The Oberursel U.I was a 9-cylinder rotary engine rated at approximately 100 hp. It was a German license-built copy of the French Gnome Lambda and became one of the most widely used powerplants in the early years of the Great War. Thanks to its relatively light weight and reliability (by rotary standards), it powered many of the aircraft that shaped the first air battles of 1915–1916.

Aircraft using the Oberursel U.I:

• Fokker E.I – the very first of the famous "Eindecker" fighters.
• Fokker E.II – improved version with more power and armament.
• Fokker E.III – the best-known and most numerous of the Eindecker series.
• Fokker D.I – early biplane fighter, transitional design after the monoplanes.
• Fokker D.II – another step in Fokker’s biplane development.
• Fokker A.III (M.8) and Fokker M.5 prototypes – unarmed reconnaissance and trainer aircraft, predecessors of the Eindeckers.
• Pfalz E.I, E.II, E.III – license-built Morane-Saulnier monoplanes equipped with the U.I.
• Pfalz A-type parasols – reconnaissance machines derived from Morane designs.
• Roland D.I "Haifisch" – early test versions flew with the U.I before switching to inline Mercedes engines.

Various prototypes and training aircraft where the U.I was installed for testing or limited operational use.

Historical significance

Engines like the Oberursel U.I gave the German Air Service its first real fighter aircraft. In the hands of skilled pilots, the Fokker monoplanes armed with synchronized machine guns brought about the short-lived but notorious "Fokker Scourge" of late 1915 to early 1916.{{freeshipping_code_1}}{{payment}}