The SU-122 (from Samokhodnaya Ustanovka 122 mm) was a Soviet self-propelled howitzer or assault gun used during World War II. The number "122" in the designation represents the caliber of the main armament, a 122 mm M-30S howitzer. The chassis was that of the T-34. Development history The Soviet High Command became interested in assault guns following the success of German Sturmgeschütz IIIs. Assault guns had some advantages over tanks with turrets. The lack of a turret made them cheaper to produce. They could be built with a larger fighting compartment and could be fitted with bigger and more powerful weapons on a given chassis. However, assault guns generally aim by orienting the entire vehicle, and were thus less suited for close combat than tanks with turrets. In April 1942, design bureaus were asked to develop several assault guns with various armament: 76.2 mm ZiS-3 divisional field guns and 122 mm M-30 howitzers for infantry support, and 152 mm ML-20 howitzers for attacking enemy strongholds. A prototype assault gun, armed with the 122 mm howitzer and built on the German Sturmgeschütz III chassis was developed, designated SG-122. Only 10 of these were completed. Production was halted when the vehicle was found to be hard to maintain and judged to be unsuccessful. Simultaneously, an SPG based on the T-34 medium tank was also developed. Initially, the T-34's chassis was selected for the 76.2 mm F-34 gun. This vehicle, the U-34, was created in the summer of 1942 at UZTM (Uralmashzavod – Uralsky Machine Building factory) design bureau, by N. W. Kurin and G. F. Ksjunin. It was a tank destroyer with the same armament as the T-34, but without a turret. The vehicle was 70 cm lower than a T-34, had thicker armor, and was 2 tonnes lighter. It did not enter production. UZTM then worked on combining features of the U-34 and the SG-122. Initial design work was completed between July and August 1942. The project emphasized minimizing modifications to the platform and the howitzer. It used the same chassis, superstructure, engine and transmission as the U-34 and was armed with (the then new) 122 mm M-30S howitzer from F. F. Petrov's design bureau. This vehicle also used the same gun bed cover and mountings as the SG-122, to keep costs low and simplify production. It had 45 mm thick frontal armor. The M-30S howitzer could be elevated or depressed