Revolutionary with its corrugated aluminium hull (Duralumin) and low wing, the fast and manoeuvrable prototype of the Junkers J-9 single-seat fighter developed by Hugo Junkers in 1915 was initially rejected by the German army. Eventually approved by the military, twelve Junkers J-9s were built from April 1918 onwards. The aircraft preserved in the Musée de l’Air et de l’Espace (Air and Space Museum) was found in a country airfield, left behind when the Germans withdrew following the armistice of 11 November 1918. It is the only one in existence in the world.