Editing Dewoitine D.520 (section)

===Background===
On 13 July 1934, the French Air Force launched a new technical programme, under which the development of improved fighter aircraft to improve upon the [[Dewoitine D.500|Dewoitine D.510]], which was yet to enter service at that point but was already considered to be obsolete in the face of rapid advances being made in several European nations.<ref name="Danel 3">Danel 1971, p. 3.</ref> While French aircraft company [[Dewoitine]] initially responded with an improved design based on the D.510, designated as the [[Dewoitine D.500|D.513]], this quickly proved to be inferior to the in-development [[Morane-Saulnier M.S.406|Morane-Saulnier M.S.405]], a domestic competitor.<ref name="Danel 3"/>

In response to a specification for a new fighter promulgated by the French Air Ministry on 15 June 1936, [[Émile Dewoitine]], owner and founder of Dewoitine, formed a new private design office and ordered the firm's chief engineer, Robert Castello, to immediately study the development of a new fighter.<ref name="Danel 3"/> The envisioned aircraft would be as affordable as possible, be powered by the new {{cvt|900|hp|order=flip}} [[Hispano-Suiza 12Y]]21 liquid-cooled engine, and be capable of attaining {{cvt|500|km/h}}. However, the corresponding design was promptly rejected by the Air Ministry.<ref name="Danel 3"/> The design had been rejected by the French Air Ministry, which, after being impressed by the British [[Hawker Hurricane]] and [[Supermarine Spitfire]], had decided to respond by uprating the specifications to include a maximum speed requirement of {{cvt|500|km/h}}.<ref name="Dan30"/>

Accordingly, work on what would become the D.520 commenced in September 1936; according to aviation author Raymond Danel, the D.520 designation was a deliberate reference to the required speed of the aircraft.<ref name="Dan30"/> During January 1937, this revised design proposal was submitted to the Service Technique Aeronautique (STA); while the STAe found the design to be likely to conform with the specified requirements, no order for prototypes to be built was immediately forthcoming.<ref name="Danel 3 4">Danel 1971, pp. 3–4.</ref> By this point, official attention was oriented towards the MS.405, which had already been selected for the re-equipment effort.<ref name="Danel 4">Danel 1971, p. 4.</ref>