WW2 Soviet Heavy Tank Prototypes

KV-3 (Object 223)

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-220

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.

The KV-220 tank on which the KV-3 was heavily based upon.
Source: Stalin’s Heavy Tank IS-7

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.

Overlay of the 107 mm ZiS-6 (F-42) on the KV-220. Also note the difference in size between the 107 mm and 85 mm shell.

German Threats

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.

The Object 222 was the first tank to be named KV-3. However, this index would later be given to the Object 223, with the 222 being re-indexed KV-6.
Source: Yuri Pasholok, edited

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.

View of the KV-3 mock-up, based on the T-221 hull. Note that this early variant has a DT machine gun in the front of the hull.
Source: Warspot

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.

Side collage of the KV-3 mock-up. The ‘bulge’ in the side turret armor for the commander and his cupola can be seen.
Source: Warspot
View of the KV-3 mock-up, this time showing the rear of the hull and turret.
Source: Warspot

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.

The KV-2 armed with the 107 mm ZiS-6 and KV-3 gun mantlet during firing trials in June, 1941.
Source: Tank Archives

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 100,000
Models and mock-up 50,000
Technical and functional drawings 350,000
Prototype construction and factory trials 1,300,000*
Military trials 150,000*
Drawing fixes/bug fixes 100,000*
Prototype bug fixes and repairs 450,000*
Sum 2,500,000

* 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.

Side cutout view of the KV-3, showing various elements of the tank. Note that this drawing is of the variant with the flamethrower.
Source: Yuri Pasholok, edited
Side view of the hull’s plates with individual connecting pins and welds. Drawing was signed 16 April.
Source: ASKM via Stalin’s Supertanks IS-7
Top view of the hull and engine deck with several connections. Drawing was signed 16 April.
Source: ASKM via Stalin’s Supertanks IS-7
Cross view of the hull and its connections. Drawing was signed 20 April.
Source: ASKM via Stalin’s Supertanks IS-7
Cross view of the return roller on the KV-3. Drawing was signed 16 April.
Source: ASKM via Stalin’s Supertanks IS-7
Cross view of the torsion bar (note that they are cut), swing arms and roadwheels. Drawing was signed 22 April.
Source: ASKM via Stalin’s Supertanks IS-7


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.

Top view of the KV-3 turret, showing the armor thickness and gun mount. Note the coaxial DT machine gun.
Source: Yuri Pasholok, edited
Rear view of the KV-3 turret showing the sharp angled of the side armor, as well as the gun breech and recoil mechanism.
Source: Yuri Pasholok, edited
Internal and side view of the gun mantlet meant to mount the ZiS-6 gun.
Source: Yuri Pasholok, edited
External view of the gun mantlet of the KV-3. This was the same mantlet as the one used on the KV-2 107 mm ZiS-6 testbed. Drawing was signed 29 April.


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.

Top view of the hull of the KV-3 showing various elements from within, such as the engine, final drive, gearbox, fuel tanks or escape hatch behind the driver’s chair.
Source: Yuri Pasholok, edited
The KV-3 transmission designed by N.F. Shashmurin. The document was signed by him on 25 April and then by J.Y. Kotin.
Sources: ASKM via Stalin’s Supertanks IS-7


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). Illustration by Pavel ‘Carpaticus’ Alexe

KV-3 (Object 223) Specifications

Dimensions (L-W-H) 7.85 x 3.42 x 2.95 m
Total weight, battle-ready 67-68 tonnes
Crew 6 (Commander, gunner, driver, radio operator/bow gunner, 2x loaders)
Propulsion V-5SN 12-cylinder diesel, outputting 850 hp w/ AM-38 supercharger
Speed 30-35 km/h
Suspension Torsion bar, 7
Armament 107 mm ZiS-6 (45 shells)
1x 7.62 DT machine gun (60 drums)
1x 7.62 DT machine gun OR 1x flamethrower w/ 15 shots
Armor Front turret: 120 mm
Front hull: 120-115 mm
Sides & rear: 100-90 mm
Top/Belly: 30 to 40 mm
No. Built 1 partial prototype built


Breakthrough tank KV – Maxim Kolomiets
Supertanki Stalina IS-7 – Maxim Kolomiets
Victory Tank KV Vol.1 & 2 – Maxim Kolomiets
Tanks in the Winter War 1939-1940 – Maxim Kolomiets
Constructors of Combat Vehicles – N.S. Popov
Bronevoy Schit Stalina. Istoriya Sovetskogo Tanka (1937-1943) – M. Svirin
TiV No.11 2014 (p.22-24) – I.V. Pavlov & M.V. Pavlov
TiV No.10 2013 (p.10-15) – I.V. Bach
Domestic Armored Vehicles 1941-1945 – A.G. Solyakin
About the forgotten creators of Soviet armored power. ( – S.I. Pudovkin
Малая модернизация КВ | – Yuri Pasholok
КВ-3: набор танковой массы | – Yuri Pasholok
Опытный танк с боевой биографией | – Yuri Pasholok
Tank Archives: KV’s Replacements – Peter Samsonov
Tank Archives: Heavy Trials – Peter Samsonov
Tank Archives: KV-3 Evolution – Yuri Pasholok
Tank Archives: Heavy Tank Costs – Peter Samsonov
Tank Archives: T-150 Revival – Peter Samsonov
Tank Archives: Tank Plans for 1941 – Peter Samsonov
Tank Archives: Mass Breakdown – Peter Samsonov

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