KV1 tanks, named after soviet defence commissar and politican Kliment Voroshilov, were soviet heavy tanks used in WW2.
Production of this tank started in 1939. At that time, there was no match for this tank. Yes, he was slow, and had some mechanical problems, but huge advantage was his great armor.
German tanks, Panzer III and Panzer IV with 3.7cm KwK 36 and 7.5cm KwK 37 could not penetrate KV1.
Main armament of this tank wa 76mm L11 gun, with 7.62mm DT machine gun on rear side of turret.
There were many variants of this tank like KV-1A, KV-1B, KV-1C, KV-1S, KV-85, KV-2 and also this tank was base for developmetn of IS heavy tank.
KV-2