ZiS-2 (57 mm) M1943: Soviet anti-tank gun
In the beginning of 1940 the design office of Vassiliy Grabin received a task from the artillery department to develop a powerful anti-tank gun. The head of this department, Marshal Kulik, and his subordinates estimated that the use of heavily armoured tanks by the USSR in the Winter War (WW2) would not have gone unnoticed in Nazi Germany and would lead to the development of similar fighting machines there.
Therefore, Grabin and his office were guided by the characteristics of their own domestic heavy tank KV-1 with 40–75 mm armour. In the opinion of the designers the optimal calibre in this case was 57 mm. The velocity and mass of the armour-piercing 57 mm projectile allowed it to attain sufficient kinetic energy to penetrate up to 90 mm of RHA while keeping the gun sufficiently light, mobile and easy to conceal. However, the decision also had a downside: this calibre was a new one to the Red Army so the manufacturing of the projectile had to be started from scratch.
