equipped with a long-barreled 76.2 mm gun ZIS-5 that can penetrate the armor of the German tank
active in Operation Barbarossa (Axis invasion of the Soviet Union), in June, 1941
KV-1 Model 1939 - First production models used in Winter War (First Soviet-Finnish War, 30 Nov 1939 – 13 Mar 1940), armed with 76 mm L-11 tank gun usually with no hull machine gun, early production had cast turret (different from one used on 1941/42 models). 141 were built.
KV-1 Model 1940 (KV-1A) - armed with 76 mm F-32 gun and a new mantlet. The main production model by the time of the German invasion.
KV-1 Model 1940 s ekranami (KV-1E) - with additional bolted-on appliqué armour and armed with 76 mm F-32 gun.
KV-1 Model 1941 (KV-1B) - armed with long-barreled 76.2 mm ZIS-5 tank gun. Up-armoured with 25–35 mm added to the turret, hull front and sides. Later production had cast turret.
KV-1 Model 1942 (KV-1C) - fully cast turret with thicker armour, using an improved engine and 76 mm ZiS-5 tank gun.
KV-1S - thin armour & high speed version, with a new & smaller cast turret. 1370 were built.