03/31/2012. Transferred by the Société Aéronautique Française-Avions Dewoitine to the Lioré et Olivier (LeO) concern owing to the workload imposed on the parent company by the D.50bis (future D.500), the D.37 (later D.370) was a private venture contender in the 1930 C1 program. The prototype, flown on October 1, 1931, was powered by a 700 hp Gnome & Rhône 14Kbrs Mistral Major fourteen-cylinder two-row radial. It was subsequently subjected to an extensive series of modifications: the 14Kbrs engine gave place to a 800 hp 14Kds; the engine cowling was changed; the undercarriage was redesigned, and the wing introduced dihedral and reduced chord.
Yet more redesign was embodied by a second prototype, the D.371, which appeared late February 1934. For the Armee de l'Air 28 D.371s were ordered with the 930 hp 14Kfs engine, and an armament of four underwing 0.295 in (7.5 mm) MAC 34 machineguns. Fourteen were ordered by Lithuania, and these, having two synchronized 0.303 in (7.7 mm) Browning guns in the fuselage and two Darne guns of similar caliber in the wings, were designated D.372s. Twenty were ordered for the Aeronautique Navale as D.373s, these having flotation gear, an 11.81 in (30 cm) reduction in wing span and an armament of four Darne guns within the wing. A further 25 ordered for this service with aft-folding wings were designated as D.376s.
The last D.371 left the factory at the end of December 1935, the Armee de l'Air fighters following the Navy's D.373s. The Lithuanian government meanwhile relinquished its D.372s in favor of D.501s, the former being sold to the Spanish Republican government and ferried to Spain during August 1936, where they were later joined by ten of the 28 Armee de l'Air D.371s. The remaining D.371s equipped an escadrille at Bizerte, Tunis, until 1939, but were little flown owing to constant problems with their engines. The D.373s and D.376s of the Aeronautique Navale suffered similarly, and by September 1939, only thirteen D.373s and nine D.376s were on strength, all being withdrawn before the year's end.