I straight up took this from wikipedia, well still i was to lazy to type it all.The IS Tank was a series of heavy tanksdeveloped as a successor to the KV-series by the Soviet Union during World War II. The IS acronym is the anglicized initialism of Joseph Stalin (??´??? ???´???, Iosif Stalin). The heavy tanks were designed with thick armor to counter Germans 88 mm guns and carried a main gun capable of defeating Tiger II, Tiger I, and Panther tanks. They were mainly designed as breakthrough tanks, firing a heavy high-explosive shell that was useful against entrenchments and bunkers. The IS-2 went into service in April 1944 and was used as a spearhead by the Red Army in the final stage of the Battle of Berlin. The IS-3 served on the Chinese-Soviet border, the Soviet invasion of Hungary, the Prague Spring and on both sides of the Six-Day War. The series eventually culminated in the T-10 heavy tank.