 By 1942, the 76.2mm F-34 tank gun of the T-34 medium tank was found to be lacking in range and penetration compared to the German 75 mm Pak 40 anti-tank gun, new mounted on the Stug III and Panzer IV, and markedly inferior to the 88-mm gun of the Tiger I.Military planners directed the design bureaus of both Gen. Vasiliy Grabin and Gen. Fyodor Petrov to modify the 85mm anti-aircraft gun for use as an anti-tank weapon.Petrov's bureau developed the D-5 85mm gun.