In the early years of the war, Soviet tanks like the T-34 and KV-1 could handle German armor. That changed in late 1942 when the Tiger tank appeared on the battlefield. Its thick armor resisted the 76.2 mm guns used by Soviet tanks, and reports of the Panther, then in development, made it clear that a more powerful weapon was needed. In May 1943, Soviet engineers began adapting the 85 mm anti-aircraft gun into an anti-tank weapon. Fyodor Petrov’s team produced the D-5 gun, which was too large for the turrets of existing tanks but could fit into a modified self-propelled chassis. The SU-122 assault gun provided the basis, and by replacing its 122 mm howitzer with the D-5T high-velocity gun, the SU-85 was born. The design entered production at Uralmash, with refinements such as a telescopic sight and a commander’s cupola added in later versions. The SU-85 kept the same mobility as the T-34 and had a low silhouette, which made it harder to hit. Its 85 mm gun could penetrate the Tiger I’s armor at about 1,000 meters, giving Soviet crews a much-needed tool against heavier German tanks. The first SU-85s reached the front in August 1943, in time for battles that followed the German defeat at Kursk. Crews valued its firepower, but as German tank designs advanced further, the weapon’s limits became clear. By spring 1944, the T-34-85 had entered mass production, combining the same caliber gun with the protection and versatility of a medium tank. This made the SU-85 redundant, and production ended later that year after about 2,650 units. A transitional model, the SU-85M, used the newer SU-100 chassis but retained the 85 mm gun until ammunition for the 100 mm D-10S became widely available. The SU-85 served across the Eastern Front until the war’s end, after which it was quickly phased out of Soviet service in favor of more powerful designs. Many vehicles were exported to allies and client states, including North Korea and Vietnam, where they remained in use for decades. Some were adapted into command and recovery vehicles, giving the design a second life even after its frontline role had ended.