KV-3 tanks with 120 mm frontal armor, 90 mm of side protection, this comprehensive protection even more powerful than nearly a year later the German Tiger tanks. Design requirements to improve the artillery power, so KV-3 selected Navy B-34 type 107 mm gun, and to improve to become the ZIS-6-type gun, the gun's muzzle velocity of 800 meters per second, firing armor-piercing time, UBR -420 type penetrator weighs nearly 19 kilograms, can penetrate 167 mm of armor at 500 meters. To improve the shooting angle, the gun in the turret angled shot no less than 30 degrees, while 92 factories and GKO factory started to design the transformation model, and after the completion of the transfer to the Kirov plant, and require the production of 500 in 42 years carrying 107 guns KV-3 tanks.