Background
Prior to the start of World War Two, the armed forces of the Soviet Union were lacking in any sort of self propelled artillery. Following the invasion of the Soviet Union by German forces in 1941, Soviet forces suffered massive loses of military material. Hand in hand with these losses came the forced uprooting of many of their key military production plants eastwards, away from the advancing German armies. But these plants were soon up and running again, and with heroic efforts on the part of the workers and plant managers, were soon churning out replacement vehicles in an attempt to cover the initial losses.