Definition
A large, unmanned, tethered balloon flown at altitude as a passive aerial defense, used to deny low-flying enemy aircraft access to a protected area. The balloon and its mooring cables present a physical hazard that forces attacking aircraft to fly higher, where they are more easily engaged by anti-aircraft fire, or to risk striking the cable.
Plain English
A big balloon held in place by a strong cable, flown over an area to keep enemy aircraft from flying low over it. The cable itself is the threat — aircraft that hit it can be damaged or destroyed.
Context Anchor
Seen mainly in military and historical aviation discussions, especially about defending cities, ships, or important facilities from low-flying aircraft.
Derivation
From the French 'barrage,' meaning a barrier or dam. The balloon acts as a barrier in the sky, blocking low-altitude approaches the same way a dam blocks a river.
Why Pilots Care
Tethered balloons and their cables are a real flight hazard wherever they are deployed. Modern tethered aerostats used for surveillance or communications are charted obstacles, and pilots must give them and their mooring cables wide clearance.
Grounding Statement
Picture a protected harbor with large balloons held overhead by cables, forcing attacking aircraft to stay higher or avoid the area.
Intuition Check
Do not think of barrage here as gunfire. Here, barrage means a barrier made by balloons and cables.
Example Sentence 1
During the Battle of Britain, barrage balloons were flown over London to force German bombers to attack from higher altitudes.
Example Sentence 2
Pilots studied barrage balloon placements on maps before planning routes over defended areas.