The Doflug D-3802/ Morane-Saulnier M.S.540 was developed in Switzerland from the M.S.450 and was basically an improved version of the M.S.406.
The M.S.450 was developed in France in response to a 1937 call for a new single seat fighter. It used more modern construction methods than the M.S.406, and had a more powerful engine, but was otherwise similar to the earlier fighter. It wasn't accepted for production by the Armée de l'Air, but some development work continued and at some point the modified designs gained the designation M.S.540.
Development of the M.S.450 family ended in France after the armistice of June 1940. Two years later the Dornier-Werke AG (Doflug), a Swiss subsidiary of the German company, was asked to develop a single seat fighter to replace the D-3801 (itself a licence built version of the M.S.412, which was a M.S.406 with a more powerful engine). Their response was the D-3802, which took many of the features developed for the M.S.450 and improved on them.
The D-3802 had a similar outline to the M.S.450. The wings were very similar, with a straight tapering trailing edge and a leading edge that tapered sharply close to the fuselage then straightened out but continued to taper on the outer section. The fuselage was an all-metal stressed-skin monocoque, and was visually rather more refined than that of the M.S.450 or the earlier M.S.406, both of which had looked rather bulky. The D-3802's more powerful engine made it the first member of the M.S.406 family to exceed 400mph.
The prototype, which made its maiden flight on 29 September 1944, was armed with one engine mounted 20mm cannon and four wing mounted machine guns. The Swiss then ordered a pre-production series of eleven aircraft, in which the wing mounted machine guns were replaced with two 20mm cannon, giving it a total of three. While these aircraft were being produced development work moved onto the improved D-3803, but eventually neither type was ordered into full production and instead the Swiss decided to purchase war surplus P-51D Mustangs. The twelve D-3802s saw service with Fliegerstaffel 17, remaining in use until 1956.
Engine: Saurer (Hispano-Suiza) YS-2 12-cylinder liquid cooled engine
Span: 32ft 10 1/2in
Height: 10ft 11 ½ in
Empty weight: 5,500lb
Maximum take-off weight: 8,607lb
Max speed: 381mph at 21,325ft
Climb Rate: 2,795ft/ minute
Range: 404 miles
Armament: One engine mounted 20mm cannon and either four wing mounted machine guns or two wing mounted 20mm cannon