Motorenfabrik Oberursel A.G. was making a variety of types of rotary engine.
The most successful of them was the Oberursel UR II, which was really a copy of the French Le Rhone 9J. The most famous airplane of the Great War, the Fokker Dr.I, had this very engine; and it was with no small thanks to the UR.II that the Dr.I displayed a dogfighting ability to match the airplanes of the enemy.