27th Guards Separate Heavy Tank Reg., 21st Army, Vyborg, 1944 - The Iosif Stalin tank (or IS tank, named after the Soviet leader Joseph Stalin), was a heavy tank developed by the Soviet Union during World War II. The tanks in the series are also sometimes called JS or ?? tanks. The heavy tank was designed with thick armour to counter the German 88 mm guns, and sported a main gun that was capable of defeating the German Tiger and Panther tanks. It was mainly a breakthrough tank, firing a heavy high-explosive shell that was useful against entrenchments and bunkers. The IS-2 was put into service in April 1944, and was used as a spearhead in the Battle of Berlin by the Red Army in the final stage of the war.