The KV-13 program’s KV-85 prototype was accepted for production as the IS-1 heavy tank.

After testing with both 100mm and 122mm guns, the D-25T 122mm gun was selected as the main armament of the new tank, primarily because of its ready availability and the effect of its large high-explosive shell when attacking German fortifications.

The KV-122 replaced the KV-85, and began mass production as the IS-2.