Early Warning Systems (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 aircraft.

(taken from: http://www.andrewgrantham.co.uk/soundmirrors/locations/hythe/)

See also: http://www.andrewgrantham.co.uk/soundmirrors/

[Hythe sound mirror, May 2003]30 ft sound mirror, Hythe