SU-85 production started in mid-1943, with the first vehicles reaching their units by August. When the up-gunned T-34-85 medium tank entered mass production in the spring of 1944, there was no point in continuing production of a tank destroyer without superior firepower.[4] In light of this, SU-85 production was stopped in late 1944 after 2,650 vehicles had been produced. It was replaced on the production lines by the SU-100 tank destroyer, armed with the more powerful 100 mm D-10S gun, but due to delays with 100 mm ammo, a stopgap version called SU-85M appeared in September 1944, which was SU-100 fitted with 85 mm gun, already with thicker frontal armor and commander's cupola.