Obscura Day 2017! Join our global celebration of exploration and discovery.
May 6

Greatstone, England

Greatstone Sound Mirrors

Huge concrete structures designed as an early warning system for Britain to detect enemy aircraft 

The massive concrete acoustic mirrors, or “listening ears,” lining the southeast coast of England were built between the world wars to monitor the skies for the telltale sounds of airborne invasion.

Built between 1927-30, the sound mirrors were part of Britain’s national defense strategy. Their parabolic shape collected and magnified sound waves in the air over the English Channel and directed them at a microphone positioned just in front of the parabola. Anti-aircraft defenses were then deployed. The mirrors effectively gave Britain a fifteen-minute advance warning of an impending attack.

The site features three different reflectors, including a 200-foot-long curved wall, a 30-foot-tall parabolic dish, and a smaller 20-foot-tall shallow dish. All three can be seen in Greatstone, located in the north east side of the Dungeness Nature Reserve.

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