The Red Army encountered German Sturmgeschutz assault guns for the first time in 1941. The advantages of assault guns were that they were less expensive to produce than tanks with rotating turrets and that a larger gun could be fitted onto the same chassis. The Soviet Union was struggling with raw material shortages which made assault guns an attractive proposition.
Trench mortars made their first appearance in the Russo-Japanese war and were subsequently used by all belligerents in the First World War. It was found that the new, deadlier battlefield now demanded that all infantry troops be assisted by support weapons.