Tank design in the 1930s Soviet Union was a period of great experimentation and versatility, with designs ranging from jumping and flying tanks to super heavy multi-turreted ones. Yet as the Soviet tank industry matured, tank designs became more sensible and, by the late 1930s, some very promising vehicles were in development, such as the T-34 and KV-1. Nevertheless, with tensions rising in Europe after the German invasion of Czechoslovakia, Poland, and then France through the Benelux, Soviet engineers had to fall back to some older drastic ideas. One of these was the KV-4, one of the most curious heavy tank programs in Soviet tank history, as it involved a competition between dozens of designers.
On 11th March, 1941, the GABTU (Main Directorate of Armoured Forces) was informed by the Soviet Intelligence services of the existence of new German heavy tank projects. The report, naturally, was a mixed bag of real information and rumours. It is important to note that, while the Soviet Union and Nazi Germany were more or less allies during this period, tensions were high and any sort of technological advancement of the opposition had to be met with a proportional (or, in this case, disproportional) response.
The document received was titled “The direction of development of the German armed forces and changes in their state” and discussed several tank projects. When it came to heavy tanks, a chart presenting 3 tank models was shown:
- Mark V (36 tonnes, 75 mm gun, 2x machine guns, ≤ 60 mm of armor)
- Mark VI (45 tonnes, 75 mm gun, 20 mm gun, 3x machine guns, ≤ 70 mm of armor)
- Mark VII (90 tonnes, 105 mm gun, 2x 20 mm gun, 4x machine guns, unknown armor)
The report also mentioned, based on unconfirmed information, 72 tonne French tanks (possibly the Char 2C, which weighed 69 tonnes) present at the occupied Renault factory, in addition to 60 and 80 tonne tanks being built at Škoda and Krupp.
On the one hand, the Germans had indeed begun development of several heavy tanks, such as the 30-and 36-tonne projects (VK30.01(H) and VK36.01(H)). A month after the original Soviet report, in May, the Germans decided that, for 1942, the armor of future heavy tanks had to be improved. This would consist of 100 mm of frontal armor and 60 mm at the side. In terms of heavier vehicles, the VK.65.01 appeared in January 1939.
Interestingly, the Pz. Kpfw. VII, commonly known as the Löwe, with its many variants and stages, would not appear until November of 1941, with development starting in December. Mentions of a tank armed with a 15 cm L/40 existed earlier on. This begs the question on what the Soviet report was based on. It was very likely a combination of several tank designs and proposals, alongside rumours and speculations, likely cherry picked to sound as alarming as possible.
To put things into perspective, during this period, the best heavy tank in Soviet service was the KV-1, armed with the 76 mm L-11, meant as a stopgap until the introduction of the F-32 gun, which was not a significant improvement anyway. These guns were seen as problematic, especially by armament designer V.G. Grabin, but the political rush to push the KV-1 into production and military service left it with considerable faults and problems, including the armament and the infamous gearbox, which, it must be noted, was designed by N.L. Dukhov himself. The most important aspect of the KV-1 was its armor, with 90 mm at the front of the turret and 75 mm at the front of the hull. By 1941, the Soviets had several improvements of the KV-1 in the works, including the T-150 and KV-220, which brought more armor and better armament. With hindsight, the KV-220, with its 85 mm F-30 gun and 100 mm of armor all around, would have been (on paper) on par with the German Tiger I, which entered production only in August of 1942, 1.5 years later. It seems it would have been rather reliable, running 967 km with the V-5 700 hp engine (only needing 2 idlers, a torsion bar, 6 idler axles replaced and shearing 2 teeth in the transmission and destroying the eyelet of the clutch) after the 2 V-2N supercharged experimental engines broke.
Nonetheless, the Soviet authorities did not take the report lightly and immediately ordered work on an even heavier tank. It was expected that the gun used would be the 105 mm Flak 39. The Soviets had previously purchased this gun in 1940 for testing and, after firing trials, it was noted that a tank required 130 mm of armor or more to withstand fire from it. The Kirov Leningrad plant’s SKB-2 design bureau was tasked with the design of the new tank. At the same time, they were working on the KV-3, at the time a 50-tonne heavy tank, already superior to any German tank at the time. The Kirov plant had also worked on the T-150 and KV-220 tanks, which were further developments of the KV-1.
