The Dewoitine D.520 was perhaps the best fighter available to the Armee de l'Air during the German invasion of France in May of 1940 and was an example of a combat aircraft which flew on both sides during World War II. It was a single-seat, low-winged fighter powered by a 900 hp liquid-cooled Hispano-Suiza 12Y Vee-type engine and was designed in November 1936 by a team led by Emile Dewoitine. It was to have a maximum speed of 323 mph (520 km/hr) and given the designation D.520 with the 520 standing for the maximum speed in kilometers per hour.