Sunday, 7 February 2016

KV-3: Gaining Weight

After the adoption of the KV-1, it seemed that the upward trend in the weight of Soviet tanks stopped. Instead of the 60 ton SMK and T-100, the Red Army decided on a vehicle that was almost one third lighter and had identical armament and thicker armour. However, work on bigger and heavier tanks in the KV family began in the summer of 1940. The T-220 began trials in January of 1941, a tank that was heavier than either the SMK or T-100. This tank was the harbinger of a series of even heavier vehicles that were meant to replace the KV-1. First and foremost, this was the KV-3.

By Personal Initiative

The 95 mm divisional F-28 gun began trials in 1939. This gun, along with the F-25 122 mm howitzer, would become the "duplex" of divisional artillery. Despite the impressive caliber, the gun turned out very compact while retaining worthy characteristics, including those of an anti-tank gun. The F-28 could penetrate 65 mm of armour at 30 degrees at a distance of one kilometer.

It was logical to develop a tank gun with the F-28's ballistics. The project, initiated by the factory #92 design bureau, was indexed F-39. V.G. Grabin's bureau based their work on the F-34 gun. Periodically, rumours surface that the gun underwent trials in a T-28 tank, and even a photograph is shown, but unfortunately, this is a result of an improper analysis of facts and disinformation by factory #92. The photograph is actually re-touched, a practice common in factory #92 albums. The F-39 was indeed designed and planned to be tested in a T-28, but the gun was never built in metal. By the summer of 1940, interest in 95 mm guns waned, and designers switched to more powerful 107 mm guns.

On June 11th, 1940, a curious item appears in a  list of proposed tank armaments. A new 107 mm gun  based on the corps M-60 gun designed by factory #172 (Molotov, modern day Perm) was proposed as a replacement for the 152 mm howitzer in the KV-2. Trials showed that the M-60 could penetrate 107-110 mm of armour at 30 degrees at 800 meters. This system appears once more in a summary of tank, anti-tank and self propelled guns as "107 mm gun installed in the KV tank turret (oscillating part from the new 107 mm M-60 corps gun)". The due date for this project was November 1st, 1940, carried out by the Kirov factory.

Until now, it was not known the Kirov factory worked with such artillery systems. The design bureau did not take up this work right away, declining it initially. In January of 1941, Kirov factory proposed a high power gun to GAU with the index 412. 400-series indexes were used at the Kirov factory for artillery systems since 1940. For instance, the 152 mm howitzer in the lowered KV-2 turret was indexed 402.

412 was proposed in two variants. 412-1v was a tank version of the naval 100 mm B-24 gun. GAU rejected this design outright. The only parts of the B-24 that were reused were the barrel, shell, and casing. There was no AP shell for this caliber, and GAU fairly insisted that the nomenclature of tank guns should be compatible with field artillery. The first proposal of a 100 mm gun failed.

The second system, 412-2v, had a caliber of 107 mm. GAU proposed that Kirov factory develop this gun at their own expense, as they already refused a government proposal for a 107 mm gun in 1940. Another factory displayed initiative and made this gun by January of 1941. This ends the history of 107 mm guns at the Kirov factory.

It became known in December of 1940 that factory #92 is developing a 107 mm gun on their own initiative. Until then, no information about his new F-42 gun was sent to GAU. The new design used experience with the F-39 and F-34 guns as much as possible. As requested by GAU, the gun used the barrel of the 107 mm mod. 1940 divisional gun (the army designation for the M-60).

It was expected that the F-42 would be ready by December 25th, 1940, but work lagged behind schedule. The new gun was to be tested in the new T-220 heavy tank, but this idea was rejected, as the tank's turret was too small. On February 19th, 1941, Marshal Kulik sent a letter to factory #92 instructing them to install the experimental gun in a KV-2 turret by May 1st, 1941. The tank was already delivered to the factory by January 29th. At the same time, it was decided that an attempt would be made to equip the second T-220 prototype with the F-42, and its turret would be sent to factory #92 for installation.

New Perspective

On March 15th, 1941, USSR SNK and CC of the VKP(b) decree #548-232 was issued, ordering the Kirov factory to prepare the T-150 for production. The improved tank, with factory index 222, would be called KV-3. This was essentially a KV-1 with an F-34 gun, improved turret and commander's cupola, a more powerful V-5 diesel engine, and armour thickened up to 90 mm.

This order did not stand for long. In late March, intelligence revealed that heavy tanks were being built in Germany. It is not known what the spies meant, but the information was taken very seriously. Work on more powerful AT guns began and the KV and T-34 tanks received additional armour. Of course, plans for future tanks were also revised. In mid-April of 1941, work on a new vehicle began, even heavier than the T-150 or even T-220.

