The Fokker D.I was a development of the D.II fighter. The D.I was also flown in Austro-Hungarian service as a fighter trainer aircraft under the designation B.III. Confusing the matter further, both the D.II and D.I arrived at the Front in German service at similar times, in July–August 1916. The main designer was Martin Kreutzer.

The Mercedes D.II was a six-cylinder, SOHC valvetrain liquid-cooled inline aircraft engine built by Daimler during the early stages of World War I. Producing about 110 to 120 hp, it was at the low-end of the power range of contemporary engines, and was generally outperformed by rotaries whose power-to-weight ratio tended to be much better. It also had stiff competition from the Ferdinand Porsche-designed 120 hp Austro-Daimler 6. The D.II was produced only briefly as a result, but its design formed the basis for the later Mercedes D.III which saw widespread use throughout the war.