107mm ZiS-6 guns, initially designed for use on KV-4 and KV-5 tanks, were for testing purposes mounted on KV-2 turret to learn how the guns will operate in the field. however, as the projects for super-heavy tanks were canceled, about 600 produced ZiS-6 guns were destroyed.
KV-2 with 107mm ZiS-6 gun was only one example of the tank to test the guns for heavier tanks. By World of Tanks game, this configuration would have made KV-2 very dangerous tank, with good rate of fire and penetration power. however, KV-2 with this gun never seen active service.