted of 55 mm diameter torsion bars (Stabfedern), which ran the complete width of the tank’s hull, with splined heads, although the two front and rearmost two bars were wider than the rest, at 58 mm diameter. The bars were connected to the road wheel arms (Laufrad-Kurbel), each of which had three road wheels. Their arrangement overlapped wheels from adjacent road wheel-arms, creating an interleaved pattern to spread the load of the tank onto the track. Hydraulic shock absorbers were fitted to the inside of the front and rear road-wheel arms which, combined with the damping effect of the torsion bar, created a very smooth ride.
On 29th August 1942, the first batch of Tigers from the 502nd Heavy Tank Battalion, consisting of four Pz.Kpfw. VI, advanced to combat positions from the railway station Mga, near Leningrad. Three vehicles suffered serious breakdowns leaving the station, and, in general, were not so successful. Later, during the battles to break the blockade of Leningrad, on 16th January 1943, Soviet troops captured a Tiger which was previously hit by artillery. This was followed by a practically intact one on 17th January. The crew left it without destroying even a brand-new technical passport, different tools, and weapons. Both tanks were evacuated from the combat area and sent to the Kubinka Proving Ground for studies.
Studying the «Wild Beast»
Initially, the captured tanks appeared in the correspondence as “captured tanks of the HENSHEL type”, later called T-VI. The tanks that arrived aroused great interest among the Soviet military command. By that time, the “Tigers” were actively used by the Germans both on the Soviet-German front and in North Africa. These vehicles were used for the first time on a truly massive scale during the battle for Kharkov, making a significant contribution to the defeat of the Red Army on this sector of the war front. Around the same time, the Tigers fought in Tunisia against American, British and Commonwealth troops, inflicting serious losses on them.
By April 1943, the two tanks, with turret numbers 100 and 121, were already at the proving ground. It was decided to test ‘121’ for armor durability and use ‘100’ for testing the gun against the armor of Soviet tanks.
The armor on the side of the Tiger’s hull managed to withstand the Soviet 45 mm guns. However, 57 mm guns of the ZiS-2 type overcame the 80 mm side armor with ease even from a long distance (up to 1 km). The frontal armor of the tank could not be penetrated by the 76 mm F-34 gun, the main Soviet tank gun at that time. The 85 mm “anti-aircraft gun” 52-K performed much better in this regard, penetrating the “Tiger” in the front from a distance of 1 km. The 122 mm A-19 gun performed the best at this. Until that moment, it had not yet been considered as a possible tank cannon. After two hits fired from it, the once formidable German heavy tank turned into a pile of scrap metal.
The tests of the German 88 mm tank gun were much more impressive. It was used to fire at Soviet T-34 and KV tanks. The main Soviet heavy tank of that time was easily penetrated from a distance of 1.5 km. Even the uparmored version with additional protection was also penetrated. For the T-34, the very first shot, from a distance of 1.5 km, “decapitated” the tank. Its turret was “knocked off” the hull, while significant damage to the frontal part of the hull was caused by further shelling. It is worth noting that the aforementioned Soviet anti-aircraft gun 52-K showed similar results in tests.
Tests of the new German heavy tanks showed the Soviet military command the need to gradually abandon 76 mm tank guns in favor of larger calibers, such as 85 mm and 122 mm. At around the same time, accelerated work began on self-propelled guns, such as the SU-85 and SU-152, as well as on the KV-85 and IS-1 heavy tanks.
A Stranger Amongst Us
The sporadic capture of workable versions of the Tiger tank by the Red Army was the main reason for the episodic nature of its combat use on the side of the USSR. In addition, Soviet tankers, in an effort to get a high reward, almost always destroyed the rare Pz.Kpfw. VI.
The first reliable case of the use of a captured “Tiger” in battle was recorded only at the very end of 1943, with the crew under the command of Lieutenant N.I. Revyakin from the 28th Guards Tank Brigade. On 27th December 1943, one of the “Tigers” of the 501st Tank Battalion got stuck in a crater, its crew ran away, and the tank itself was captured. On the next day, the tank was assigned to the 28th Brigade. Revyakin was appointed commander of the captured heavy tank because he already had extensive combat experience and military awards, two Orders of the Patriotic War of the 1st degree and the Order of the Red Star. On January 5th, the captured tank, with red stars painted on the sides of the turret and with the writing “Tiger” added as well, went into battle.
The operational service of this vehicle with Soviet units looked quite typical for German heavy tanks. It almost always required repairs. The matter was greatly complicated by the lack of spare parts. But this was on the battlefield. In the bowels of the Soviet design bureaus, there had been several projects developed to re-equip captured German vehicles with Soviet guns since 1942. Similar proposals were made for the Tiger, but they started much later, at the end of 1944 and the beginning of 1945.
T-VI-100: Unrealized “Frankenstank”
On 28th November 1944, the Artillery Committee at the Main Artillery Directorate of the Ministry of Defense of the USSR (AK GAU) issued tactical and technical requirements No. 2820 “For the installation of domestic weapons in the turrets of captured German tanks T-IV, T-V, T-VI and the Royal Tiger” (due to the lack of a full-scale model of the Pz.Kpfw. VIB Tiger II turret, the study of the change of armament of this tank with a domestic gun was not carried out), including the adaptation of these turrets as stationary firing structures. Simply put, OKB-43 needed to take the turrets from captured tanks, replace the German guns with Soviet ones, along with sights, and further adapt them for installation on armored vehicles.
In January 1945, GSOKB (рус. Государственное Союзное Особое Конструкторское бюро – State Union Special Design Bureau) No. 43 at the NKV (рус. Народный Комиссариат Вооружения СССР – Ministry of Armaments of the USSR) presented a project for installing the latest 100 mm D-10T tank gun, which in the future would become the main armament of the T-54 medium tank, with the Soviet TSh-17 sight, in the turret of the T-VI tank (how trophy “Tigers” were designated in the USSR) while retaining its gun mantlet. This conversion process was estimated at 90 hours of work. The conversion provided for the installation of a shell casing removal system, which simplified the work of the turret crew.
