[1] The M.19 featured the Oberursel U.III 14-cylinder, two-row rotary engine, combined with the two-bay wing cellule of the Fokker D.I.

[7] Low compression resulted in poor performance at altitude[8] and cooling of the rear row of cylinders proved problematic.

[5] In early October 1916, evaluation of Fokker's M.21 prototype at Adlershof revealed poor construction and workmanship.

[10] While the wings proved acceptable, the fuselage and tail surfaces failed to meet specifications.

[2][10] Idflieg reprimanded Fokker for his firm's substandard construction practices, but permitted D.III production to continue.

Late production aircraft replaced the wing-warping system with horn-balanced ailerons on the upper wing.