Another 17 were built from spares between 1947 and 1948. Reliability of the new engine was at first extremely poor, with problems with crankshaft bearings causing several accidents. The engine problems slowed deliveries, with only 16 aircraft produced in 1942 and a single aircraft delivered in 1943. The engine problems were eventually resolved in 1944. With from the Hispano-Suiza 12Y-51, the speed was boosted to , roughly equivalent to the D.520 or the Hurricane. Weights were between . After being retired from operational use as a fighter when the North American P-51 Mustang was acquired in 1948, the type remained in service as a trainer and target tug until 1959. The D.3802 was based on the MS.450, emerging as the MS.540, with a Saurer YS-2 engine. The prototype flew in the autumn of 1944, revealing several shortcomings, but it was capable of . 12 were produced seeing limited use with Fliegerstaffel 17 and some other units. The last development of this aircraft was the D.3803, with Saurer YS-3 engine, and modified dorsal fuselage (with an all-round visibility canopy). The D.3803 was armed with three HS-404 cannon (one in the nose, two in the wings), plus up to bombs and rockets. Despite not having a powerful engine, the type reached at . The performance was impressive, but the last development of this 1935 fighter design had several shortcomings and was not entirely successful. Its development was halted as P-51D Mustangs became available. France sent 30 Morane-Saulnier to Finland, between 4 and 29 February 1940. By 1943 the Finns had received an additional 46 M.S.406s and 11 M.S.410s purchased from the Germans. By this point, the fighters were hopelessly outdated, but the Finns were so desperate for serviceable aircraft that they decided to start a modification program to bring all of their examples to a new standard. The aircraft designer Aarne Lakomaa turned the obsolete "M-S" into a first rate fighter, the "Mörkö-Morane" ("Mörkö" is the Finnish for "Bogeyman" or "Bugbear"). It is sometimes referred to as the "LaGG-Morane". Powered by captured Klimov M-105P engines (a licensed version of the HS 12Y) of with a fully adjustable propeller, the airframe required some local strengthening and also gained a new and more aerodynamic engine cowling.