At the end of 1943, on an initiative basis and in the shortest possible time, the team of designers of Design Bureau of Plant No. 9, headed by F.F. Petrov, developed a 100 mm gun system designed for installation in the SU-100 tank destroyer. The cannon, the lead designer of which was M.E. Bezusov, received the designation D-10. The barrel length was 56 calibers (5,610 mm), and the initial velocity of the projectile was 900 m/s. The rollback length of the D-10S turned out to be longer than that of its competitors and was about 510-560 mm. Structurally, the gun system was a logical successor of the Design Bureau of Plant No. 9’s earlier projects, and when it was created, maximum unification with them was achieved. For example, cradle, lifting and turning mechanisms were taken from the D-25T 122 mm gun.
The history of the 100 mm D-10 gun did not end with the SU-100 tank destroyer. It would also appear on such Soviet late-war prototypes as the T-34-100 and SU-101 (a.k.a. Uralmash-1). After the war, it would be modified many times (hence versions like D-10T, D-10T2, M-63, D-33, 2A48, etc.) and become the main gun of the Soviet medium tanks of that period, the T-54 and T-55. It would also be proposed for some Cold War Soviet tank destroyers, such as the SU-100P and the Obj. 416, for Chinese medium tank Type 59 (WZ-120), and for light amphibious tanks prototypes, such as the Obj. 685 and the Obj. 934.
Project Description. Comparison with Tiger I Ausf. E
The Soviet military command liked the proposal of the installation of the Soviet D-10 gun, which had proven itself on SU-100 self-propelled guns, in the turret of the German Tiger tank. Indeed, the 88 mm KwK 36 tank gun, so formidable in the early stages of the war, was no longer that impressive by 1945. This was understood by the Germans themselves, who managed to design a lot of self-propelled guns armed with a 128 mm KwK 44 gun, and one of them, the JagdTiger, was even built and used in battle.
8,8 cm KwK 36
168 g charge
(285.6 g TNT eq.)
64 g charge
(108.8 g TNT eq.)
0.646 kg charge
(1.1 kg TNT eq.)
689 g TNT
146 mm pen
165 mm pen
210 mm pen
110 mm pen
Parameters of penetration are given for 0 m and 0°.
Original T-VI gun… (source — ZA DB, Pablo Escobar’s gun table)
100 mm D-10T
65 g charge
(100.1 g TNT eq.)
1.46 kg TNT
210 mm pen
215 mm pen
Parameters of penetration are given for 0 m and 0°.
… and a Soviet “replacement” for the T-VI-100 proposal (source — ZA DB, Pablo Escobar’s gun table)
The Soviet gun significantly surpassed the KwK 36 in terms of firepower. With comparable accuracy, it had higher penetration, muzzle velocity, and much more powerful HE shells. With all the ‘pluses’, it was only slightly inferior to the German gun in terms of rate of fire.
The larger caliber affected two technical characteristics of the vehicle, the elevation arc and the amount of ammunition. According to the author’s estimates, instead of 92 shells of 88 mm caliber in the German original, the T-VI-100 could carry only about 50 shells of 100 mm caliber. The dimensions of the breech and the shape of the barrel influenced the downward elevation arc of the gun: instead of -8° in the frontal part and -3° in the rear in the Tiger I Ausf. E, the maximum depression became -4° all around. The upward elevation arc of the gun remained the same at +15°.
Inside the turret, space became much tighter. The breech of the new gun would now occupy ~75% of the turret length instead of 50% previously.
The cannon was not the only German component replaced with a domestic one in the proposal, with the coaxial machine gun as well as the sight being changed. The German 7.92 mm MG-34 was substituted with the Soviet 7.62 mm DT with a disk magazine, while the German TFZ-9 sight was replaced by the Soviet TSh-17. In the future, the same sight would be used on IS-2 and IS-3 Soviet tanks. It can be assumed that the machine gun in the hull would also have been replaced by a DT. Although there is no documentary substantiation of this hypothesis, such a decision would have been logical.
However, many other problems remained unresolved. There was no talk of replacing the transmission, engine, and other hull components with Soviet ones, which means that repairing them would have been problematic. Obviously, if the T-VI-100 was built in metal, in field use, all the ‘charms’ of exploiting captured German vehicles by the Red Army would have been preserved to the great displeasure of the crews and mechanics.
The Fate and Prospects of the Project
In general, the project was judged positively and was approved by the High Command, but things did not move beyond the project documentation. By spring 1945, the need for such projects had disappeared due to the proximity of the end of the war in Europe.
The Tiger I itself was outdated by 1945. Its armor could no longer ‘surprise’ anyone. All this indicates that the T-VI-100, if built, could not fulfill the previous role of “heavy tank for breakthroughs”, which was performed by the Tiger I in the first years after its appearance at the front.
It seems, however, that there was another possible option for using the developments on the project, selling a “modified” version to third countries. However, the logic behind this seems flawed, as most of these, especially those that never operated such a heavy tank before, the “Tiger”, even with a 100 mm gun, would probably not have been needed (and Germany itself was already not allowed to have its own army). For the emerging Soviet-bloc countries, such as Czechoslovakia, Hungary or Poland, especially ones bordering what would in the future become NATO, the T-VI-100 might have been a good temporary stopgap for their weakened armies until Soviet supplies of T-34-85s, IS-2s, T-54s, etc. would have become the norm. It is important to keep in mind that plans including Operation Unthinkable, a British invasion of East Germany, were actively developed, and tremendously dangerous for the weakened and war-torn USSR and its satellites at that time. Moreover, the first frontier of the possible Third World War would surely have been in Eastern Europe. On the other hand, it is doubtful that rearming a quite rare and outdated captured tank type was easier and more useful for the aforementioned countries rather than waiting for the mass-produced T-34 or IS-2.
