sentences:  Unlike other automatic guns employed during World War II the barrel of the 20 mm Oerlikon gun did not recoil, the breechblock never locked against the breech and actually moved forward when the gun fired.This weapon lacked a counter-recoil brake, as the force of the counter-recoil was checked by the explosion of the next round of ammunition.Between December 1941 and September 1944, 32% of all Japanese aircraft downed were credited to this weapon, with the high point being 48.3% for the second half of 1942.