A British Airco D.H. 2 destroys a German observation balloon but has paid for it. The aircraft has also been destroyed by a German anti-aircraft gun called a "flaming onion" which 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 term could also be applied to any sort of anti-aircraft fire that used a visible tracer.
The actual weapon was a Gatling type, smooth bore, short barreled automatic revolver called a 'lichtspucker' (light spitter) that was designed to fire flares at low velocity in rapid sequence across a battle area. This gun had five barrels and could launch a 37 mm artillery shell about five thousand feet (1500 m). To maximize the chance of a strike, all five rounds were discharged as rapidly as possible, giving the 'string of flaming onions' effect. Because most other rounds were fired slowly due to the nature of anti-aircraft artillery at the time, this gun's rapid rate of fire left many fliers thinking that the rounds were attached to a string and they feared being shredded by it.
Credits: The aircraft, balloon and groundwork is based on a flight from Rise of Flight, the sky is from my collections of mayyang.com skies. All editing done with GIMP.
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