This vehicle is a modification of the IS-2, developed from the early 1950s through the early 1960s. Before the T-10's development, the IS-2 was the main Soviet heavy tank. It remained in service until the mid 1990s. The tank chassis, power unit and turret were significantly changed. Some chassis components were adopted from the IS-3, as well as the splash shields and spare parts kit. The rear machine gun was removed from the turret. It was replaced with an additional fan for the fighting compartment. All gun embrasures were sealed. In addition, the standard engine was replaced with the V-54K-IS engine. The ammo capacity was increased to 34â??35 shells, while the standard gun (the 122 mm D-25) remained unchanged. However, the gun elevation mechanism was improved. Some vehicles were equipped with the TVN-2 night-vision devices. Besides this, the new R-113 radio was equipped instead of the standard one. In addition, the driver's observation devices were improved.