The best fighter plane constructed in France, which was used by the French Air Force during World War II, was the low-wing monoplane Dewoitine D.520 whose series was completed by 1939. In 1936, it was further developed from its predecessor the D 500 by a team due to an announcement from the French designer Emile Dewoitine. At this time, Dewoitine was wrapped up with his company in the governmental SNCA du Midi (Societé Nationale de Constructions Aéronautiques du Midi).
The first of the three prototypes took off on October 1938 with an opened cockpit, powered by a liquid-cooled Hispano-Suiza 12Y-21 engine with 890 PS. It did not leave a good overall impression since it overheated and never attained the goal of reaching a speed of 520 km/h.
The Dewoitine D.520 had only one substantial disadvantage: when the Germans began their offensive in May 1940, of the 2,320 aircrafts which were ordered (2,200 by the French Air Force, 130 by the Marines) only 36 were delivered; too few to be able to defy the Germans. The French industry completed a total of 437 aircrafts until the armistice on June 25, 1940, of which 351 made it to the front line of battle. The air squadrons of D.520 were able to shoot down 147 German aircrafts while incurring only 85 casualties of their own. The highly maneuverable and versatile fighter airplanes arrived on the scene too late to precipitate a decisive turning point in the war in favor of the French.
The D.520 was originally conceived of as a cantilever low-wing airplane. The wing assembly was a pronounced V-formation and the nose of the aircraft was configured around the engine. The Hispano-Suiza 12Y 45 engine with Szydlowski-loader powered the aircraft. The first aircraft of the series production took off on November 2, 1939. It was powered by a 830 PS-strong Hispano-Suiza 12Y-31 engine, had a curved front window and was armed with two 7.5-mm-MG's which were situated under the wings. The fuselage was approximately 50 cm long after the prototypes and engine cover were altered. Furthermore, there were two additional tanks on the wings and a safety device behind the pilot's seat.
The machines of the second series were powered by stronger 910 PS-Hispano-Suiza 12Y-45 engines and had an electric propeller with three blades. The armament consisted of a 20-mm-cannon, which shot through the propeller hub and four 7.5-mm-MG's in the wings. The curved front window of the first series was replaced by an optical surface that did not distorted images.
After the armistice with France in June 1940, the German authorities allowed the further production of the D.520. The Vichy-Armed Forces utilized the D.520 as a standard fighter in North Africa and Syria. When the Vichy Zone was occupied in November 1942, the Germans requisitioned 411 aircrafts of this model and used them mostly as fighter training aircrafts in the German Luftwaffe. Other aircrafts were distributed to the Bulgarian, Italian and Romanian allies and came to the front lines of battle.
By the end of 1944, the many remaining D.520 aircrafts were demanded back by the Liberated French Armed Forces. These aircrafts were then used again against the withdrawn German units in southern France. A few of the D.520 DC modeled aircrafts (DC for "Double Control") were transformed into two-seater training aircrafts after end of the war and served in small numbers until the beginning of the 1950s. The last D.520 was flown in September 1953.
Variations of the D.520 were the D.521, which was powered by a Rolls-Royce Merlin III in-line engine with 1,044 PS (768 kW), however, never made it into the series and whose Merlin-engine was traded for a Hispano-Suiza 12Z with 1,200 PS (883 kW) and was then renamed D.524. This project was also not pursued.
There were a total of 905 copies of the series model D.520 constructed with extended fuselage, armoring and stronger wing armament; 437 of which were constructed before the armistice of June 25, 1940 and 468 constructed afterwards. Counting both variations and the three prototypes, the entire production is estimated to be 910 copies.
A D.520 is on display at the Musée de l'Air in Le Bourget in Paris.
The D.520 was Emile Dewoitine's last project in France. Afterwards he went to Argentina where he worked as an aircraft designer.