The KV-2 was a largely experimental heavy artillery tank that made use of the 152,4mm M-10 howitzer in a tall turret on a KV-1 chassis. The larger turret with thicker armour added a full ten tonnes to a vehicle that was already too heavy for its outdated transmission, resulting in a tank that, although powerful and intimidating, was extremely unreliable. Much like the KV-1, the KV-2 was immune to all German guns smaller than the 88mm, and if it took advantage of a hull-down position, even that couldn’t damage it at long ranges. The KV-2 was eventually used as a test-bed for the 107mm ZiS-6 cannon, which had a higher muzzle velocity and much longer range than the 76,2mm cannon employed on the KV-1. These tests led to the development of even larger vehicles.
U-3, sometimes (erroneously) called KV-2 M1939