Photograph of a French aviator downing a German observation balloon near St. Mihiel on September 16, 1918, the last day of the American St. Mihiel Offensive. That same day American airmen Frank Luke and Joe Wehner downed three balloons in the sector.

French aviator downing a german observer near St Mihiel on the 16th day of september 1918

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Observation balloon, such as the German sausage, were tethered gas bags with a dangling gondola in which observers could overlook the battlefield. Because their intelligence value was great and they were highly vulnerable, observation balloons were an important target, heavily defended by anti-aircraft guns and patrolling aircraft.

The Belgian Willy Coppens and the American Frank Luke were "balloon busters," and achieved many of their victories destroying observation balloons.

Observation Balloon is a balloon.