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The Swiss Air Force was one of the interested parties of the pre-World War 2 French Morane-Saulnier MS.406 fighter design. The line began with the MS.405 and graduated to become the production-quality MS.406 and, to this, the family evolved to include several one-off forms and other production standards – including the MS.406H serving the Swiss Air Force during the war as the “D-3800” (detailed elsewhere on this site).

Another entry into the Swiss MS.406 story became the “MS.412” – known locally as the “D-3801”. This was a further modification of the MS.406 line that switched to the Hispano-Suiza 12Y-51 inline engine of 1,050 horsepower (take-off). Armament followed the standard set by the D-3800: 4 x 7.5mm machine guns (belt-fed) and a hub-mounted 20mm Hispano-Suiza HS.404 autocannon. Additionally, a simpler, fixed radiator unit was used instead of the original retractable type. However, the German advance on France during May-June 1940 meant that the project was to be completed in Switzerland – who also remained under the very real threat of invasion.

As in the D-3800, production was handled locally (under license) by Eidgenpssisches Flugzeugwerke (EFK) but this time aided by the likes of Doflug (Dornier-Werke AG) and SWS.

A prototype D-3801 was flown for the first-time in October of 1940 and first-deliveries of production-quality, combat-capable forms followed in 1941 with the last unit delivered in 1945. In all, production ceased after 207 fighters were built for the Swiss Air Force, making the D-3801 a vital contributor to the defense of Switzerland from an invasion that was never to materialized from Germany. As in the D-3800, which saw two examples built up from existing spare parts, a further seventeen D-3801 were only later added to the existing stock – again built from available spares. These arrived in 1947-1948 at which point the Second World War (1939-1945) was all but over.

The D-3801, like the D-3800 before it, served out its days as advanced trainers for the Swiss Air Force and some of the lot were expended as target tugs as late as 1959 (the related D-3800 was given up for good back in 1954).

As finalized, the D-3801 fighters had a maximum speed of 332 miles-per-hour, a climb rate (initial) of 3,290 feet-per-minute, and ranged out to 745 miles. Empty weight was 4,700lb against an MTOW of 6,000lb.