The project of the T-VI-100 tank, like many of its analogs, belongs to the category of “the war ended too soon”. On the one hand, although this was a fairly reasonable alternative to the simple disposal of captured vehicles, serious improvements were still required for its full-fledged and practical implementation, especially to the hull. On the other hand, for one of the tasks of the project (the aforementioned possibility of using turrets with a new gun system as stationary firing points), the existing level of development was more than enough. But such defensive systems would have also hardly been needed by the Soviet Union after 1945.
Instead of an Afterword: T-VIB-100
As mentioned above, captured King Tigers were also considered for rearming with domestic (Soviet) weapons, but these proposals were not worked on due to the lack of turrets and data on them.
Still, it can be speculated what exactly may have been included in the hypothetical ‘domestication’ of the “Tiger-B” (or “T-VIB”), as it was called in the USSR. TZF-9 sights, just like on T-VI-100, would likely have been replaced by the TSh-17. The 7.62 mm DT machine gun would have likely taken the place of the MG 34.
A more difficult question is which Soviet weapon could have replaced the German 8.8 cm KwK 43. The choice would probably have been between the 100 mm D-10 and the 122 mm D-25 tank guns (there is no sense in replacing KwK 43 with less powerful guns of smaller caliber). Since the second variant, due to its large caliber, would require a large amount of space (for the breech, counter-recoil mechanism, and ammunition), the D-10 seems to have been the most optimal alternative to the German gun.
The vehicle itself would probably have been named similarly to the T-VI-100: T-VIB-100, but “Tiger-B 100” variant is also possible. However, all this is just a hypothetical conception and speculative thought of “what-could-have-been”, and was never actually developed.
Special thanks from the author to his colleagues Andrej Sinyukovich, Pavel “Carpaticus” Alexe and Pablo Escobar.
T-VI-100 specifications table
8.45 x 3.547 x 3 m
Total weight, battle ready
5 (commander, gunner, loader, driver, and radio operator)
Maybach HL 210 P.30 petrol engine (650 hp) or
Maybach HL 230 P.45 petrol engine (700 hp)
45 km/h (road max.), 30 km/h (road sustained) or
40 km/h, 20-25 km/h (firm ground sustained)
348 liters, sufficient for a range of up to 120 km road, 85 km firm ground. Two spare 200-liter fuel drums could be carried on the back deck for long road marches.
100 mm D-10T
2x 7.62 mm DT
~50 rounds 100 mm,
~4,500 7.62 mm ammunition
Driver’s plate – 100 mm @ 9º
Nose – 100 mm @ 25º
Glacis 60 mm glacis @ 80º
Hull Sides Upper – 80 mm @ 0º
Hull Sides Lower – 60 mm @ 0º
Rear – 80 mm @ 9º
Roof and Belly – 25 mm
Mantlet – 120 mm @ 0º
Front – 100 mm @ 5º
Sides and Rear – 80 mm @ 0º
Soviet Union/German Reich (1932)
Superheavy Tank – None Built
In armored terms, few tanks evoke more awe in terms of size and specifications than the Maus, a 200-tonne behemoth from the tank-stable of the even more famous Dr. Porsche. It is also no secret that there is a certain following, especially online and in the media generally, for what could, at best, be described as ‘Nazi Wonder Weapons’. It is not that any one of these ideas could have won the war for Germany, that was simply not going to happen in 1945 regardless of whatever vehicle, missile, or plane the Germans developed. What they were, however, is a reflection of the giant level of engineering and imagineering which ran amock at times in Nazi Germany. A political mindset wanting a 1,000 year Reich was also thinking huge in every conceivable area, from giant planes to super-ships, rockets, and, of course, tanks. If the Maus impressed as a 200-tonne vehicle, then imagine a vehicle 5-times that weight; a true goliath.
Online, that vehicle has become known as the ‘Ratte’ (Eng: Rat), as some kind of allusion to its Maus-sized forebear, but the vehicle was less rat-sized and more landship-sized and was known under the less amusing name of ‘P.1000’. Perhaps even more surprising than its incredible weight and size was that this vehicle was not some late-war attempt to wrestle victory from defeat by overwhelming Allied superiority, but began life in the 1930s. More than that, it did not even begin life in Germany, but in the nation to become Nazi Germany’s greatest enemy, the Soviet Union.
The Men Behind the Tank
The primary figure in the story of the P.1000 is the enigmatic Edward F. Grote. (Note that his name is repeated numerous times online and in books as ‘Grotte’, but is very clearly written as Grote with one ‘t’ in both British and German patents, so his name assuredly was ‘Grote’). Grote’s work on huge tanks had begun early during the time he spent working in the Soviet Union (USSR). A skilled engineer, Grote had lived in Leipzig between 1920 and 1922, running an engineering concern where he had received several patents for engines, in particular diesel engine innovations. These included methods of cooling and also lubricating those engines with oil under pressure. Grote’s interest in power transfer and diesel engines would be very useful when it came to designing large and heavy tanks.
The Soviets had, after April 1929, tried to emulate the French FCM Char 2C with a project of their own. They had tried to engage foreign engineers and designers and were interested in the ideas of Edward Grote. Grote’s skills led him, by 1931, to become head of the Soviet design team for this new giant tank, his firm having been selected over two rival firms in 1930, primarily for political reasons – Grote was a sympathizer of the Soviet government and one of his engineers was a member of the German Communist Party. His task for the Soviets was to develop a breakthrough tank able to match the French FCM Char 2C and the order for this work was dated 5th April 1930. At the time, the specifications for this breakthrough vehicle were perhaps somewhat unremarkable, with a weight of just 40 tonnes and armor not less than 20 mm thick.
A design bureau known as AWO-5 was set up in Leningrad (now St. Petersburg) for him to conduct this work. By 22nd April 1930, just over two weeks since the task was officially set, the preliminary outline was ready. This design became the first in a series of ‘TG’ tanks – TG for ‘Tank Grote’.
The Soviet TG or TG-1 tank was designed with the involvement of Edward Grote.
