KV-1 The KV series was a production line for a series of heavy main battle tanks of Soviet origin. They were named after defense commissar and politic...ian Kliment Voroshilov. At the time of Germany's invasion of the Soviet Union in World War II, KVs were the best-protected main battle tanks of their time, but they only made up 2%1 of the total Soviet armored forces in 22 June 1941. His initial success in stopping and decimating "panzer" forces earned him the nickname "Nazi killers."