In March of 1942, the Separate Design Group organized by the NKV Technical Council in order to work on self propelled guns designed an SPG consisting of a mod. 1938 122 mm howitzer on top of a captured German StuG. This project, indexed SG-122, was approved by the Technical Council and Artkom.
An Artkom plenum that was examining issues of self propelled guns in early April of this year also remarked that it is necessary to rapidly begin production of the SG-122.
The People's Commissar of Armament, comrade Ustinov, signed order #217s to organize the production of experimental prototypes at factory #592 and the creation of a special design bureau.
Specifics of the self propelled SG-122 gun
- High firepower: The 122 mm shell and its HE action combined with sufficiently high muzzle velocity (512 m/s) and high rate of fire (10-12 RPM) make the SG-122 a powerful weapon against enemy pillboxes, field fortifications, machinegun nests, and other fortifications.
- Protection: The use of an armoured casemate results in less casualties compared to towed artillery.
- Mobility: It is possible to follow tank units and open fire at fortifications from a short range in order to destroy them and clear the path for tanks.
- Versatility and agility: The SPG can fire when stationary and on the move, quickly shift fire, turn on its tracks, and aim approximately using a simple aiming device for the driver (made of two planks). Variable propellant loads and high angles of elevation make indirect fire possible, making it possible to destroy closed or far away targets, as well as hull down targets.
- Stability: The mass of the SPG is sufficient to fire without deploying trails.
- Maneuverability: The small increase in mass (2 tons) does not reduce maneuverability characteristics.
- Protection of the crew from fumes: When shooting at a high rate of fire, gas masks can be worn, connected with extended hoses to the outside air, bypassing chemical filters, which can be switched on in case of a gas attack. Trials show that wearing gas masks has almost no impact on the rate of fire. If the hatches are open or the engine is running, it is possible to fire quickly without gas masks.
- Use of 9-R Radios and PTU-4 bis.