On April 7th, 1941, USSR SNK and CC of the VKP(b) decree #827-345ss was issued, establishing the characteristics of the new tank indexed KV-3. The senior engineer of this project was L.E. Sychev, later replaced with B.P. Pavlov. The new tank was indexed 223, occasionally called Object 223. Its mass was estimated at 67-68 tons, its turret armour was 115 mm thick, front of the hull was 115-120 mm thick, sides were 90 mm thick. The armament of the tank consisted of a 107 mm gun and three DT machineguns. The engine would be an 850 hp V-2SN. Until production of the V-2SN got off the ground, it was permissible to use the 700 hp V-5.

Kirov factory was freed from making spare parts for the KV-1, this task was moved entirely to ChTZ. The task of producing the "former" KV-3, now indexed KV-6, would also gradually be transferred there. It's worth mentioning that GABTU was against this decision, proposing that instead of the 223, the T-150 with a 76 mm gun with 3-K ballistics and turret and hull armour increased to 120 mm be built instead.

The new tank did not come from nothing. The KV-3 was a T-150 that was lengthened like the T-220, with a T-220-like turret mounting the F-30 85 mm gun. From the start, the turret would be produced by stamping. Even the experimental hull was not built from scratch. On February 10th, 1941, a set of parts for the T-221 (Object 221) hull arrived at the Kirov factory. This was a T-150 with a lengthened hull that was going to receive a KV-1 like turret with a 76 mm gun. The tank was supposed to be assembled by December 1st, 1940, but Izhor factory was late with parts for a series of reasons and Kirov factory had no time for it either.

Marshal Kulik's aforementioned letter proposed the installation of the F-27 76 mm gun with 3-K AA gun ballistics. This was the second prototype, assembled in the fall of 1940, as it was already called ZiS-5 by spring of 1941. These plans were not to be, as nobody touched the T-221 in February or March of 1941. The same thing happened to the hull of the 212A SPG. In April, it was finally decided that the T-221 hull will be used as a basis for the KV-3. This task was made easier by the fact that the tanks had identical side armour, and only the front had to be thickened.

Design work on the new tank began immediately after the order was received from NKTM. In parallel with the design, trials of the T-220 with a V-5 engine were held. This was the engine meant for the KV-3 before V-2SN production began. The tank, loaded to 70 tons, with the suspension sagging an extra 2-3 cm, drove 150 km between April 12th and April 15th. The missing 150 hp were felt, but the tank could drive, and the V-5 could be used as a temporary measure.

N.F. Shashmurin designed a new gearbox for the tank, a further development of the T-220's gearbox. In parallel, VAMM was tasked with developing an electric transmission. This type of transmission was developed under the direction of Professor N.I. Gruzdev at the academy previously, under its own initiative. Tactical-technical requirements were confirmed on April 29th, 1941. At the same time, requirements for a hydraulic transmission were confirmed. Employees of the All-Union Institute of Hydraulic Machinebuilding were tasked with its design.

By April 26th, a full sized model of the KV-3 was ready, which underwent preliminary inspection. As a result, the rear DT machinegun was removed, and replaced with a PPSh port. It was also recommended that the ZiS-6 (the new name for the F-42) should have a mechanical gun rammer, a travel lock in the rear of the turret, and slight improvements to the turret design. The railroaders made their changes, limiting the width of the tank to 3410 mm. It was also proposed that the round for the ZiS-6 should be one piece and that the ammunition capacity should be increased to 60 rounds.

The second time the commission reviewed the improved KV-3 model was on May 7th, 1941. Along with the model, they inspected a large amount of technical documentation. Aside from minor improvements, one major change was introduced: now, instead of the hull machinegun, the tank could mount a flamethrower designed by factory #174. The tank design was approved, but  a list of a few dozen minor changes was composed.

It's worth mentioning that by now, the KV-3 was treated as a temporary measure. The thickness of its armour was based on the penetration of the 88 mm Flak 18. Looking into the future, even 120 mm of armour was seen as not enough.

Based on results of firing trials of a 105 mm Flak 39 gun purchased in Germany, it was discovered that 130 mm of armour was required for complete protection from this gun. In April 1941, a new even heavier KV-4 tank began development, then the KV-5. Everyone knew that work on the KV-4 and KV-5 would continue on for a long time, and the KV-3 remained a priority for 1941.

According to an addendum to contract #B1-081, signed on June 5th, 1941, the Kirov factory promised to make 500 KV-3 tanks in 1941. The first 55 tanks were to be built in August, then 105 in September, 110 in October and November, and 120 in December. A single tank cost 740,000 roubles. To compare, a KV-1 cost 523,000, and KV-2 cost 558,000. A German Tiger cost 400,000 Reichsmarks, or 840,000 roubles by the 1940 exchange rate. A Tiger II cost 321,500 Reichsmarks or 675, 150 rubles.

