As early as 1915, Hugo Junkers was working on an all-metal low-wing aircraft. This innovative concept was rejected by the Luftstreitkräfte despite the duralumin structure that offered pilots relatively greater safety. Finally, the J.9 design was approved, designated D-I but only arrived to front line pilots in the last months of the war. Despite the qualities of speed and maneuverability, only 41 copies were built, in particular due to a difficult construction. This plane is the only extant example that survives today.

All-metal, except the propeller! Fighter pilots did not like it, but the D.I was the harbinger of a lineage of Junkers airliners.

1918 fighter employing the Junkers corrugated metal construction.