Design and technical requirements were given only 10 days after the initial report, on 21st March, 1941. The new super heavy tank was named KV-4 (the acronym KV stands for Kliment Voroshilov, People’s Commissar for Defense of the Soviet Union until 1940) and received the GABTU designation Object 224. It was to weigh around 70 to 72 tonnes, with a frontal armor of 130 mm, side armor of 120 mm, and 40 mm on the belly and top. The main armament was to consist of the ZiS-6 F-42 107 mm gun. It was meant to have a full traverse range of 360° (though a handful of designs would mount the gun in a casemate with limited traverse). Elevation was to be between 15° to 17° and depression between -2° and -3°. Secondary armament would consist of 3 DT machine guns; one coaxial, one in the turret bustle and one at the front of the hull. Mounting of a 76 mm ZiS-5 gun was also desired as an alternative to the ZiS-6, though this was eventually dropped. A flamethrower was also mentioned for protection against approaching infantry.
The powerplant was meant to be a 1,200 hp engine, with the tank reaching an estimated top speed of 35 km/h. However, since there were no such powerful engines available at the moment, the 850 hp V-2SN was to be used as a temporary fix. For the KV-5 (and potentially the KV-4 as well), mounting 2 V-2SN was also considered until the M-40s were ready. Eventually, LKZ managed to produce 58 M-40 engines by August. Another variant was considered, the M-50, giving out 1,000 hp, which was meant for torpedo boats. The fuel was meant to last for 10 hours of continuous driving, in conditions between -40° and 40° Celsius. The gearbox had to be an automatic planetary type and the brakes had to hold up the tank’s weight on a 45° slope angle. The crew was to be composed of 6 men: Commander, gunner, loader, turret mechanic (loader assistant), driver, and radio operator, with the last two in the hull.
On 27th March, the Council of Ministers of the USSR released the plans for the development of the heavy tanks, presenting the deadlines of the development process. The LKZ plant was to provide drawings by 17th July, Plant No. 92 to deliver a 107 mm ZiS-6 and 76 mm ZiS-5 by 1st September and Izhora plant in Leningrad to build the hull and turret by 1st October. In terms of powerplants, the V-2SN and M-40 engines were considered. From a letter dated 30th May, the development (from blueprints to prototype testing and improvement) of the KV-4 was expected to cost 3,100,000 Roubles, while the KV-5 was estimated at 3,600,000 Roubles. Just the construction and factory trials of the KV-4 were estimated at around 1,800,000 Roubles. To put this into perspective, the production of a single KV-1 was around 295,000 Roubles (May 1942).
In an interesting turn of events, by 7th April the plans were changed entirely. The KV-3 program was revitalized, with the weight increased to 68 tonnes, armor increased to 120 mm and mounting a 107 mm gun. Consequently, in a letter to LKZ factory director I.M. Zaltsman, the KV-4 requirements were increased to a weight of 75 tonnes, 135 mm (some sources claim as much as 140 to 150 mm) of armor on frontal areas, and 125 mm on the sides and rear. The deadline for the blueprints was brought forward to 15th June. The hull and turret were expected on 15th August. Simultaneously, the KV-5 was brought to life. It was to be a response to the so-called ‘Pz.Kpfw.VII’, with a mass of 90 tonnes, frontal armor 170 mm thick, and 150 mm thick on the sides. It was to be built by 10th November.
The turrets had to be of welded and stamped construction, as castings at these thicknesses were not technologically possible at the time. Another issue with the armor was the connection. The Soviet armor industry could barely handle welding 75 mm armor plates, let alone anything above 125 mm. This issue was partially solved on the KV-5 (which got further into its developmental stage), where steel rods would be pushed and welded in holes drilled through the two armored plates, which in turn would be laid onto one another.
The main gun required between 70 and 80 rounds of ammunition. To top it all off, in a letter from the chief or the Main Auto and Armour Directorate of the Armoured Forces to the LKZ and Izhor factories, the prototypes of KV-4 (and KV-5) were expected to be completed and enter the testing phase by 1942.
Work began on the KV-4 at Kirov on 10th April. The head designer was J. Y. Kotin. Considering that the tanks were to be designed from scratch, Kotin decided upon doing a competition. After getting Zaltsman onboard, they decided to even give prizes for the best designs. Most of the engineers at the Kirov SKB-2 design bureau would participate in the competition. No details were given about the layout, prompting a variety of unique and creative designs. However, a bit of confusion seems to have risen regarding specific details, as the specifications set up at LKZ did not entirely match the ones requested by the GABTU. The mass was set between 80 and 100 tonnes, armament consisting of the ZiS-6 107 mm and a 45 mm gun mod.1937, with the second gun meant for zeroing in the main gun and for dealing with softer targets. The Soviet military allegedly requested a flamethrower as well, but some designs lack it.
