English: Rolls-Royce type BH 40mm Aircraft Cannon (1942) on display at the Silk Mill Museum, Derby, in 2010. May not now be on display.

From the display captions: "As early as 1938 Hives [Ernest Hives, General Works Manager and a director of Rolls-Royce] was concerned about the lack of British made guns for aircraft. As a stimulus to the arms manufacturers a small armaments section was set up at Rolls-Royce in Derby. This developed a 40mm quick firing cannon." "Intended for tank busting aircraft such as the Hurricane IID, a small number were fitted to these aircraft in 1942, but never saw action due to a change in tactics and the development of rockets." "After the fall of France the Admiralty expressed an interest in using the gun on their motor boats. Over 600 naval versions of the cannon were built at the British United Shoe Machinery Company in Leicester."

"The gun on display is a Mk II, model BH with a 12 round magazine intended for Hurricane IID tank busting aircraft. It is on display from the RAF Museum, Hendon."