The Russian designation "SU", meaning Samokhodnaya Ustanovka or self-propelled gun, is a rather diffuse term that was equally applied to vehicles which in combat fulfilled the roles of dedicated tank destroyers, infantry-supporting assault guns, and even indirect-fire artillery, i.e. self-propelled howitzers. The SU-101/SU-102 as a replacement for the SU-100, which was mainly used as tank destroyer, was potentially intended to fulfill the latter's role. The 100 mm D-10S of the SU-101 was a dedicated tank gun with capable kinetic energy armour-piercing rounds. The 122 mm D-25S of the SU-102 against that had originally been developed as an artillery howitzer to be used with high explosive rounds. However, in the course of the war, the gun had also proved to be a very effective anti-tank weapon, capable of knocking out even heavy German tanks, and armour-piercing kinetic energy ammunition had been developed to augment this battlefield role. As such the gun was already in use with the heavier ISU-122 tank destroyer.