The French designed Morane-Saulnier M.S.406 fighter saw combat in the Battle of France in 1940. The French were working on an improved version known as the M.S.412 but due to the fall of France in 1940 it was not continued until the Swiss took up the design and developed the D-3801 fighter from it (the Swiss had previously licence-built 84 of the M.S.406 fighter between 1939 and 1940. It was known as the D-3800). The development work was primarily completed by EKW (Eidgenoessisches Konstruktionswerkstaetten or “Federal Constructions Works”).
The Morane-Saulnier D-3801 was powered by a licence-built version of the same Hispano-Suiza 12Y engine as the M.S.406 and armed with a 20mm cannon and 2 x 7.5mm machine guns. 207 D-3801 aircraft were manufactured in Switzerland for delivery to the Swiss Air Force between 1941 to 1945.
A beautifully restored Morane-Saulnier D-3801 (J-276) can be seen today at the Swiss Air Force Centre in Dübendorf (Flieger Flab Museum). Red and white neutrality stripes were applied for easy recognition by both Allied and German pilots.
The D-3801 fighters were retired from front-line Swiss service when North American P-51D Mustang fighters came into service in 1948 but the last D-3801 was not retired from a training and target-tug role until 1959. Although a small number of interned USAAF P-51 variants were used by the Swiss during World War Two, 130 P-51D’s were officially purchased from US surplus stock and were operated until 1958.