- Sketches and technical project, costing 100,000 rubles.
- Working blueprints, costing 200,000 rubles.
- Armoured hull produced at the Izhor factory, costing 150,000 rubles.
Work on a self propelled high caliber howitzer had to be put on hold, but the artillery officers never forgot about it. Eventually, the Artillery Committee ordered it back up and running. Item #12 on a list of projects at the Kirov factory (CAMD RF 38-11369-91) contains the following:
"203 mm self propelled B-4 howitzer on the chassis of a KV-1S tank. Kirov Factory and factory #172. Planned work for the Artillery Committee.
The Artillery Committee planning session from April 15th, 1942, identified the need for a self propelled Br-2 gun on the KV chassis. As a result of experience in the construction of self-propelled guns in 1942-1943, it was deemed possible to install a B-4 howitzer in a semi-enclosed SPG. The Kirov factory and factory #172
have a contract with Artkom's 16th department regarding this project. Each factory is developing the project separately."
The need for a Br-2 on a KV chassis appears even earlier, in a document from November of 1941 that lists SPG projects for 1942 (CAMD RF 81-12104-115).
In November of 1943, the GAU chief, Colonel Yakovlev, wrote a letter to the People's Commissar of Tank Manufacturing Malyshev:
"According to your announcement, the Commissariat of Tank Manufacturing intends to continue work on design and production of experimental self propelled 152 mm Br-2 and 203 mm B-4 guns, which was ordered by the GAU in 1940, but was interrupted in 1941 due to the start of the war.
The GAU considers this work to be necessary. The blueprints for the guns and ammunition have been sent to the Kirov Factory SKB-2 by GAU on June 19th of this year.
Orders to deliver a 152 mm Br-2 gun and 203 mm B-4 howitzer to factory #100 have been given.
The technical requirements, revised based on experience of the war, are currently being completed at GAU and will be sent to you in the coming days."
CAMD RF 81-12063-1
That desire was fulfilled in less than a year, in the form of the S-51 self-propelled howitzer. Unlike the previous designs, where the gun was fully enclosed, the S-51 mounted it on a mostly open platform, with a shield in the front that could flip up to protect the crew from shrapnel and bullets.
"An Order of the State Committee of Defense
On the question: manufacturing a party of 203 mm self propelled howitzers B4-S51
The Red Army accepts the 203 mm B4-S51 howitzer, developed by TsAKB NKV, consisting of the 203 mm B-4 field howitzer model 1931 on a KV-1S tank chassis.
NKTP (comrade Malyshev) and GURT of the Red Army (comrade Sosenkov) must deliver 50 repaired KV-1S tanks to NKV, without the rotating turret, and with an intact suspension, engine (with less than 10% of its lifetime hours expended), transmission, and spare parts by the following dates:
- 25 units by August 10th
- 25 units by August 25th
- By August 20th: 20 self propelled howitzers
- By August 30th: 30 self propelled howitzers
- Caliber: 203.2 mm
- Muzzle velocity: 607 m/s
- Maximum chamber pressure: 2366 kg/cm^2
- Shell mass: 100 kg
- Muzzle energy: 1900 ton-meters
- Maximum range: 18025 meters
- Vertical range: 0-60 degrees
- Horizontal range: +/- 4 degrees
- Ammunition capacity: 12 rounds
- Rate of fire: 1-1.5 RPM
- Full combat weight (according to TsAKB data): 49.7 tons
- Crew: 10
- Maximum speed: 30 kph
- Bore axis height: 2793 mm
- Recoil length:
- Long (up to 16 degrees 30 minutes): 1200-1300 mm
- Short (from 16 degrees 30 minutes and up): 850-890 mm
- Initial pressure in return gear: 40+/-2 atmospheres."