During WWII the Russians were very quick to notice the advantages of the German StuG series of assault guns. From a production point of view they were cheaper and simpler to build, and in the field they could be armed with larger calibre weapons than the gun tanks whose chassis they used. The major disadvantage was the limited traverse and elevation of the main armament and the need to manoeuvre the whole vehicle to counter any threat from the sides or rear. As the war progressed the Germans were forced to use StuGs in place of tanks for a variety of tasks; by contrast, with numerical supremacy of machines and men. the Russians had the luxury of using assault guns in their intended support role behind the tank led spearhead, accompanied by lank riding infantry offering protection to the flanks and rear. Based on the highly successful T34 chassis, the SU 100. armed with the 100 mm D10s. was developed to replace the SU85. which mounted the 85 mm D5-S-85. when this became the regular armament on the T34/85. A larger calibre gun was also necessary to counter the heavily armoured German Tiger when used in the antitank role.
