In 1940, Britain was fighting for its life against the Luftwaffe. British aircraft manufacturers couldn't keep up with the huge orders placed by the British Government. So they turned to American manufacturers like Curtiss and North American. Eventually, North American came forward with their own design for a brand new aeroplane. The prototype was brought to the Air Fighting Development Unit (AFDU) at what is now IWM Duxford. It had great potential with a low-drag fuselage and laminar flow wing. But the Allison V12 engine which powered the aircraft struggled above 15,000 ft. So the AFDU decided to try the aircraft with a Rolls Royce Merlin instead. That aircraft became one of the greatest fighters of the Second World War - the P-51 Mustang. The P-51 could fly and fight with British and American bombers all the way to Berlin and back again. Its range was so large that it even began to replace British Spitfires towards the end of the war. On their way back from escort duty Mustangs would also take out targets of opportunity like enemy trucks, barges, and trains. By 1944 the Allies had air superiority over Western Europe, thanks in part to the Mustang. See our Mustangs up close! Visit IWM Duxford: https://www.iwm.org.uk/visits/iwm-duxford Find out how the Second World War was fought from the air: https://www.iwm.org.uk/history/how-the-second-world-war-was-fought-from-the-air See the full list of archive films used in this video, available for licensing and downloading: https://film.iwmcollections.org.uk/c/2571 War in the Air book: https://shop.iwm.org.uk/p/26905/War-In-The-Air---The-Second-World-War-in-Colour