KV series of tanks were named after Klementi Voroshilov, the minister of defence in the Soviet Union during the Second World War. The KV-1 was first used in the Russo-Finnish War in 1939. Armed with a 76.2mm gun of 30 calibers in length, weighed 46 tons, had a crew of five men, and was propelled by a 550hp diesel engine. Its frontal armour was 77mm and made the KV-1 resistant to most anti-tank weapons.
An improved model, KV-1A, that had a longer (40 calibers) 76mm gun, was introduced in 1940. The following year the KV-1B was developed and was given additional armour at the front and sides to give a thickness of 100mm.
The German Army found it difficult to cope with the KV tank during Operation Barbarossa. Even so, the Soviets continued to improve the vehicle and in 1942 the KV-1C was introduced. It had a new 600hp engine and its armour was now 130mm thick. The tracks were made wider to give better performances in mud and snow.