The Sturmgeschütz (StuG), meaning “assault gun”, was used during WWII as an ASPIS (Armored Self-Propelled Infantry Support). The main versions used were the StuG III and StuG IV. They were good at destroying bunkers, pillboxes and other entrenched positions. After the USSR developed the T-34, they had to fit the StuGs with 75mm Pak 40s instead of the 37mm guns. The StuGs with the new guns proved effective as tank destroyers as well.