In response to your letter No. 281377 of August 25, 1941, we inform you that the Ural Heavy Machinery Plant has the design staff needed to begin work on the task assigned by you and signed by Marshal of the Soviet Union Comrade Kulik to develop a self-propelled gun (a bunker buster).
Because Ural Heavy Machinery Plant employees have not previously worked on topics of this type, and the plant has no materials on this or similar topics, to assure a proper and timely solution of the problem, the following materials must be sent to them or the appropriate organizations instructed to send them:
1) Drawings, models, and descriptions of similar foreign systems;
2) The same for heavy tanks;
3) The following materials:
1. A full set of the drawings for the KV-3 tank, and
2. A full description of the KV tank and its equipment.
3. Complete technical specifications for the KV tanks.
4. The complete set of engineering analyses done on the KV tank.
5. All drawings and engineering analyses of the BR-2 152 mm gun traversing mechanism.
6. Drawings of the DT machine gun.
7. Drawings of the PPD submachine guns.
8. Drawings of the PT-1 and KT-1 sights.
9. Description of the PT-1 and KT-1 sights.
10. Drawings of the fixture or storage racks for the M-10 152 mm tank howitzer projectiles.
4) Samples of the following:
1. DT machine gun.
2. PPD submachine gun.
3. PT-1 sight.
4. KT-1 sight.
5. All other devices.
6. Flags.
Please instruct the Chelyabinsk Factory to allow a team of designers from our plant to observe the KV-3 and KV tanks during testing.
Also, please instruct the Chelyabinsk Factory’s special design bureau and the factory that manufactures the engines to support the necessary consultations between our designers and the designers of the engines for the system.
We believe it is especially important that you order a captured heavy tank sent to the Ural Heavy Machinery Plant so that our designers, production engineers, and production workers can study it while developing the system.{2}
The tank industry was not prepared for the KV-3 in October 1941, much less for the bunker buster based on it. The Kirov Factory had been evacuated to Chelyabinsk (and renamed the Chelyabinsk Kirov Factory, or ChKZ for short), as had the Izhor Factory, which produced the KV’s armor. UZTM was temporarily given the name Izhor Factory. Its original name was only restored on January 4, 1942. An additional item on UZTM’s plate was the evacuation of the Kalinin Factory No. 8 and the Ordzhonikidze Factory No. 37 (Moscow) to the plant’s grounds in the fall of 1941. Factory No. 75 which had developed the V-5 engine, was evacuated to Chelyabinsk, and its main mission was to begin producing the V-2 diesel engine, the need for which was much greater. The situation with production of the BR-2 152 mm guns was no better: the last guns of that type had been manufactured in 1940 by Factory No. 221 (“Barricades” in Stalingrad, now named Volgograd).
The bunker buster project was dropped as a high-priority task, but not for long. The system showed up again in GAU correspondence in November 1941. A report by Military Engineer 2nd Class Getmanov (of the Field Artillery Armament Directorate’s Main Artillery Directorate) discussed work done in Chelyabinsk from November 12 through 24, 1941:
During this period it was found that:
a) As regards the issue of artillery prime movers:
State Defense Committee Decree No. 899ss dated November 14, 1941, instructed the People’s Commissariat of the Tank Industry (NKTP) to expand the production of tanks, for which purpose a number of factories have been transferred to the NKTP from other Commissariats, including all tractor plants.
State Defense Committee Decree No. 982 of November 13, 1941, relieved the Kirov Factory (ChTZ) of responsibility for manufacturing artillery tractors (the S-2) and agricultural tractors (the S-65).
State Defense Committee Decree No. 892 is understood by the People’s Commissariat of the Tank Industry as giving it the right to cease tractor production at other factories as well (the Voroshilovets at Factory No. 183, and the STZ-5 at the Stalingrad Tractor Plant).
Therefore, production of tractors has ceased.
The situation with artillery prime movers was bad before this, but after this decision artillery may be left without prime movers.
I believe the People’s Commissar of Defense, Comrade Stalin, should be informed about this situation.
b) As regards the issue of self-propelled guns:
A study of this issue for a report prepared for Comrade Kotin, Deputy People’s Commissar of the Tank Industry at the People’s Commissariat of the Tank Industry and with designers at UZTM and the Kirov Factory, came to the following conclusions:
I. The work schedule of the People’s Commissariat of the Tank Industry for 1942 includes the following self-propelled guns:
1. A bunker buster mounting the BR-2 152 mm gun on a chassis incorporating assemblies from the KV tank.
2. A tank destroyer mounting the 85 mm antiaircraft gun on a chassis incorporating assemblies from the T-34 tank.
3. A regimental assault gun mounting the 76 mm USV or the ZIS-3 on a chassis incorporating assemblies from the T-60 tank.
4. Self-propelled antiaircraft guns:
a) A 37 mm gun on the T-60 tank
b) A 25 mm gun on the T-60 tank
c) A 37 mm gun on the T-50 tank
d) A 37 mm gun on the T-34 tank
Comrade Kotin has accepted the recommendations for these self-propelled guns and stated that he would issue the appropriate orders to the factories.
I believe it is urgent that an operational requirement be sent to the People’s Commissariat of Medium Machine Building and the factories, that a GABTU representative visit the People’s Commissariat of the Tank Industry, and that the systems listed in the work schedule be pursued. A liaison visit should be made to the factories that are beginning work on the projects and appropriate advice should be given.{3}
This letter marked the initiation of wartime development of SP guns. Beginning in November 1941, work intensified on many of the SP gun projects named in the draft decree of the Council of People’s Commissars of the USSR and the Central Committee of the All-Union Communist Party (Bolshevik) “On Self-Propelled Artillery” that was issued on May 27, 1941. Operational requirements were still being drawn up prior to 1942; however, conceptual designs were not even being discussed. Most of the factories assigned to develop SP guns were either still in the process of setting up production lines at the sites to which they had been evacuated in the summer and fall of 1941, or they had been loaded down with more urgent orders. Nevertheless, the development plan for 1942 again featured the “KV-3 Tank” project with a completion date of May 1, 1942. The project also included a “1200 hp two-stroke diesel engine” (with a completion date of October 1, 1942) and a “supercharged 1200 hp V-2 diesel engine” (to be completed by July 1, 1942).
The project bearing the title “A 152 mm Self-Propelled Gun Incorporating Assemblies from the KV Tank Chassis” (a bunker buster) surfaced again in March 1942. The KV tank was specified as the base chassis, and the armament was to include the tipping parts from the BR-2 gun. Pilot Plant No. 100 (established in Chelyabinsk in 1942) of the People’s Commissariat of the Tank Industry was given responsibility for the chassis, and Factory No. 8 of the People’s Commissariat of Arms at its new location in Sverdlovsk was to be responsible for the gun. The amount allocated for development was 1.5 million rubles, and a prototype was expected by July 1, 1942. However, the KV-3 project was finally killed in the spring of 1942, and an entirely different vehicle began to be considered as the base chassis for the bunker buster.