 Armour penetration of the armour-piercing (AP) rounds is reported as 37 millimetres of rolled homogeneous armour (RHA) at 60°at 500 metres range and 28 millimetres of RHA at 90° at 1,500 metres range.The naval mounting was produced as the 70K, and had entered service before the German invasion of the Soviet Union replacing the semi-automatic 45 mm/46 21-K on many ships.It was fitted in large numbers to Soviet ships during the Second World War, including the T301 class minesweeper.