In just over a year, the first prototype was ready for trials, but the novel track design was a particularly weak point of the design. Added to this was that the cost was excessive, to the extent that the BT-5, an 11.5-tonne tank with an armor of just 23 mm at best, was preferred instead – hardly suitable for a breakthrough role, although its speed would be useful for exploitation of a breakthrough.
More versions of the TG followed and it inevitably grew larger, heavier and more complex in doing so, with the sixth and final version presented in May 1932. By this time, the Soviets had seemingly grown weary of a project which was producing increasingly large and expensive tanks when there were alternatives available, such as emulating the British A1E1 Independent.
The result was that the Soviets turned from this German design to their own vehicle inspired by the British A1E1 and which was ready in 1933, in the form of the T-35A. At over 45 tonnes, this tank was large – nearly 10 m long, and was fitted with 5 turrets, although armor was just 30 mm at best.
The First Fortress Tank
Grote, however, had not given up on his increasingly large tank ideas. It is worth noting that the big size limiter for tanks is based around the size and weight which can be borne by roads, and especially railways. These limitations restrict the maximum width and height of the vehicle more than the length. This has historically resulted in some very long vehicles, as the designers of the vehicles struggle to provide the armor and automotive power within these strict limits.
Grote, and several designers before and since, have understood that, as soon as you step beyond these maximums, there is no point in a vehicle a little wider or a bit taller than could be carried by train. Indeed, the decision to go big from a design point of view is technically very freeing, as the dimensions can be made whatever they need to be to fulfill the role of the vehicle. If, like it was for Grote, the need was for a well-protected breakthrough tank with a lot of firepower, then freeing himself from those strict limits meant he could make a big tank to mount big guns. It would need a big engine or engines to power it but, again, there was effectively no limit on the volume into which the unit or units required to power the vehicle could fit.
Liberated from the width and height restrictions of the rail gauge, Grote had gone beyond the plausibility of his TG vehicles and, in March 1933, submitted a new, massive, and less plausible vehicle concept to Soviet Marshal Mikhail Tukhachevsky. Tukhachevsky was a key figure in Soviet military modernization in the 1930s before he, like millions of others, fell victim to the murderous purges of Joseph Stalin. The dimensions of the vehicle were truly staggering. A hull 34 meters long, 10 meters wide, and 11 meters high, it was topped with a pair of 305 mm guns in fully rotating turrets. A pair of smaller turrets, each fitted with a pair of 152 mm guns, were mounted on the front corners of the hull, and two more turrets, each fitted with a pair of 76 mm guns, were fitted aft of the primary turrets. If that was not enough firepower, two further turrets, each fitted with a 45 mm gun, were also to be mounted.
The sides of the hull were vertical and used heavy armor plating 250 mm thick to cover the enormous road wheels* and suspension. The front of the tank was very well angled and was to be 300 mm thick. This 300 mm of armor was to be repeated on the front of the primary turrets and roof armor was to be 100 mm thick. Certainly, this would have been sorely needed given the size of the tank and what a target it would have made for enemy artillery or aircraft. The thinnest part of the armor was the hull floor, at 60 mm thick.
Supported on a trio of 1 m wide tracks on each side, there would be 6 m of track width on the ground. Given that the vehicle was estimated to weigh 1,000 tonnes, this track, with a ground contact length of 20 m, spread the great load and the ground pressure was calculated to be just 0.72 kg/cm2 (about half that of the 180 tonnes Pz.Kpfw. Maus), a little more than that exerted by a heavily laden man’s foot. This was truly the Festungs panzer or ‘Fortress’ type tank Grote was picturing, with a crew of not less than 40 men to command, drive, maintain and operate all of the weapons, but it was also no slouch despite its huge mass.
(* assuming the 1942 rebirth was just a revamped version of his 1933 idea, then the wheels would be around 2.5 m in diameter)
By virtue of twelve 2,000 hp 16-cylinder diesel engines (24,000 hp / 17,630 kW total) and a special hydraulic transmission, Grote expected his 1,000 tonne monster to manage up to 60 km/h. One of the crucial advantages the enormous size would give Grote would be the obstacle-crossing ability of the tank. With its high leading edge of track, his tank would be able to climb a vertical step no less than 4.8 m high and ford an 8 m deep river without having to concern itself with bridges.
With the design submitted, it was reviewed and found to have serious problems. Not the least of these was that the planned engine power and speed of the vehicle were not realistic. There was simply no engine producing 2,000 hp available. The V-16 (cylinders at a 50-degree angle) 88.51 liter Mercedes-Benz MB502 marine diesel engines, could, at best, produce just 1,320 hp at 1,650 rpm or a continuous output of 900 hp at 1,500 rpm. Assuming 12 of those could be used, then this would produce a continuous 10,800 hp or a maximum of 15,840 hp, well short of the 24,000 hp needed. The engines were to have been laid out 6 on each side and all driving a common driveshaft. This power was then to be transmitted either hydraulically or electrically to the drive sprocket.
A supercharged version of that engine was also available later, but this was not in production when Grote’s design was submitted. That engine, the MB-512, could produce the same continuous 900 hp as the MB-502 at 1,500 rpm, but an improved 1,600 hp maximum output at 1,650 rpm. Even if this improved version was available to Grote, it would, at best, have delivered just 19,200 hp combined maximum – just 80% of what he needed.
With no suitable engine available, the Soviets could not accept Grote’s design and would soon part company with Grote and embark on their own fortress-tank work. With the failure of the TG tanks and now this fortress tank, Grote’s work in the Soviet Union came to an end and he returned to Germany in 1933.
Back to Germany
Grote, now living in Berlin, did not stop his engineering and submitted another patent application in 1935. Several more patents followed, relating to transmissions and hydraulic couplings but also, and more importantly, for tracks as well.
