Early warning sound mirrors

[Denge acoustic mirrors]

A forerunner of radar, acoustic mirrors were built on the south and northeast coasts of England between about 1916 and the 1930s. The ‘listening ears’ were intended to provide early warning of incoming enemy aeroplanes and airships about to attack coastal towns. With the development of faster aircraft the sound mirrors became less useful, as an aircraft would be within sight by the time it had been located, and radar finally rendered the mirrors obsolete.

The sound mirrors at Denge in Kent have become quite famous, but it is less well known that a number of other mirrors existed, built to a range of different designs. These webpages bring together photographs of the surviving mirrors, and some details of where they are if you are interested in visiting them.

During World War I sound mirrors were built along the northeast coast, at

Mirrors were also built on the south coast at various times and locations

One mirror was built overseas, at

A different style of aeroplane detection system was tried on Romney Marsh

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Modern mirrors working on similar principles have been built for art, education and entertainment. Some examples are