The small, hub-firing Morane-Saulnier MS.406 was the most numerous French fighter at the time of the German invasion in May 1940. Unfortunately for the French, it was also the poorest of the three front-line designs available at the time (the others being the MB.152 and D.520) with performance figures markedly inferior to both British and German designs of the period. It was also hampered by complexity of design which made it difficult to mass produce, a problem exacerbated by France's pre-war industrial negligence. Service difficulties actually reduced the number available but still, 19 out of 26 French fighter groups were equipped with the MS.406 which scored a total of 175 kills with losses amounting to about 150 in combat with another 100 lost on the ground. The MS.406 was exported to Finland, Turkey and Switzerland (where it was also built locally) before the surrender while surviving units were sent to Croatia and Italy.

The prototype MS.405 first flew on 20 May 1938 and was followed by the MS.406 main production variant which was the backbone of the French fighter force in World War II. Further development led to the MS.410 with increased wing armament although these were all conversions of MS.406 aircraft. Swiss versions were designated D-3800 and differed by the inclusion of the MS.405 wing design while later, the MS.412/D-3801 featured a more powerful engine and were built domestically well up to the late 1940s.