In January 1935, Grote filed a patent application for a novel type of caterpillar track. In his design, half of the metal links of a common style of track were to be replaced by intermediate links made of rubber sandwiched between the steel links. These rubber links would be in compression all the time, squashed between moving metal links on each side. The design would serve not only to create a lighter type of track but also one completely under tension the whole time, which would improve the efficiency of the driving force applied to the track. Perhaps more unusually, none of the links were actually physically connected together in the sense of a track pin. Instead, each track consisted of a pair of flexible chains, rather like the chain on a bicycle or chain saw, which would loop around the drive and road wheels. Each metal link would have two hollow channels made in it for each of these chains to pass through, and then, between each metal link, two of these smaller rubber intermediate links were placed, each with a single channel for the drive chain to pass through. The rectangular shape of the chain and of the channel in both the rubber intermediate links, and the metal links also prevented twisting of the links, or, in the case of the rubber links, any rotation from taking place. As the entire system was in compression the whole time, it also served to provide a completely sealed track system for the chain, so as to keep out dust, which would otherwise increase the wear and tear and reduce the track’s service life. Unlike a continuous rubber belt type track system, where damage means having to replace the whole length of track, this idea meant that localized repair was possible.
Another of his patents, submitted in 1936, was for a moveable caterpillar track system. In that invention, the leading edge of the track could be changed so as to be low during road movement or raised to climb obstacles. There is no mention of tank design in either the metal-rubber-metal track design patent or in the elevated track patent, so it might be assumed that there was no military element involved in his designs.
Arguments with Burstyn
With some tank-related patents behind him, Grote saw himself referenced indirectly in a December 1936 magazine article that had stated that a German engineer had designed a 1,000-tonne tank for the Soviets. Grote chose to write his own piece in response defending the size of the vehicle he had designed and this appeared in the Kraftfahrkampftruppe magazine in 1937.
In doing so, Grote had managed to earn the ire of Günther Burstyn, the same Günther Burstyn who designed a tracked vehicle in 1912 and had tried, unsuccessfully, to get interest from the Austro-Hungarian Empire in the idea. Burstyn was scathing in his own views on Grote’s concept, saying it was not only impractical due to its size, but also had no military utility, perhaps forgetting how naïve and impractical his own idea had been.
Burstyn’s primary complaint was the weight of the vehicle based on the false assumption that more mass meant it would be immobile. The ground pressure for such a massive machine was not particularly great, as it was to have 6 sets of tracks, with each putting around 20 meters of track on the ground. With each track 1 meter wide, 6 of them, with 20 meters of length meant a track contact area of 120 m2 (20 m x 6.0 m) and producing a ground pressure of 0.72 kg/cm2, very low for a vehicle of its dimensions. For reference, the German Pz.Kpfw. VI Tiger produced around 1.04 kg/cm2
Further to this, Burstyn was also critical of the top speed. The desired top speed of 60 km/h was not possible with the engines available at the time but Burstyn did not claim it was impractical for that reason, instead, it appears to be based on the notion that big equals slow. Certainly, 60 km/h was not going to be possible even under the best of situations, as the engines required were lacking, but even assuming he could manage half of the required engine power, it is fair to assume Grote’s design would at least have matched the comparatively slug-like 15 km/h top speed of the French FCM Char 2C. Further, the role such a gigantic vehicle would have to perform in smashing enemy lines, positions, and formations, and high speeds would not be needed anyway. It could not go so fast as to outstrip accompanying and supporting vehicles and troops anyway.
Unlike the FCM Char 2C, Grote’s Fortress tank concept would not use multiple small road wheels but would, instead, use several (the exact number varies in the artist’s impressions) very large diameter (~2 – 3 m) double road wheels per track section. Each of these sets of wheels was mounted into a bogie and that bogie was sprung by means of hydraulic cylinders with a compensator of some type. Steering would be produced by simply braking one side of the tank.
On the matter of immobility, Burstyn was simply incorrect and working on an incorrect premise. He was not, however, wrong in his critique of the military utility of the vehicle, but Grote would have a long way to go before he could prove or promote his ideas again.
The 1933 concept was the culmination of tank work in the Soviet Union, where the tank had got bigger and bigger to accommodate more and more armor and firepower and the larger and larger engines needed to propel the machine. Trying to achieve the goals of heavy armor impervious to enemy fire, heavy armament, and high mobility seem impossible at first glance, especially given the inherent constraints on the size of a vehicle. As Grote would find, the only way to achieve everything he wanted was to step out of the physical limits imposed by things outside of tank design, such as road widths, bridging, and rail gauges. Once those limits were exceeded even slightly, there was suddenly no real limit on the size of the machine and he could start with huge amounts of firepower and massive sections of armor. In doing so, he also would need a means of propulsion which was not available to him at the time. The ‘1,000 tonnes’ was probably as a symbolic weight that might grab the attention or funding which an ‘872 tonne’ design might not, but Grote had embarked on a slippery slope with no limits imposed. The end result was a gargantuan machine which, whether or not it would even move, was irrelevant to what practical use it could possibly have had.
Untethered from the reality, limits on size the machine had grown perhaps way beyond what he had wanted, to a vehicle of huge proportions with a ludicrous array of armament. Grote’s design, quite rightly, was rejected by the Soviets, for whom a simpler and more conventional machine, well armored and armed, would find favor well after the T-35A.
It is perhaps ironic that the lessons learned by the Soviets from this German flight of fancy had to be relearned by the Germans a few years later. Grote, in fact, went on to further refine his ideas. During that development, the dimensions were still gargantuan for a tracked armored fighting vehicle, but the design did at least get a little less ridiculous as it went on, at least in terms of fewer turrets. The weight and armament of those designs, however, remained excessively large and they were equally unsuccessful.
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Grote’s 1,000 tonne ‘Festungs Panzer’ concept, March 1933 specifications
34 m Long x 10 m Wide x 11 m High
Total weight, battle ready
12 x 2,000 hp
60 km/h desired
1 x twin 305 mm, 2 x twin 152 mm, 2 x twin 76 mm, 2 x 45 mm
300 mm front, 250 mm sides, 100 mm roof, 60 mm floor
The IS-7 (Object 260) is one of the most well-known tanks developed by the USSR, in part due to its massive size and weight, placing it with the likes of Tiger II. However, few know about its lengthy and intricate development process, consisting of many years of work and prototypes, with a total of seven different prototypes sharing the name IS-7. One of these was the Object 257, the bridging in between the failed IS-6 and the renowned IS-7.
