Compared with these designs, the idea of developing a bunker buster using the KV-7 hull looked much more reasonable. At the time, development of the twin 76 mm gun system assigned by the State Defense Committee’s January 6, 1942, Decree No. 1110ss was a higher priority task. Yet at the same time the requirement for an upgraded version of the KV-7 was issued, S. G. Ginsberg also drafted a requirement for a 152 mm SP gun based on the KV-7 chassis:
The 152 mm SP howitzer shall be designed using the KV-7 tank and shall be an artillery weapon for close-quarters destruction of bunkers in fortified regions.
I. Combat weight of the SP gun: 50–55 tonnes
II. Armor:
Armor protection for the hull and system: same as the KV-7 tank
III. Armament:
1. 152 mm howitzer: 1
- Twin gun traverse angles: +/-7.5°
- Elevation angles: +12° -5°
2. Number of DT machine guns
a) In the bow: 1
b) In the rear of the fighting compartment: 2
- Machine gun traverse angle: 30°
- Machine gun elevation angles: +15° -5°
IV. Basic load:
1. Projectiles for the 152 mm howitzer: at least 30
2. Number of machine-gun drums: at least 40
V. SP gun crew: 6
VI. SP gun hull.
The SP gun hull shall be the same as that of the KV-7 tank, except for parts directly associated with installation of the howitzer.
VII. Fighting compartment and armament installation
1. The fighting compartment must allow for convenient placement of the gun crew and have instruments for 360° observation.
2. The fuel tanks may be located on the bottom of the fighting compartment to increase the amount of ammunition that can be carried and its convenient location.
3. To increase the rate of fire and facilitate loading of the howitzer, it is desirable to at least partially mechanize the loading process (feeding the projectile and charge).
VIII. The tank’s mobility, engine, suspension and communications equipment must be similar to that of the KV-1.
Note: the factory may alter and supplement this operational requirement to improve the design in coordination with the People’s Defense Commissariat, the Armor Directorate of the Red Army and the People’s Commissariat of the Tank Industry.{2}
In the development plan for 1942 approved by People’s Commissar of the Tank Industry Malyshev on January 21, the system would proceed under the number 59. According to the plan, the Kirov Factory (ChKZ) would be responsible for the bunker buster’s chassis, and the Ural Heavy Machinery Plant would answer for the artillery system. The design drawings were expected by March 15, the prototype by May 1, and the production drawings by May 10. The amount allocated for the project was 300,000 rubles. That was not a large sum compared with the amount allocated for Project 212. However, it involved modifying existing KV-7 assault tank hulls, not developing a vehicle from scratch.
This project produced a mixed reaction at the GAU. People there continued to insist on developing a “BR-2 152 mm gun on a chassis incorporating assemblies from the KV tank.” The idea of developing an SP gun based on the KV-7 was considered lacking. That is evident, for example, from the letter GAU’s chief, Col. Gen. of Artillery N. D. Yakovlev, and GAU Military Commissar Kozlov wrote to L. P. Beria, Deputy Chairman of the Council of People’s Commissars of the USSR on March 25, 1942:
Our experience in this war and the war with Finland has revealed the following characteristics of modern military operations:
1. Massive use of highly mobile armored and mechanized equipment;
2. In-depth reinforcement of strategic lines with reinforced concrete bunkers and earth-and-timber emplacements.
These circumstances have given rise to new requirements regarding the mobility of artillery of all calibers and purposes and its capability for conducting direct fire.
The mobility of equipment used to tow artillery lags far behind the mobility of modern tanks. The average speed of artillery prime movers is no greater than 10–12 km/h and agricultural tractors are no faster than 5 km/h, while tanks are capable of speeds in excess of 40 km/h.
In addition, corps-level and heavier artillery pieces are completely open, making it difficult to use them for the close-quarters destruction of bunkers.
We need to develop highly maneuverable artillery systems that are also adequately protected against short-range fire.
This can be self-propelled artillery incorporated into armored auxiliarypropelled hulls that share components with tanks currently in production.
Foreign armies possess mobile armored self-propelled guns.
I believe we need to have three types of self-propelled artillery systems:
1. Self-propelled artillery for destroying bunkers.
2. Self-propelled artillery for destroying tanks.
3. Self-propelled assault artillery for supporting mechanized forces.
4. Self-propelled antiaircraft guns.
Development of the following self-propelled systems must be organized at industrially capable artillery and tank factories:
1. A bunker buster mounting the BR-2 152 mm gun on a chassis incorporating assemblies from the KV tank.
2. A tank destroyer: 85 mm antiaircraft gun model 1939 on a chassis incorporating assemblies from the T-34 tank.
3. A self-propelled assault system: ZIS-3 or USV 76 mm gun on a chassis incorporating assemblies from the T-60 and T-70 tanks.
4. A self-propelled antiaircraft system: 37 mm automatic antiaircraft gun on T-34 and T-60 or T-70 tanks.
Operational requirements for development of these prototypes have been sent to the factories and the People’s Commissariat of the Tank Industry, but not all of the projects stipulated in the GAU’s plan have been acknowledged.
The People’s Commissariat of the Tank Industry has decided not to arm the bunker buster with the BR-2 152 mm gun, but rather to equip it with the ML-20 gun-howitzer, which is significantly less capable of penetrating concrete and armored turrets.
In addition, the People’s Commissariat of the Tank Industry is refusing to develop tank destroyers, citing development of the 85 mm tank gun for the KV tank as the reason.
Given the urgent need for development of these self-propelled systems, I hereby request that Comrade Malyshev, People’s Commissar of the Tank Industry, be ordered to undertake these projects.{3}
However, the desires of the artillerymen in this case were at cross purposes with a number of obvious facts. Project 212 had been shut down by the spring of 1942, and the Chelyabinsk Kirov Factory had no plans to revive it. The same was true of the KV-3, the chassis used for the development of the bunker buster. Even if the Council of People’s Commissars insisted on this SP gun, there was absolutely no way a prototype could be built or the system could be put into production. Revival of production of the BR-2 152 mm corps-level gun was also unrealistic at that time. Whether the GAU liked it or not, therefore, the only option at the time was to develop a bunker buster based on the KV-7. In addition, although the ML-20 152 mm gun-howitzer proposed as the weapon for the new bunker buster was one-third shorter than the BR-2, it was still a very formidable weapon.