IS Iosif Stalin Heavy Tank

The IS (Iosif Stalin) heavy tank in Russian sources is usually referred to as "Tank of the Victory". Development of the IS (Iosef Stalin) series of tanks, started in late 1942, began in earnest in 1943 as a response to the performance of the German Panther and Tiger tanks at the batttle of Kursk. The IS tanks were updated versions of the earlier KV with better mechanical reliability and more powerful weapons. The IS-2 (Iosef Stalin 2) was the first production version, weighing over 40 tons. The IS-2 heavy tank was equipped with external fuel tanks and a 122mm gun.
During 1944 further development efforts led to improvement in the the armor which later led to the IS-3. In contrast to previous designs, the main concern was to provide maximum protection against anti-tank projectiles. The IS-3's armor was made from rolled steel plates welded together and mounted at sharp angles, producing the signature pointed glacis. Another innovation was the semicircular aerodynamic cast turret. IS-3 had an improved fire control system allowing the tank's commander to traverse the turret thereby directing the gun faster.

The IS-2M tank was developed in 1951-1962, as a result of the IS-2 upgrade program. The modified IS-2m introduced a new, simpler and better angled bow casting.

The IS-2 and IS-3 were the primary Soviet heavy tanks in the immediate post-war years, but were eventually replaced by more modern models. IS-3 tanks remained in service with the Red Army until late 1960s. Some surviving for decades thereafter in the inventories of other countries, such as North Korea and China. They also served with Cuban and some Arab armies.