In February of 1945, a replacement program for the Object 701 (IS-4), which had just started development seven months earlier, was requested by the GABTU (Main Directorate of Armored Forces). The SKB-2 factory, which designed the Object 701, was too busy with it and was working on its production. This left a window of opportunity for Factory No.100 to take over and begin work on the IS-4 replacement. Factory No.100 had just lost to SKB-2, as the Object 252 and 253 (IS-6) were deemed inferior in many ways to the Object 701. An upgrade to the Object 252, known as the Object 252U, was made in November of 1944, using pike-shaped angled armor with help of engineers from NII-48 research institute. However, the changes were not able to revive the already canceled IS-6. Despite its failure, it served as a good basis for the upcoming heavy tank.
On 7th April 1945, requirements for a 122 mm tank gun with a muzzle velocity of 1,000 m/s (3,280 fps), two-part ammunition, and a rate of fire of four rounds per minute (15 seconds reload) were issued. Factory No.100 had already done work with OKB-172 on the BL-13 gun which was used on the late alterations of the Object 252 and 252U. Earlier prototypes of the IS-6 had the D-30. This new gun was called BL-13-1 and featured improvements over the BL-13, such as a mechanical gun rammer, increasing its rate of fire to a whopping 8-10 rpm. Even a mechanical autoloader was tested, but, despite its claimed solid reliability, it was sluggish and was not worth losing a crew member on. It also decreased the rate of fire to 7-8 rounds per minute at a higher price tag. Nonetheless, the idea was never fully dropped, as the final IS-7 prototype used a loading assistant, using a conveyor belt. The shells were however larger, as the gun had a 130 mm caliber.
Work started on the new heavy tank in May 1945 with P. P. Isakov, who had previously worked on the Object 252U and IS-2U projects, as chief designer. The turret was taken directly from the Object 252U, and so was the pike-nose design. The engine and transmission, rather interestingly, were taken from the Object 253, the IS-6 variant which used a mechanical-electrical transmission, which caught fire during trials, was expensive and unreliable. The biggest change was made to the lower hull and suspension. This project would get the designation Object 257 and was the first design to get the name IS-7.
As mentioned earlier, many elements from the IS-6 program were used in Object 257. The turret and pike nose came from the Object 252U and the engine and transmission from the Object 253. However, one of the main focuses of the Object 257 project was sturdier protection. The same principle applied on the pike nose, which was implemented on the side of the hull as well. The previously flat hull sides were now angled inwards at an extreme angle, forming a diamond shape silhouette from the front and rear. On the downside, this caused huge internal problems. Primarily, torsion bars could no longer be used, since the hull was too narrow, meaning that the suspension had to be moved on the outside of the hull. For the suspension, four volute springs were mounted on each bogie, with two wheels per bogie, a very similar design to that of the American M4 Sherman. This made the Object 257 one of the most unique looking Soviet heavy tanks of the post-war era, as this was the first time a Soviet tank used volute spring suspensions.
The turret was identical to that of the Object 252U, being heptagonal and of a low profile. Inside, the gunner was seated to the left of the gun, with the commander behind him. The loader was located to the right of the gun. A coaxial machine gun was also mounted to the right of the gun, and could be fired by the gunner. It is unclear if it was a 7.62 mm SGMT machine gun or a 12.7 mm DShk heavy machine gun. The loader was responsible for loading this weapon as well.
As the Object 257 focused mainly on protection, crew comfort and overall ergonomics of the tank had to be sacrificed. The pike-like front end of the vehicle decreased the amount of space available for the driver. As shown in the drawing, the driver’s pedals would be located high up, his feet being on the same level as his torso. This would have been uncomfortable, especially when driving for longer periods of time. The driver had an entry and exit hatch on top of him, however, it was directly under the gun, meaning that entering and exiting would have been frustrating when the barrel was over the hatch. To add to his misery, he only had one periscope, relying more on the commander for command.
The gunner and commander could sit on chairs mounted to the floor through a long arm. Even for them, the conditions were not great. The low turret profile gave them very little headroom, not to mention it restricted the main gun from depressing more than a few degrees. The commander’s position lacked a cupola, and only had one periscope facing forwards and one backward. This further limited his visibility.
The loader was to the right of the gun, having to push the shells in with his left arm, a rather large inconvenience, considering the size and weight of a 122 mm shell. In addition, the ammunition was made out of two parts, the shell and the cartridge. In a turret bustle at the back, 30 rounds were stored, protected by an armored case. The cartridges were stored along the sides of the hull, diagonally, meaning that if one cartridge was taken out, another could possibly slide down. This, however, is only speculation. The average loader could load the gun in around 15 seconds. More warheads were stored in the hull, behind the driver. All this meant that the loader could easily load in the warheads, but had to bend down to grab a cartridge. As indicated earlier, an autoloader system was designed, however, despite its reliability, it was slow. If an autoloader was used, it is unknown if the loader would have been dropped or he would have had other tasks.
One of the most interesting aspects of this tank is the armor layout. The pike nose was an increasingly common feature in Soviet heavy tanks of the time. It was 150 mm (6 inches) thick, angled at 28° from the side. Yet the lower hull was completely new. Instead of flat plates, like on the IS-6, the plates were angled inwards, forming the same effect as a pike nose. This would have helped immensely against incoming rounds, deflecting them into the ground. The top parts were 150 mm (6 inches) thick and angled at 30°. The bottom plates were 85 mm (3.3 inches) thick angled at 23°. This thickness was not maintained all the way to the bottom of the hull. Halfway in, the armor was thinned down to only 20 mm (0.8 inches) yet kept at the same angle. This was most likely done to save weight, as the chances of enemy fire hitting this area were rather low, with the large suspensions being in front. The new side armor was impenetrable to the German 105 mm Flak 39 and the front was even strong enough that the BL-13-1 gun could not penetrate it at point-blank range. The turret armor was thick as well. The sides, although tinner in some areas, since they were curved, were 150 mm (6 inches) thick, angled at 45° degrees. Of course, this came at a cost. The weight of the hull increased to 23 tonnes (25.3 tonnes) over the IS-6’s 21 tonnes (23 tonnes).
