The Rolls-Royce 40 mm Cannon was a project first proposed in late 1938 to produce a cannon for mounting in aircraft which could cause sufficient damage to bring down a large bomber. It was envisaged as a suitable weapon for destroying tanks from the air. Experimental versions of the cannon were produced, including some with a magazine or belt feed for the ammunition. Examples were fitted to a Bristol Beaufighter and Hawker Hurricane for testing, although never used in action. Development of the aircraft cannon to iron out problems came to an end in 1943 when the Air Ministry lost interest in it and had started to favor the RP-3 rocket projectile as its preferred aircraft anti-tank weapon.