By 9th May, the competition was over and the winners were announced. Between 24 and 27 different designs were submitted (excluding different variations of the same design). In first place came N.L. Dukhov, who received 5,000 Roubles. Second place was given to a design made by 3 engineers, K.I. Kuzmin, P.S. Tarapanin, and V. I. Tarotko, who received 3,000 Roubles to be split between them. On third place came N.V. Zeits, who received 2,800 Roubles. The list continues to the 7th spot, with many places having several designs. Unfortunately, some designs have been lost to time, and some designs have unknown authors, or some lost drawings. From the 11 ‘winning’ designs, only Kalivoda’s project is missing blueprints. Kotin himself received 3,100 Rubles for leading the engineering team.
|Designer name||Place||Prize received (Rubles)|
|K.I. Kuzmin, P.S. Tarapanin and V. I. Tarotko||2||3,000|
|N.V. Zeits||3||2,800 (2,000 according to another archive document)|
Other engineers who presented designs but did not receive any awards were F.A. Marishkin, S.V. Federenko, M.I. Kreslavsky, V. Pavlov and D. Grigorev, P. Mikhailov, G. Turchaninov, N. Strukov, and 2 other unnamed designers.
Despite the exciting competition, the progress was slow. By 12th June, 3 days prior to the deadline, Marshal of the Soviet Union G.I. Kulik sent a letter to LKZ demanding the speed-up of the design process. Yet the drawings were never submitted. Just 10 days later, on 22nd June 1941, German forces began their invasion of the Soviet Union.
The GABTU decided that the KV-3, which was in an advanced stage, would continue development and be implemented as a stopgap measure until the KV-4 and KV-5 were ready. These two would be tested against each other and the winner would be produced. Development of the KV-5 continued until August, albeit at a much slower rate, when the Germans had already reached Leningrad. The workers and engineers at LKZ, including SKB-2, were moved to ChKZ in Chelyabinsk.
In a decree dated 18 April 1941, from the Council of Comissars, a KV-4 based SPG was mentioned, having 60 mm of armor and a lengthened KV-4 chassis (why lengthening the chassis was deemed necessary is a mystery). It was to be armed with a 107 mm gun using a 152 mm ML-20 mod.1937 howitzer gun mount, and was to have a muzzle velocity of 1100 m/s, developed and produced at plants No. 172 and No.92. Theoretical calulations from the time gave the armament a penetration of 188 mm, angled at 30° from 1000 m. Later calulations reduced the muzzle velocity to 1020 m/s. The first experimental guns were expected by 1 July. Work was carried on in parrallel to the Object 212 and SU-B-13 SPGs, but the KV-4 SPG never reached the blueprint stage.
N. L. Dukhov
The winner of the KV-4 competition, Nikolai Leonidovich Dukhov, was born in 1904 in Veprik, in modern day Ukraine. He was behind several Soviet tank projects. In his first years as an engineer, he worked at the Putilovets tractor factory, on the Universal tractor. In 1936, he worked on his first tank project, a modernization of the T-28. A few years later, his team at the LKZ (Kirov) SKB-2 design bureau was responsible for designing the KV-1 heavy tank. After the Siege of Leningrad, SKB-2 was moved to ChKZ, from where he continued designing tanks. Other noteworthy tanks designed under his leadership were the KV-1S, KV-2, KV-85, KV-13, IS, IS-2, IS-3, and IS-4.
After 1948, he was involved in the Soviet nuclear program, being deputy chief designer at KB-11 (since 1992 known as the ‘Russian Federal Nuclear Center’) and participated in the development and testing of the RDS-6s thermonuclear hydrogen bomb, with a yield between 400 to 500 kt. In 1954, he became chief director and supervisor at branch No.1 of KB-11, which still bears his name to this day. He led it until his death in 1964, at just 59 years. He received 3 Hero of Socialist Labour medals, 4 Lenin Orders, 5 Stalin Prizes, the Lenin Prize, the Order of Suvorov, the Order of the Red Banner of Labour, the Order of the Red Star, the medal for Labour Valour, the Medal For the Victory over Germany in the Great Patriotic War 1941–1945, the Medal for Valiant Labour in the Great Patriotic War 1941–1945, the Jubilee Medal 30 Years of the Soviet Army and Navy, and the Jubilee Medal 40 Years of the Armed Forces of the USSR.
