The KV heavy tank was designed and used a heavy break-through tank. To a tank of this task, the shortcomings of its L-11 main gun (which is not good at dealing with enemies" bunkers and forifications) could be fatal! So a heavy tank carrying a much bigger gun to better do the job was created along side the 76.2mm gun tanks. As such a big turret on the usual KV hull proved to be very un-maneuverable, it soon earned a funny nickname of "Mobile Washroom"! KV-1 Heavy Tank Designed to replace the disappointing multi-turreted T-35 heavy tank, the Soviet KV was in service from 1939 to 1945. The primary goal of the KV's designers was to build a tank with impenetrable armor, and they succeeded-any tank in service at the time of the KV's introduction would have had to attack at point blank range in order to breach its hull. It also had good firepower and traction, but was unfortunately slow and difficult to steer. By 1942, with the introduction of 50 and 75 mm guns and the high-velocity MK 10, the KV had lost its armor advantage, though it remained in service through the end of the war.