The Kliment Voroshilov (KV) tank

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The Kliment Voroshilov (KV) tanks were a series of Soviet heavy tanks named after the Soviet defence commissar and politician Kliment Voroshilov and used by the Red Army during World War II. The KV series were known for their heavy armour protection during the early part of the war, especially during the first year of the German invasion of the Soviet Union. In certain situations, even a single KV-1 or KV-2 supported by infantry was capable of halting large German formations. German tanks at that time were rarely used in KV encounters as their armament was too poor to deal with the "Russischer Koloss" – "Russian Colossus".

The KV tanks were practically immune to the 3.7 cm KwK 36 and howitzer-like, short barreled 7.5 cm KwK 37 guns mounted, respectively, on the early Panzer III and Panzer IV tanks fielded by the invading Germanforces. Until more effective guns were developed by the Germans, the KV-1 was invulnerable to almost any German weapon except the 8.8 cm Flak gun.

Prior to Operation Barbarossa, about 500 of the over 22,000 tanks then in Soviet service were of the KV-1 type. As the war progressed, it became evident that there was little sense in producing the expensive KV tanks, as the T-34 medium tank performed better (or at least equally well) in all practical respects. In fact the only advantage it had over the T-34/76 was its larger and roomier three-man turret. Later in the war, the KV series became a base for the development of the IS (Iosif Stalin) series of tanks.
https://en.wikipedia.org/wiki/Kliment_Voroshilov_tank