After the successful tests of the 107mm ZiS-6 cannon on the KV-2, several new heavy and super-heavy tanks were designed around it. The KV-3 was the first of such designs to be built, but the 107mm was not a requirement for it. Three designs were submitted for the KV-3 project, all based on the long chassis of Object 220: Objects 221, 222, and 223. The latter was chosen, using a sloped, elliptical turret with commander’s cuppola and armed with the 107mm cannon. A single prototype each of both Object 220 and Object 223 were constructed in 1941, but destroyed when the Wehrmacht attacked Leningrad.
Object 150 (T-150)
Object 220 (KV-220)