The combat experience of the initial period of the Great Patriotic War proved the need for self-propelled artillery to accompany tanks in battle, and in October 1942 the State Defense Committee decided to begin work on the creation of a self-propelled artillery vehicle (SPG) based on the T-34 tank with a 122 mm M-30 howitzer of the 1938 model, which was adopted by the Red Army in December (!). Of course, the hastily created vehicle was not without its shortcomings, which had to be corrected right at the start of mass production. The resulting self-propelled gun, which had the factory designation U-35 (SU-35) and the army designation SU-122, went into mass production at the Ural Heavy Engineering Plant (UZTM) at Sverdlovsk. Throughout the entire period of serial production of the SU-122, which lasted from December 1942 to August 1943, there was a continuous improvement in the quality and manufacturability of its production: the work carried out to improve the production and assembly technology made it possible to significantly reduce the labor costs for the production of the machine.

Structurally, the SU-122 was a hull of the T-34-76 tank with the control and fighting compartments combined in a casemate. This compartment housed weapons, seats for the driver, commander, gunner, and two loaders, ammunition, controls, control instruments and a radio station. The commander also served as the radio operator and air guard. On the roof of the cabin was a cupola with three inspection ports for a periscope sight and a hatch.

The engine and transmission compartments, as well as the chassis, were unchanged from the T-34.

This self-propelled gun was armed with a 122 mm M-30S howitzer. The pinned upper carriage of the 122 mm field howitzer of the 1938 model was placed in the socket of a special cabinet mounted in the front part of the hull bottom. The swinging part of the howitzer was attached to the axles of the machine, and the barrel, cradle, recoil devices, sight and guidance mechanisms were taken over as standard without any changes. The need to armor the swinging part made it necessary to strengthen the spring balance mechanism, which was done without changing its dimensions. The direct firing range of the gun was 3600 m, and the maximum indirect firing range was 8.0 km. The shells used were mainly high-explosive separate charges OF-462 weighing 21.76 kg (with an initial velocity of up to 515 m/s). Against tanks, cumulative projectiles of the BP-460A type (13.34 kg, 335 m/s, armor penetration 120 mm) could be used.

In total, UZTM built 638 SU-122s. Self-propelled guns of this type were delivered to self-propelled regiments (a mix of SU-76s and SU-122s), and from April 1943 — to medium self-propelled regiments (SU-122 only). The regiments were supposed to be attached to tank and mechanized corps but were often used in support of the infantry.

SU-122s took part in the Battle of Kursk. Together with the heavy SU-152s, they proved to be one of the few combat vehicles that could withstand German innovations, so from the second half of 1943, SU-122s were often used as antitank weapons. At the beginning of 1944, they were replaced by new self-propelled guns of the SU-85 type, better suited for fighting tanks, but the SU-122 continued to be used in the regiments where they were retained. It is interesting that at the same time, the commanders tried not to send them for repairs (otherwise they would be replaced by SU-85s), but to repair them on the spot, so that a certain number of SU-122s even reached Berlin.

Used sources:

1. M. Baryatinsky “Self-propelled guns based on the T-34 tank,” magazine “Armor Collection” No. 01 2000

2. M. Svirin “Stalin’s self-propelled guns. History of Soviet self-propelled guns 1919-1945" 2008

3. G.L. Kholyavsky "Complete encyclopedia of tanks of the world 1915 - 2000" 1999