Dukhov presented at least 4 drawings of his proposal, one side view of the entire tank, one cutout top view of the turret, one partial cutout of the hull and one showing the automated round lifting system. The design was very similar to the KV-220, a tank designed with L.E. Sychev and B.P. Pavlov (both of whom submitted KV-4 designs), but much larger. The hull was essentially an up-armored and lengthened KV-1 hull, with 8 wheels per side, sprung by torsion bars. Other details and components remained mostly identical to those of previous prototypes and of the KV-1 mod.1941. The exact number of return rollers is unknown, but comparing to previous designs, 4 appears most likely. Curiously, the rear engine deck plate was angled downwards, similar to the KV-1S. His design was the lightest of all KV-4 designs, estimated at ‘just’ 82.5 tonnes.
One of the engines considered was the M-40 aviation diesel engine, developed at LKZ (after the original designer, A.D. Charomsky, was arrested in 1938, during the Purges). It had an output of 1,000 horsepower (later improved to 1,200) with 12 cylinders arranged in a V-shape, and 4 TK-88 turbochargers. There was also an upgraded version, the M-40F, delivering up to 1,500 hp. The other engine considered was the V-2SN, which was an upgraded variant of the classic V-2 12 cylinder engine. It was boosted with a turbocharger to 850 hp. With such a powerplant, Dukhov expected his design to reach an optimistic 40 km/ top speed.
The turret designed by Dukhov was also similar to the KV-220, with the main difference being that the frontal plate (mostly covered by the mantlet) was angled, as opposed to flat like on previous KV tanks. A total of 4 plates were used for the turret, with the frontal plate angled at circa 20° and 130 mm thick. The side armor plate would have been circa 125 mm thick and stamped into shape. The rear plate was flat and 125 mm thick. On top of the main turret, a smaller turret was added armed with a DT machine gun. This turret had circa 3 vision periscopes for the commander. Another 4 periscopes were scattered around the turret to give vision to the rest of the crew members.
In terms of placement of the 6 crewmen, the driver and radioman were placed in the hull, in identical positions to other KV series tanks. The gunner was seated to the right of the 107 mm gun, while the commander was standing behind him, operating the cupola. As for the loaders, one was seated to the right of the 45 mm gun and was tasked with loading it and lifting ammunition for the 107 mm. The other loader was standing behind the main gun and had the task of loading the main gun. They used a 10-R intercom for communication between each other.
The KV-4 used the F-42 ZiS-6 107 mm as the main gun. It was designed by the iconic V.G. Grabin at factory No.92. First appearing in documentation in December 1940 as the F-42, but renamed to ZiS-6 in March 1941. The gun was ready by 14th May, taking only 38 days to design according to Grabin himself, after both Marshal of the Soviet Union Kulik and Stalin spoke to Grabin about the issue, though a phonecall between Grabin and Stalin revealed that the gun had to be designed in 45 days. Plant No-92 was forced to work ahead of schedule, and on 27th May, sent a gun to LKZ for mounting on the KV-2 for testing. Yet the Izhora plant, tasked with making the turret for the test ring, using a KV-3 gun mount, was progressing very slowly. On 18 June, Marshal Kulik had to intervene (again), for the Izhora plant to finish the turret. Testing finally began on 25th June and ended on 5th July. After the initial test, faults were fixed, and the gun was deemed ready for production. Serial production began at the New Sormovo plant in July. But, according to Grabin’s memoirs, the lack of cooperation and work from the tank factories was a large dissapointment.
The production of the ZiS-6 increased daily. But there was still no sign of the tank for which the gun was intended. Even after the beginning of the war, the Kirov plant did not deliver a single tank. The lack of the new tank forced us to limit production and eventually, cancel it. It is difficult and embarrassing to write about this, in those days when everything that could shoot, even museum pieces, were sent to the front, around 800 gun barrels had to be sent back to the melting furnace
– V.A. Grabin, extract from his memoirs.
In September, the ZiS-6A was discussed for the KV-4, which involved the mounting of a 45 mm gun coaxially, but it remained just an idea, mostly because of the abandonment of the KV-4.
