"The special NKV telegram #5014 sent on September 24th, 1943, tasked OKB-172 and the #172 Molotov factory to develop a 122 mm self propelled gun, capable of reaching 1000 m/s muzzle velocity with a 25 kg shell.
Giving the highest priority to this project, OKB-172 completed the draft ahead of schedule, and presents it for your approval. As a result of performing the draft work, we have discovered the following:
- The task of creating an SPG with the muzzle velocity of 1000 m/s can be accomplished by installing a new barrel on the KV-14 SPG, to replace the model 1937 howitzer, and a new single-sided hydro-pneumatic balancing mechanism.
- As the power of cannons constantly grows, you may be interested in our installation of an OBM-43 barrel, with the muzzle velocity of 880 m/s and a 43.5 kg shell, on the KV-14 SPG, instead of the 122 mm barrel with the 1000 m/s muzzle velocity. Such a solution raises the power of the SPG by 33.5% and increases its armour piercing and concrete piercing capability.
- 1000 m/s muzzle velocity
- 200 mm of penetration at 1000 meters
- Use of existing A-19 shells
- Maximum compatibility with ML-20S components
"As ordered by the Tech-department of the NKV, OKB-172 developed a project for a modernization of the KV tank by installing a 122 mm gun. The modernization removes the current KV turret and all its armament, and replaces it with a new turret that holds a 122 mm high power gun, two machine guns, and the ammunition rack. The rest of the tank, all of its mechanisms, components, and armoured hull, including the turret ring, remain the same.
The 122 mm gun designed by OKB-172 has the following characteristics:
- Caliber: 122 mm
- Muzzle velocity: 950 m/s
- Shell mass: 25 kg
- Maximum gas pressure: 2660 kg/cm^2
- Barrel length with muzzle brake: 58.5 calibers
- Recoil resistance: 16 tons
- The modernization of the KV tank to equip it with a powerful 122 mm gun is a modern and reasonable course of action.
- The project is approved to continue to the prototype stage.
- It is reasonable to also adapt the modernization project, including the turret, to the IS tank.
- During development, it is suggested to:
- Use the D-5 mount, as it is the most compact.
- Use a horizontal sliding breech.
- Increase the muzzle velocity to 1000 m/s on the IS chassis.
- Develop a cast turret variant, and make it as short as possible.
- Reduce the ammunition capacity to 30 shells to reduce turret height and mass.
- Allow for shooting on the move, move the fire button to the elevation mechanism. Implement a secondary electric fire mechanism.
- Reduce the tank mass to 45 tons.
- Give OKB-172 the highest priority, given the importance of this project.
- Suggest that OKB-172 work with naval armament factories."