The COW 37mm gun was an early large caliber aircraft weapon trialled by the British in WW1. It was tried unsuccessfully in several aircraft and in mountings on the ground.
The 37mm Nose Cannon appear in Battlefield 1 as an ammunition type available for Attack Planes with the Tank Hunter Aircraft Package. The 37mm Nose Cannon fires one shot at a time which causes significant recoil to the aircraft firing. Additionally, the cannon has significant drop which must be accounted for. That being said, the 37mm Cannon does much more damage to tanks than any other weapon available for the attack plane.