After receiving approval from the GKO, the first 25 SU-122 were completed still in December 1942.
SU-122's were used to form medium self-propelled artillery regiments.
These Medium SP regiments consisted of 16 SU-122's (organized in four batteries) and one commander's T-34 tank.
Soon, the new SU-122 became very popular due to it's quite powerful armament and good armor protection.
In May 1943, the new BP-460A HEAT (High Explosive Anti-Tank) round was accepted. That ammunition allowed the SU-122 to deal with enemy AFV's at long distances.
However, like with most Soviet self-propelled guns, its primary role was direct fire support ot infantry against enemy strongpoints.
Two attempts to improve the performance were undertaken at Uralmash, called »SU-122M« and »SU-122-3«.
The main improvement was the adoption of a new ball mount for the gun which improved its traverse and the vehicle's frontal protection.
The advent ot the more powerful »
SU-152« self-propelled gun as well as the highly effective »SU-85« tank destroyer, however, led to the decision in November 1943 to discontinue production of the SU-122 just 11 months after the first of 638 vehicles had been produced.