On June 22, 1942, Nazi Germany launched a blitzkrieg attack on the Soviet Russian, which started Russo-German War (known as the Great Patriotic War) during World War II.
Battle of Stalingrad became the turning point of World War II , the Russian began to turn to strategic counteroffensive, until the summer of 1943 broke out battle of tanks in kursk area. As this time the Soviet Union urgently needed more powerful tank to wishstand with Nazi’s division, so the Russian Central Design Bureau immediately adopted the KV-1S chassis, installation of new turret, this transition model is KV-85 heavy tank, as soon as possible in order to deploy heavy tanks to the front, Joseph Yakovlevich Kotin led the Central Design Bureau for KV-85 improved firepower , after some testing, and ultimately used with 122mm / D-25T gun, which is a prototype heavy tank KV-122, but not ratified this tank production, because the Soviets have developed another heavy tanks equipped with 122mm after the artillery program ---- is famous IS-2 heavy tank.