KV-3, Object 223 - Experimental tank based on KV-1. Longer chassis (7 rollers per side). New 850 hp V-2SN engine. 130 mm armor. New conic turret. 107mm ZiS-6 cannon. One prototype was constructed and proved in 1941, and mass production was planned to begin the same year. The German invasion halted these plans. Subsequently, the sole prototype was destroyed in battle against German heavy guns.