Experimental versions of the cannon were produced, including some with a magazine or belt feed for the ammunition.

Later trials were at an Army range at Manorbier of a gun mounted on a 30 cwt[clarification needed] Morris truck (which by a fluke hit a target plane on its fourth shot) and at the Royal Navy's waterborne trials off Whale Island.

[4] Although the Rolls-Royce 40 mm cannon was never deployed in aircraft, with the Fall of France in 1940 the Royal Navy found itself lacking armament in its coastal craft to respond to German E-boats.

[5] The first sea trials of the cannon were undertaken in September 1940 and it entered service in 1941 after teething troubles were ironed out.

[6] Over 600 40 mm cannon were manufactured under sub-contract by British United Shoe Machinery (BUSM) in Leicester, since Rolls-Royce was forbidden by Lord Beaverbrook, the Minister of Aircraft Production, to tie up resources on them.