If there is something that makes the Object 257 stand out, it is the suspension. As previously stated, the lack of room in the hull meant that the suspension had to be moved on the outside. Curiously, a bogie with four volute springs per wheel was used. These were very similar to the M4 Sherman medium tank, and it is entirely possible the design was derived from it. The wheels were mounted on opposite sides of the bogie and had arms on either side. These arms would then be attached to two volute springs that compressed when the wheel moved upwards.
As the weight had been increased up to 55 tonnes (60 US ton) on paper, a new engine was needed. Since 1944, Factory no.77 had been working on a new engine, based on the V-2, called V-16F. It was coupled to a similar (if not the same) electric transmission used on the Object 253. However, this engine was deemed very poor. Trials took place between March and May of 1945 and it was found to be unreliable. Even supercharging the engine to 600 or 750 hp that the IS-6 and IS-4 had would have put a huge strain on the engine, and failures occurred. Even at 520 hp, the engine was faulty. However, an engine this underpowered would have been disastrous if mounted on a 55 tonnes heavy tank, considering a 50 km/h (31 mph) speed was wanted. Further development was done on the V-16F, however, efforts were abandoned, and improved V-12 engines were used on the further IS-7 project.
New German heavies and Conclusion
After the discovery of the Maus and Jagdtiger and their analysis, the armor on the Object 257 was deemed insufficient. The 128 mm KwK 44 guns of the Jagdtiger and Maus would have pierced the hull. Likewise, the armor on the Maus and Jagdtiger was too strong for the BL-13. All this meant that the Object 257 needed to be reworked significantly. In addition, on 11th June 1945, the requirements of a new heavy tank were set by the GABTU. The weight increased to 60 tonnes (66 US tonnes) and the new armament was to be an S-26 130 mm gun. Lastly, torsion bar suspension was required. The Object 257 clearly was not adequate, leaving factory No.100 to start work on a new heavy tank. Nonetheless, work was not in vain, as the experience gained and armor features of the Object 257 were passed on. Many other tanks were designed, until the final Object 260 was made, the IS-7 we know today.
122 mm BL-13-1 2-part ammunition gun
co-axial 7.62 mm SGMT machine gun
Front top plate: 150 mm at 28°
Front bottom plate: 150 mm at 40°
Side top plate: 150 mm at 30°
Side bottom plate: 85 mm & 20 mm Turret armor
Front: 150 mm
Side: 150 – 120 mm
Rear: 100 mm
Top: 30 mm
In the later years of the Second World War (‘The Great Patriotic War’ to the Soviets), there was a quest to develop a replacement for the IS-2 heavy tank. The development process resulted in the IS-6 (Object 252/Object 253) and IS-4 (Object 701). This program was as secret as it was ambitious, with two rival factories working on their designs in absolute secrecy in fear of leaking information to one another.
On paper, the IS-6 seemed superior to any Panzer in Germany’s arsenal at the time. However, due to its mechanical issues and overall poor performance, it lost to its competitor, the IS-4, which would go on to enter service in 1946. Despite this, a last ditch effort to revamp the IS-6 was made, with limited success. This renewed vehicle would become known as the Object 252 November improvement – more commonly known as the Object 252U.
The Object 252 upgrade from November 1944 might have never gotten an official designation. Yet modern historians and video game company Wargaming have called it Object 252U, with the ‘U’ probably coming from the romanized Russian word ‘улучшенный’ (uluchshennyy). For simplicity’s sake, we will refer to it as Object 252U for the rest of the article.
After the battlefront experiences of 1943, with the appearance of the new German heavy tanks and tank destroyers such as the Ferdinand, the Soviet Union quickly realised that a new heavy tank was needed. Thus, in November of 1943, the GABTU (Main Directorate of the Armed Forces) requested the development of a 55 tonnes (61 tons) heavy tank.
Two factories of the same organization (ChKZ) and the same city, Chelyabinsk, were assigned this task.
1. SKB-2, which was headed by Nikolai Dukhov, who had taken part in the development of the IS tank, and would later become the assistant of the chief designer of the Soviet atomic bomb plan. SKB-2 designed the Object 701, which was a planned upgrade of the IS-2 and later became the IS-4.
2. Experimental Factory No. 100, which was headed by Josef Kotin, who previously had done work on countless Soviet tanks. In contrast to their ‘opponents’, they developed a completely new tank, the Object 252 and 253.
From June to October 1944, Factory No.100’s Object 252 and Object 253 (IS-6) failed in comparison to the SKB-2 design. The armor was much thinner than that of the Object 701, yet it was still heavy, weighing over 50 tonnes (55 tons). The mechanical problems in the suspension and mobility were worse compared to its heavier counterpart. Kotin managed to get the IS-6 to Moscow, where it got tested against the Object 701, but to no avail. In late November of the same year, an upgrade attempt was made with the help of the NII-48 institute using a heavily angled pike-nose design for the armor and a new turret. Despite it being a dead-end when it came to the development of the IS-6, it was a turning point for future heavy tank designs. This is now known as the Object 252U.
Naturally, the design of the 252U was similar to that of the Object 252, as it was based on the same hull. Unmistakable are the large stamped steel wheels with a 750 mm (30 inches) diameter. These were first tested on the Object 244 (an IS-2 upgrade) to be used on the Object 252. The Object 253, although also an ‘IS-6’, used regular IS style wheels. The engine and the rear and side of the hull were untouched on the November improvement. The torsion bars suspension would remain the same too.