In terms of technical data, the ZiS-6 had an muzzle velocity of 800 to 840 m/s. Ammunition was one-piece and weighed 18.8 kg. The breech lock was mounted vertically and was semiautomatic. It could allegedly penetrate 115 mm of armor at 1,000 m.
Regarding secondary armament, Dukhov fitted his design with a coaxial 45 mm mod.1937. With a muzzle velocity of 750 m/s, it would be used for ranging in the main gun, while also engaging targets that would not require the main 107 mm gun. Loading would be done by any of the two loaders. There was no firing mechanism designed for it, but it was likely fired independently from the main gun by the gunner. The tank also had at least two DT machine guns, one mounted in a ball mount in the hull, and the other in the secondary turret on the top of the main turret. Ammunition for it was stowed in the hull, on both sides of the turret ring.
Dukhov had envisioned 2 ways to load the main gun. The first was the classic way, by simply lifting the ammunition stored in the floor of the tank’s hull. There must have been a form of turret floor, as the entire hull floor was peppered with ammunition. This was in no way a simple endeavour, but with two loaders, it was a realistic task. The second option was a semiautomatic loader system, which had a system that would lift up the shells from the hull to the same level to the gun breech, from where the loader could load them in. The shells would be lifted by a chain-like system, in-line with the gun breech. These would be stored across the hull, and would have been required to be placed manually in the lifting system.
Even after the German attack on the Soviet Union, work on tanks continued at LKZ. For the KV-5, the engineers who had received the top places in the KV-4 competition (except the 3 in second place) would work together on the KV-5. This gained traction and blueprints were being drawn, including the turret, hull and running gear components. As for the KV-4, there was barely any progress. Dukhov’s design was awarded as the best, but what this truly meant for the KV-4 is all speculation. Whether Dukhov’s would have been the main layout of the final KV-4 prototype is unknown. Work continued on the KV-5 and KV-3 until August, by which time the Germans were quickly approaching Leningrad. To deal with this, the SKB-2 design bureau was evacuated to ChKZ in Chelyabinsk. There, work on the KV-4 and KV-5 would not resume, as they were seen as a large waste of time and money when the Soviet Union needed tanks yesterday.
With the KV-1 seeing combat against the Germans, it was truly confirmed how unprepared for service it truly was. Dozens of reports came in about transmission and gearbox failures, the vehicle being too heavy and slow, and crews preferring the T-34. The situation got so serious that Stalin himself said that, if the issues would not be fixed, the KV production would be discontinued. This obviously came as a serious blow to LKZ engineers, which immediately began improving the KV.
Additionally, the conspired German heavy tanks never came. Thus, all unnecessary heavy KV projects were left behind and work was focused on improving the KV-1. The work eventually resulted in the heavily praised KV-1S, experimental KV-13 and, finally, the iconic IS.
Arguably one of the most interesting Soviet heavy tanks of the Second World War, the KV-4 was not just a massive vehicle, but also involved the interesting competition tactic which would not be applied again by Soviet designers. This brought a variety of interesting and unique ideas. However, no matter how advanced or revolutionary the KV-4 designs were, the entire program was simply too expensive and worthless, especially once the Soviets had entered war against the Axis. The program was not without its merits.
Dukhov’s KV-4 incorporated an efficient and trialed design into what was seen as the most successful KV-4 variant. It was the lightest, simplest, and almost a natural evolution from the KV-220. Equally interesting, he envisioned a partially automated loading system, with shells being lifted to the level of the gun breech. This gave him the victory against all the other engineers, but it was to no avail.
KV-4 Dukhov’s variant specifications
|Dimensions (L-W-H)||8.150 – 3.790 – 3.153 m|
|Total Weight, Battle Ready||82.5 tonnes|
|Crew||6 (Commander, Gunner, Driver, Radio operator, loader & turret mechanic/loader assistant)|
|Propulsion||1,200 hp diesel V-12 M-40 with 4 turbochargers|
|Speed||40 km/h (hypothetical)|
|Suspension||Torsion bar, 8 wheels per side|
|Armament||107 mm ZiS-6 (F-42)
45 mm Mod.1937 coaxial
2x DT machine guns
|Armor||Front top plate: 135 mm
Front bottom plate: 130 mm
Side plate: 125 mm
Top and belly: 40 mm
|Total Production||0; blueprints only|
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