Based on your analysis, please advise which tank we should to settle on and issue an order to have drawings of that tank’s hull sent to Factory No. 92; we have drawings of the T-34.{1}
Unfortunately, we still do not know what 400 mm mortar was planned for mounting on a KV-1S or T-34 chassis. Nothing is known about the development of such systems by Factory No. 92. Yelyan received an answer to his letter on December 14:
Operation of KV tanks has shown that the running gear and engine of the 50-tonne tank are under a heavy load and frequently break down. This led to the development of the lighter KV-1S tank, which weighs 42.5 tonnes.
The power of the KV-1S engine, its location, and the strength of its suspension and hull components differ little from those of the KV-1 tank.
We cannot say whether the tank’s suspension would hold up under a 100-tonne load because we have no experience with use of the system under such loads.
Without knowing the design characteristics of the mortar, we can draw no conclusions about the feasibility of installing it in the tank.{2}
The idea of an open SP gun based on the KV-1S surfaced again in the spring of 1943. Paragraph 12 of a report on the state of SP artillery manufacturing and developmental efforts prepared by the GAU’s Artillery Committee addressed a “203 mm self-propelled howitzer on a KV-1S tank chassis.” The report was dated April 28, 1943:
The April 15, 1942, resolution of a plenary session of the Artillery Committee proposed development of an engineering design for a BR-2 self-propelled gun on a chassis incorporating assemblies from the KV tank.
Experience gained in building vehicles between 1942 in 1943 has shown that a B-4 howitzer can be mounted on a KV-1S chassis in the form of a semi-enclosed vehicle.
By agreement with the 16th Department of the Artillery Committee, the Kirov Factory and Factory No. 172 are developing this project. Each factory is working independently.{3}
There is almost no information about the Kirov Factory design. According to the correspondence, drawings of the rounds and traversing mechanisms of the B-4 and BR-2 guns were sent to SKB-2 on June 19, 1943. Work ceased at that point. No information about this project exists in SKB-2’s experimental work. Publications by some Russian authors mention similar efforts at the Ural Heavy Machinery Plant, but they found nothing like that among the Sverdlovsk projects. These projects may have involved mounting the BR-2 and U-3 in the SU-152, but these are SP assault guns, not open vehicles.
As far as Factory No. 172 is concerned, its design bureau developed the M-17 heavy SP assault gun with the M-40 203 mm howitzer, which clearly was not what the GAU’s Artillery Committee was asking for. As discussed above, instead of the M-17 the GAU’s Artillery Committee and the Technical Council of the People’s Commissariat of Arms required Factory No. 172 to develop a design for an open SP gun chassis armed with the B-4 203 mm heavy howitzer. Despite the fact that the task was issued in July 1943, there was no activity on that project in either August or September. In early September, the Central Artillery Design Bureau was added to the heavy SP gun program, and some of the designers who had proposed a similar SP gun less than a year previously were transferred to it.
It is worth noting that, in addition to the KV-1S chassis, the TsAKB was also considering other platforms for mounting the BR-2 and BR-4. A September 8, 1943, letter discussed transferring to the design bureau materials for SP gun projects based on the T-34 that Factory No. 221 had developed in early 1942. The BR-33P and BR-33G were then scrapped as not conforming to the specifications for bunker busters. That is absurd because the wording of the specifications changed radically a year and a half later:
The TsAKB of the People’s Commissariat of Arms has appealed to the GAU’s Artillery Committee with a request for materials in the Artillery Committee’s files on the 203 mm and 152 mm SP guns developed by Factory No. 221.
In early 1942, Factory No. 221 submitted projects for 152 mm and 203 mm self-propelled guns on chassis incorporating T-34 tank assemblies for a finding by the Artillery Committee.
The Artillery Committee approved these projects, but the situation at the time prevented them from being implemented.
In the belief that it is desirable and timely to begin developing new heavy self-propelled guns, and as one version of a plan prepared by Factory No. 221, which the Artillery Committee currently approves, I hereby request that the appropriate task for completion of this project be issued to TsAKB of the People’s Commissariat of Arms.{4}
On September 15, 1943, when the decision was made to continue work on tank, towed, and self-propelled artillery, the TsAKB was the only bureau working on SP guns mounting the B-4 and BR-2. According to documentation, the project was not a high priority. Nevertheless, on October 8 People’s Commissar of Arms Ustinov reported to Beria on the status of the Central Artillery Design Bureau’s new SP gun projects:
The Central Artillery Design Bureau (TsAKB) of the People’s Commissariat of Arms for lightly armored, semi-open vehicles for the BR-2 152 mm gun and the B-4 203 mm howitzer, as well as a closed assault vehicle for a 152 mm gun with the ballistics of the BR-2 and a 203 mm howitzer with the ballistics of the B-4.
For the TsAKB to manufacture prototypes of the vehicles, it needs to obtain from the People’s Commissariat of the Tank Industry two KV-1S or IS tanks without guns and turrets, one SU-152 chassis without its gun, and drawings, including general view drawings, of the KV-1S and IS tanks and the SU-152 vehicle.
I hereby request that the People’s Commissar of the Tank Industry (Comrade Malyshev) be instructed to act accordingly.{5}
An unexpected competitor to the TsAKB project emerged just a few days later. On October 15, a letter forwarding the engineering design for the M22 SP gun was sent to the Technical Council of the People’s Commissariat of Arms, the GAU’s Artillery Committee, and the GABTU. Judging by the dates on the drawings, this SP gun had been developed in early October under the leadership of V. A. Ilyin, chief of Factory No. 172’s artillery design bureau. Despite the fact that this project was not recorded in the factory’s plans, the M22 was not his own initiative, as is evident from a memorandum:
Based on GAU Artillery Committee letter No. 829360s and People’s Commissariat of Arms letter No. 1888s, dated August 28, the Design Bureau of Factory No. 172 has developed and hereby submits the conceptual design for the M22 203 mm self-propelled howitzer.