The IS-2 is the early-generation second variant of the IS heavy tank family. With the arrival of the Panthers and Tiger Is on the German side, the escalation between German and Soviet engineers reached a new level, and the IS-2 was forced into service as soon as its primary armament was ready. The new heavy tank was the Soviet response to the increasingly superior German tanks, with a partially sloped hull front armour plate and a new enormous 122 mm D-25T tank gun. However, the IS-2 design would prove to have several flaws in the long term, beginning with the tank gun itself, which was difficult to reload and used heavy two-piece naval ammunition.