The North-Western Front HQ ordered first four KV tanks from experimental party to be armed with 152 mm howitzers. To do this, the best engineers from KTZ's design bureau were summoned. After two weeks a new project was completed. Initially, the engineers decided to use the 152 mm Howitzer Model 1909/1930, but later it was replaced with more modern 152 mm M-10 Howitzer Model 1938/1940. A new, larger turret was designed to accept such heavy cannon. That turret was named «MT-1».
At the beginning of 1941, the tank was renamed KV-2. The MT-1 turret was placed on the chassis of a twin-turret experimental tank instead of small turret (a large turret was also removed from the hull). On February 10, 1940, first trials were conducted. At the time, Soviet tank designers weren't too experienced in the heavyweight field. They added a small lid on the the howitzer barrel. That lid was intended to prevent a gun from the dust, shell fragments and bullets. However, after the first shot this lid was torn away and never used again.
In 1940, a pair of KV-2 were sent to the battlefront on the Karelian isthmus. Contrary to the rumors, KV-2s didn't take part in battles before the war with Germany. A pair of KV-2 fired at already captured pillboxes. The results of the tests were excellent and later the KV-2 heavy tank was accepted for service. Soviet soldiers often nicknamed it a «Dreadnought».
When production has already started, the turret was slightly improved and additional DT machine-gun was mounted in it. The shortened M-10 howitzer was able to fire a 52-kg high-explosive projectile with muzzle velocity of 436 m/s.
During WWII, most of KV-2 tanks were lost. For example, 41st Tank Division lost 22 KV-2 tanks (of 33 total). Only 5 tanks were destroyed by the enemy, other 17 were abandoned due to breakdowns or simply ran out of fuel.
In October 1941, the KV-2's manufacture was canceled. Totally 334 KV-2 tanks were produced.