"Installation of a 203 mm mod. 1931 howitzer (B-4) on a KV-1S chassis (factory index S-51)
Produced by NKV TsAKB by order of the GAU Artkom.
The self propelled S-51 howitzer consists of the oscillating part of the 203 mm mod. 1931 howitzer (B-4) installed on a KV-1S. The installation is done in the following way:
The turret and turret ring are removed from the KV-1S. Instead of the turret, a plate is installed above the driver's head and the 203 mm mod. 1931 howitzer (B-4) is installed on it.
The fighting compartment remains free and is used to house the recoiling parts of the howitzer at high gun elevations.
Main characteristics of the experimental prototype:
Produced by NKV TsAKB by order of the GAU Artkom.
The self propelled S-51 howitzer consists of the oscillating part of the 203 mm mod. 1931 howitzer (B-4) installed on a KV-1S. The installation is done in the following way:
The turret and turret ring are removed from the KV-1S. Instead of the turret, a plate is installed above the driver's head and the 203 mm mod. 1931 howitzer (B-4) is installed on it.
The fighting compartment remains free and is used to house the recoiling parts of the howitzer at high gun elevations.
Main characteristics of the experimental prototype:
- Combat weight (by TsAKB data): about 50 tons
- Gun caliber: 203.2 mm
- Shell mass: 100 kg
- Muzzle velocity: 607 m/s
- Recoil resistance: 74,000 kg
- Vertical range: 0-60°
- Horizontal range: +/-4°
- Rate of fire: one shot every 1.5 minutes
- Crew: 10
- Ammunition carried: 12 rounds
- Top speed: 30 kph
- Total height with gun at 0°: 3400 mm
An experimental prototype of the self propelled S-51 howitzer underwent trials at the Gorohovets proving grounds from March 7th to April 6th of this year.
Trials were performed in the following amounts:
- 269 shots, 135 of them with increased charge.
- 524 km march, 76 of them across a stone road and off-road.
According to the proving grounds commission, the self propelled howitzer completed the trails successfully.
The following drawbacks were discovered during the trials:
- Significant movement of the entire vehicle backwards, especially at low elevations (up to 1300 mm).
- Significant jumping during firing (the front raised up by 250-450 mm, the rear sinks by 200-300 mm).
- Large sideways dispersion of the shells caused by the gun moving during firing.
Reducing the displacement of the vehicle, reduction of jumping, and better precision could be achieved by adding special trails, as it was done on the SU-14 self propelled gun designed at the Kirov factory in 1936. - During mobility trials, there was one case of the right final drive breaking down, one case of the right brake lining breaking down (overheated), and a series of other defects. This can be explained by poor condition of the vehicle used (the vehicle underwent major repairs and traveled 39.7 hours and 150 km since. The transmission and suspension were not repaired).
Installation of a 152 mm Br-2 gun on a KV-1S tank chassis
Produced by TsAKB on their own initiative.
The 152 mm Br-2 SPG does not differ in design from the B-4 SPG.
Main characteristics of the experimental prototype:
- Combat weight: about 50.5-51 tons
- Gun caliber: 152.4 mm
- Shell mass: 49.0 kg
- Muzzle velocity: 880 m/s
- Recoil resistance: no data
- Vertical range: no data
- Horizontal range: about +/-4°
- Rate of fire: no data
- Crew: 10
- Ammunition carried: 15-20 rounds
- Top speed: 30 kph
An experimental prototype of this SPG began factory trials at the Sofrino artillery proving grounds on May 20th of this year."