When the Germans invaded the Soviet Union in June 1941 there were no self propelled guns in the Russian Army. The Soviets were impressed with all the self propelled guns that the Germans were using.
In 1942 the Defense Ministry decided to produced mobile artillery guns to support infantry and armored formations.1 The Zavod Nr 38 design team were given the specifications to design a self propelled gun.1 Initially, they were going to use the T-60 chassis to build upon.1 This chassis was found to be too small for the gun, so it was decided to use the T-70 chassis as it was stronger.1,5,6
The engine, fuel tanks, and driving positions were changed and moved to the right front. Some had rear doors and other open backs. Some had the radiators on the track covers and others in the engine compartment.
The driver was located in front of the main fighting compartment and had a passageway that connected him to the rear.2
Early models had an engine placed on each side of the vehicle.2 This lead to many breakdowns as it was a complicated setup.2
Late models had 2 GAZ 203 air cooled gasoline engines mounted in a row.2
|76.2 mm ZIS-3 (1942 model)2
||49 - 62 mm2
Captured Tanks Used
A design by a team from the Zavod Nr 592 to mount a 122 mm gun on a PzKpfw III chassis wasn't successful.1 Later, there were approximately 300 PzKpfw IIIs and StuGs captured at Stalingrad and it was decided to bring back that basic design, but with a 76.2 mm S-1 gun instead.1 These became the SU-76i (inostrannaya, "foreign").1