After World War I Hispano-Suiza returned to automobile engine design and, in 1919, introduced the H6, earning them a reputation even greater than that of Rolls-Royce in England. Indeed, Rolls-Royce featured many Hispano-Suiza patented features, under licence. Most notably, Rolls-Royce used for many years the famed Hispano-Suiza power brakes, reputedly the best in the world, which used the torque generated by a drum brake mounted on the transmission shaft to power those on the wheels.
1919 Hispano-Suiza H6 Duvivier Torpedo
1922 Hispano Suiza H6B Brunn Dual Cowl Phaeton
1923 Hispano Suiza H6B Muhlbacher Skiff
1924 Hispano-Suiza H6B Coupe de Ville
1925 Hispano Suiza H6B Convertible Victoria
1927 Hispano Siuza H6C Van Vooren Coupe
1928 Hispano-Suiza H6B Hibbard & Darrin Cabriolet De Ville
1933 Hispano Suiza J12 VanVooren Faux Cabriolet
1934 Hispano Suiza J12 V12 Rotschild Coupe Darrin
1935 Hispano Suiza K6 Brandone Coupe
1937 Hispano Suiza K6 Henri Chapron Coach Mouette
1938 Hispano Suiza - Dubonnet H6
In 1936, with another war clearly looming, Hispano-Suiza was told to stop production of cars and turn solely to aircraft engines once again. At the time they had just introduced a new series of water-cooled V-12 engines and the Hispano-Suiza 12Y was in huge demand for practically every French aircraft. However Hispano was never able to deliver enough of these engines, and many French fighters sat on the ground complete but for the engine.
Another development of the era was a series of 20 mm autocannon, first the Hispano-Suiza HS.9 and then the more famous Hispano-Suiza HS.404. The 404 was licensed for production in Britain and equipped almost all RAF fighter aircraft during the war. Production was also set up in the US, but these versions never matured even though the USAAC and US Navy both wanted to use it in place of their existing .50 weapons.