Soviet firing tests against a captured Tiger I heavy tank in April 1943 showed that the T-34's 76 mm gun could not penetrate the front of the Tiger I at all, and the side only at very close range. A Soviet 85 mm anti-aircraft gun, the M1939 (52-K), was found capable of doing the job, and so derivatives of it were developed for tanks. One of the resulting guns used on the original T-34 85 model (the D-5T) was capable of penetrating the Tiger I's upper hull armour at 1,000 metres.