Fulwell Acoustic Mirror

Fulwell Acoustic Mirror is a 4m high concave concrete dish, constructed on the coast at Fulwell, Sunderland. Completed in 1917, it was designed to act as an acoustic early warning system against air raids, after a bomb dropped by a Zeppelin over the Wheatsheaf area of Sunderland in April 1916 left 22 people dead and more than 100 injured.
The mirror worked by reflecting sound detected by a microphone in front of the dish to an operator with headphones who could alert the authorities of approaching Zeppelins. Using sound detection methods learnt in the trenches it was designed to give a 15 minute warning of approaching enemy airships.