The KV heavy tank was designed and used as 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 enemie bunkers and fortifications, 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. The first of this type uses a new big high turret of 7 sides that mounting the 152mm M-10 howitzer. This version, which had many detail differences to the later standard type was usually dubbed KV "Big Turret" or KV-2 Model 1939. 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".