The flaming onion was a 37 mm revolving-barrel anti-aircraft gun used by the German army during World War I, the name referring to both the gun, and especially the flares it fired. The American 'balloon-buster' ace, Frank Luke, was a prominent victim of this device, and it was mentioned in Eddie Rickenbacker's book Fighting the Flying Circus and in many "Biggles" stories. The term could also be applied to any sort of anti-aircraft fire that used a visible tracer, appearing in reports of combat from the Battle of Taranto, for instance.