A prototype of the KV-II was completed in November, 1939, by which time that of the KV-I had already appeared, and immediately put to tests. As a result, it proved to have a serious disadvantage because its turret was too heavy, weighing several tons. The turret did not revolve well when the tank was on slopes whether it was running or not. It was unfortunate for the KV-II that the Soviet-Finnish War broke out that month. The Russian military authorities regarded the KV-II as the tank best suited for attacking fortified positions. Thus the KV-II entered production without undergoing substantial improvements in the turret which did not always revolve well.

The correctness of the Russian military authorities judgement was proved by the fact that the KV-II contributed much to the sucessfull breakthrough of the Finnish Mannerheim Line on 16th February, 1940.