According to GOKO decree #3187ss issued on April 15th, 1943, and #3289ss, issued on May 5th, 1943, and orders of the People's Commissar of Tank Production and People's Commissar of Armament #233ss/260ss, issued on May 8th, 1943, Uralmash factory, factory #9, TsAKB, Kirov factory, and factory #8 were instructed to design and produce an 85 mm SPG.
TsAKB (comrade Grabin) was instructed to design the gun, factory #9 was instructed to build it, and Uralmash was instructed to build the hull and suspension.
During this project, the following guns were proposed for installation on the T-34 chassis:
- TsAKB: 85 mm S-18 gun.
- Uralmash: 85 mm S-18-1 gun, the TsAKB design with minor changes (welded mount).
- Factory #9, personal initiative: 85 mm D-5S-85 gun.
- Factory #9, personal initiative: 122 mm D-5S-122 howitzer, which has many parts in common with the D-5S-85.
- SU-85-I with the 85 mm S-18-1 gun (TsAKB project with Uralmash modifications)
- SU-85-II with the D-5S-85 gun (factory #9 project)
- SU-85-IV with the 85 mm S-18 gun (TsAKB project)
- SU-122-III with the 122 mm D-5S-122 howitzer (factory #9 project)
- All four vehicles passed mobility trials, but not gunnery trials.
- Considering that rapid adoption of an 85 mm gun by the Red Army is necessary, the commission considers the 85 mm SPG armed with the D-5S-85 gun designed by factory #9 and using the armoured self propelled chassis with a casemate that flares out above the entire width of the tracks.
- Factory #9 must make the necessary changes in the blueprints of the 85 mm D-5S-85 gun to correct defects of the gun and its mechanisms, established by the commission during trials and outlined in the "conclusions" section of the report."