Development of KV-220 on the basis of the KV heavy tank started in the summer of 1940. A prototype was built on December 5. Unlike other KV modifications, the tank featured an elongated hull, additional support roller, enhanced armor (100 mm), and a new turret with the 85 mm F-30 gun. In the fall of 1941, production of the KV-1 was discontinued. The vehicle received the mass-produced KV turret and was sent to the frontlines.