Evolved in parallel with the D 9 as a contender in the 1923 C1 programme, in which it was eventually to take third place after the Nieuport-Delage 42 and the Gourdou- Leseurre 32, the D 12 differed essentially in engine type. Possessing a basically similar fuselage to that of the D 1, the D 12 was powered by a 450hp Lorraine- Dietrich 12EW 12-cylinder W-type water-cooled engine. First flown, like the D 9, in June 1924, the D 12 had an armament of two 7.7mm Vickers guns, and, in September, was fitted with a higher compression ratio 12Eb engine and a pair of 7.5mm Darne modele 19 guns on the wing centre section. The paired Lamblin radiators on the undercarriage legs gave place to a frontal radiator and a wing similar to that finally adopted on the D 9 was fitted. On 5 February 1926, the D 12 was written off in an accident at Cazaux. A second prototype had meanwhile entered flight test, having flown at the end of 1925, this having a W-type Hispano-Suiza 12Gb engine, but further development was discontinued.