The SU-122 was the first self-propelled gun on the T-34 chassis to enter service with the Red Army. Originally developed to provide general close support for tanks and infantry, the SU-122 also proved to be an effective tank destroyer despite its unlikely armament. The 122mm M-1938 (M-30S) howitzer, with its relatively low muzzle velocity and lack of specialised armour-piercing ammunition, compensated for these shortcomings with the sheer weight of its projectile. However, it lacked appropriate tank-type direct fire sighting. The SU-122 was assembled at Uraltransmashzavod (UZTM) in Sverdlovsk, combining the chassis of the T-34 medium tank with the only armament then being produced in the immediate area. This wartime technical “marriage of convenience” utilised available resources around relocated manufacturing facilities and proved to be very successful.

The SU-122’s development was particularly nuanced. The journey to the SU-122 began with a series of turreted T-34-based tank destroyer designs that did not progress beyond the project stage. The first “series production” SU-122 was not built on a Soviet chassis at all; the early 122-SG was a combination of the 122mm M-30S howitzer with captured German StuG III and Pz.Kpfw. III chassis. A small number of these conversions were delivered to the Red Army. The first indigenous T-34-based SG-122M design aimed to re-arm combat-damaged T-34 tank chassis, but this concept was dropped due to a lack of donor vehicles. The final variant, based on newly built T-34 chassis, entered series production in December 1942 as the SU-35, later re-designated during production as the better-known SU-122. Although the SU-122 had a relatively short production life, it participated in most Red Army combat actions in 1943-44. It was eventually replaced in self-propelled artillery regiments by the SU-85, armed with an 85mm gun. A very small number of SU-122s survived to the end of the war, with some converted into ARVs serving for years beyond. The later and better-known SU-85 and SU-100 tank destroyers owe their origins to the SU-122 and the 1942 “marriage of convenience” in Sverdlovsk.