The Browning .303 Mark II was the standard gun used on British aircraft during the 1930s and Second World War. It was adopted by the Royal Air Force (RAF) and manufactured under license by Vickers Armstrong and BSA. The design was based on the 1930 Pattern belt-fed Colt-Browning machine gun with a few minor modifications. The muzzle extension was prone to fouling from the cordite-based ammunition and the RAF redesigned the muzzle extension with chrome plating it to make the surface smoother and cooling fins were also added.

    The gun was designed to fire hydraulically as a wing-mounted machine gun on the Supermarine Spitfire and Hawker Hurricane and as hand-fired mount for use in Avro Lancaster bombers and reconnaissance aircraft. It had a rate of fire of 1,150 rounds per minute a muzzle velocity of 2,660 ft/sec. The major advantages were that it was lighter, accurate, and available in large numbers. Near the end of the war, the RAF began adopting .50 caliber machine guns in their bombers.