The engine would most likely have been the same as on the Object 252, a V12U diesel engine producing 750 hp at 2,100 rpm. The internal fuel tanks had a capacity of 650 liters (172 US gallons) but, in typical Soviet fashion, there would have been 4x 100 liter (26 US gallons) external fuel tanks on the sides.
Interesting to add is that the early designs for the IS-6 actually had a rounded frontal hull, similar to that of the much later Object 279, yet having a similar effectiveness to the Object 252U. The actual prototypes had a hull made of angled flat plates, probably because it was much easier and cheaper to produce compared to a large casting.
The most notable changes appeared in the hull and turret. The NII-48 institute strongly suggested that, in order to improve the protection yet not increase the weight, a pike-nose design should be used. This meant two diagonal plates were welded in the front, creating a pike-like shape and greatly improving the effective armor on the front of the vehicle from threats directly in front of the vehicle. This was designed by engineers G. N. Moskvin and V. I. Tarotko, the latter first incorporated this solution on the IS-2U and on the later Object 257 as well.
Previously, the Object 252 and 253 used the D-30T 122 mm gun. This offered very little improvement over the standard D-25T from the IS-2, yet the price was almost doubled. As a result, a new gun was planned to be added to the Object 252, although it ended up never being fitted. The new gun was the BL-13 122 mm, developed in December of 1943 by OKB-172 and was a combination between the D-25T and the BL-9 gun barrel. Further work was done between Factory No.100 and OKB-172, with the gun being ready by July 1944. The capabilities of this weapon are unknown. A ready rack for the massive projectiles was located in the rear of the turret, covered by a thin protective casing, an overall design similar to modern MBTs. A total of 18 warheads were stored here. The casing with explosive material was stored within the hull, on the exact opposite side. This made loading the warheads relatively easy, however, the placement of the cases required the loader to bend down, and manhandle them up into the breech. One scaled mockup was built of the design.
As the Object 252U was, for the most part, very similar to the IS-6, the crew compartment was mostly identical. It had a crew of four, a commander, gunner, loader and driver. The gunner sat to the left of the gun with the commander behind him. They seem to have shared the same entry and exit hatch, which could be fatal for the gunner in case of a need to evacuate quickly, as he would have to wait for the commander to exit first. The commander had no cupola to look out from, rather just two periscopes (one pointing forwards and the other backward) on top of his hatch. This would have made the commander almost blind when buttoned up. The commander was also in charge of the radio. The loader, as discussed above, had a tough time when loading the main gun. As the cases for the rounds were in the hull, he would have needed to get off his chair and lift them up. Since the turret had no basket, the crew members in the turret could either sit on seats attached to the turret or stand on the hull floor. The loader seems to also have been tasked with the operation of the 12.7 x 108 AA DhSK heavy machine gun. To operate it, the loader had to expose himself, by partially climbing out of his hatch. It is also entirely possible that he was also responsible for loading the co-axial machine gun, a 7.62 mm SGMT. The driver was located in the hull, with the hatch directly underneath the gun, potentially making it very difficult to exit, if the gun was pointing forward.
Since the Object 252U put such a large emphasis on protection, crew comfort and ergonomics were sacrificed. The angling of the hull armor plates made storing ammunition and overall life inside cramped and claustrophobic. An awful thought for many western tankers, Soviet tank design doctrine often sacrificed crew comfort for protection or a low silhouette.
If the IS-6 or Object 252U would have entered service, it would have most likely received a series of upgrades to fix the problems mentioned above, like the periscopes. The Object 701 had its periscopes altered and more added several times until full scale production. However, the armor profile and no turret basket were still features of future Soviet heavy tanks.
It was regarding armor that the IS-6 struggled the most in comparison with the IS-4. The front was one 100 mm (4 inches) thick flat plate angled at 65°. The lower front plate was 120 mm (4.7 inches) thick, yet only angled at 52°. The side armor at the thickest, was 100 mm. Testing was done in Kubinka, Moscow with captured German 88 mm and 105 mm guns, which could not penetrate the upper frontal plate from 50 m (55 yards). The 120 mm lower plate, being less angled, was penetrated from a “shorter distance”. These results, while being better than the IS-2 and IS-3, fell short of the protection offered by the IS-4. In this regard, the new pike nose design of the Object 252U came into play, as the lower plate was still 120 mm thick, but more sharply angled at 28°. The two upper plates forming the pike nose were 100 mm thick, yet angled at 16° from the side. This increased the effectiveness of the armor significantly. The rest of the hull remained the same as that of the regular IS-6.
With the help of NII-48, Factory No.100 also designed the IS-2U simultaneously with the Object 252U, making an IS-2 with a pike-like front hull. An improved version of the IS-2, it featured a new gun, and the pike-nose frontal armor. Like the Object 252, it was rejected, in favor of SKB-2’s Kirovets-1, which later became the IS-3.
Fate and Conclusion
The Object 252 November upgrade got as far as a mockup, as the fate of the IS-6 had already been sealed. Yet, despite being unsuccessful, the design was not in vain. Instead, it served as a basis for the Object 257, which in turn led to the IS-7 heavy tank, the heaviest Soviet tank ever built. More importantly, it was one the first Soviet designs to implement the pike-nose design, which became famous with the IS-3, and was implemented in the majority of Soviet heavy tanks until their discontinuation.
122 mm D-13 2-part ammunition gun
12.7 x 108 mm DShK heavy machine gun on roof
co-axial 7.62 mm SGMT machine gun
Frontal plates: 100 mm forming pike nose at 16°
Lower plate: 120 mm angled at 38°
Upper side plates: 100 mm angled at 45°
Lower side plates: 100 mm at 90°
Upper rear armor: 60 mm at 60°
Lower rear armor: 60 mm at 30°
Upper hull armor: 30 mm
Floor armor: 20 mmTurret armor
Front: 150 mm
Side: 150 – 120 mm
Rear: 100 mm
Top: 30 mm
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