The commanding officer of the German WWI fighter wing was Manfred von Richthofen, known as ‘The Red Baron’ (German: “der rote Baron”). He was officially credited with 80 air combat victories before he was killed in action. Originally a cavalryman, he transferred to the Air Service in 1915 becoming one of the first members of a fighter squadron.

Richthofen took the flamboyant step of having his Albatross (symbol and insignia) on his fighter plane painted red when he became a squadron commander.

As the ‘Jagdgeschwader 1’ fighter unit expanded and morphed, it became known as “The Flying Circus” or “Richthofen’s Circus” (German: “Der Fliegende Zirkus”). The reasons for the circus name are due to the bright colors of its aircraft (red), and because of the way the unit was transferred from one area of Allied air activity to another- moving like a traveling circus, and frequently setting up tents on improvised airfields.

Members of “The Red Baron’s” fighting unit started painting part of their aircraft red to make their leader less conspicuous, to avoid him being singled out in a fight. In practice, red coloration became a unit identification.

The German high command permitted this practice in spite of the drawbacks regarding Intelligence and used it as propaganda by referring to Richthofen as “Der Rote Kampfflieger” - “the Red Fighter Pilot.”

More Info: en.m.wikipedia.org