Production of the KV-3 was far away. The turret was a big problem, since, as mentioned above, it was to be stamped. As of May 13th, 1941, the tooling for its production was only partially ready, and stamping only began in mid-June. Work on the hull also lagged behind, and it began in June as well. The ZiS-6 arrived at the Kirov factory in May, but trials began in late June. This is how the KV-3 met the start of the Great Patriotic War.

Evacuation

The start of the war quickly made some changes to project work. On June 26th, 1941, NKTP order #253ss was issued, passing the production of the new heavy tank to ChTZ. The same order was sent on June 30th to Kirov factory. The order also cancelled work on the KV-4 and KV-5, but in practice, work on the KV-5 continued until the evacuation. 18 engineering designers were transferred to Chelyabinsk, including Dukhov, Pavlov, and Shashmurin. As for the experimental prototype, it was decided to assemble the hull, give it a production suspension and a T-220 engine. Stamped turrets were sent to Chelyabinsk as well as all tools to make them.

In early July of 1941, the half-assembled KV-3 and its turret were loaded on train platforms and sent to Chelyabinsk. It is said that the history of the tank ends here, since production never started, nor was the prototype ever fully assembled.

In reality, this was not so, as archive documents colourfully describe. It is known that trials of the ZiS-6 started on June 25th, after the start of the war. Trials continued until July 5th, and 618 shots were made. On one hand, trials showed good penetration, 120 mm at 1600 meters. On the other hand, the system underwent criticism regarding the reliability of certain assemblies. Conditional on improvement of reliability, the ZiS-6 gun received a green light.

The work of the factory #92 design bureau did not end here. On their own initiative, a variant of the gun called ZiS-6A was designed. Some authors mistakenly consider it a design for the KV-7 assault tank, but was not the case. What the ZiS-6A really was can be seen in this letter to ChTZ's chief engineer, S.N. Makhonin:

"We developed and are producing a system with a 107 mm ZiS-6 gun and a coaxial 45 mm gun, with the DT machinegun in the previous place. The tactical purpose of this system of obvious, conserving 107 mm shells on targets that could be destroyed with a 45 mm shell.
Due to the absence of a KV-3 at the factory, we are testing this system in a KV-2. Your engineer comrade Schneidman told us that you are making a new turret for the KV-3. Since it is advantageous to have a 45 mm gun in the KV-3 and it only requires minor changes to the turret, we ask you to widen the gun port, and change the frame and mantlet according to the attached blueprints. We do not have blueprints of the new KV-3 turret and are forced to use old ones, but the difference does not matter. At the same time, we ask you to develop an ammunition rack for 107 mm and 45 mm shells, for which we send a dimensional blueprint of a 45 mm shell."

Grabin was proposing to turn the KV-3 into a KV-4 analogue, where two guns (a 45 mm gun and a 107 mm gun) were used in Dukhov's approved design. The letter also suggests that Chelyabinsk was designing a new turret for the KV-3, since there was nowhere to stamp the old one. Sadly, by September of 1941, ChTZ had better things to do than work on the KV-3, as after the evacuation of the Kirov factory, it became the sole producer of KV-1s.

Nevertheless, it was too early to speak of the death of the KV-3. First of all, the tank was still the chassis of the 212A bunker buster, which was not cancelled. Second, the KV-3 remained in experimental work documents of ChTZ (ChKZ from the end of the year). In the plan for 1942, approved on December 22nd, 1941, the KV-3 is first, listed as work that's being transferred from the previous year which, at the very least, should be completed by assembling a prototype. The due date is May 1st, 1942. By December of 1942, a new 1200 hp two-stroke diesel engine based on the V-2 should be ready.

Unnecessary Heavy

The tank's older brother, the KV-1, dug the KV-3's grave, or, more specifically, the unreliable transmission did. Due to the thickening armour and increasing weight, the KV-1 was pursued by breakdowns. The gearbox had the most problems. In the spring of 1942, orders from above dictated that the mass of the KV-1 needs to be decreased. In these conditions, nobody needed a 70 ton KV-3.

Unfortunately, the KV-3 was never built or tested. Not because the 70 ton tank could change the course of the war, despite surpassing every foreign tank. The powerful armour would make the KV-3 a tough nut for the Germans to crack, but that was not the benefit. The main benefit was that the assembly and trials of even one of these tanks could be a wake-up call for the military, knocking off the desire for something similar once and for all.

The result of the trials could be predicted by the issues that the testers and designers of the lighter T-220 ran into. It would have been clear that such a monster could not have been pulled off the battlefield by any recovery vehicle and that transporting it on railroads would be problematic. If our tank designers earned this experience in 1941 with the KV-3, there would be no IS-7 or IS-4. The lesson that a heavy tank should not surpass 50 tons could have been learned in the early 1940s and not in 1949, after 4 years of mucking around with the IS-4 and IS-7. Sadly, history doesn't know the word "if".

Original article by Yuri Pasholok.

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