The SU-85 was a modification of the earlier SU-122 self-propelled howitzer, essentially replacing the 122 mm M-30S howitzer of the SU-122 with a D-5T high-velocity 85 mm antitank gun. The D-5T was capable of penetrating the Tiger I from 1000 m.[2] The vehicle had a low profile and excellent mobility. Initially given an armored commander's cap on the first batch, the SU-85's observational optics were improved by the introduction of a standard commander's cupola - the same as on the T-34/76 model 1942 - in addition to the already existing prismatic observation sights installed in left side and rear.