The IS-4 Soviet heavy tank started development in 1943 and began production in 1946. Derived from the IS-2 heavy tank and part of the IS tank family (the 'IS' acronym is the anglicised initialism of Joseph Stalin - ??´??? ???´???, Iosif Stalin), the IS-4 featured a longer hull and increased armour. Development started with the purpose of improving upon the earlier IS-2 model and incorporating captured enemy technology. This created a blend of IS-2 features and unique features not found in other Soviet tanks.