The National Heritage List for England identifies the buildings, sites and landscapes which receive special protection.
— Historic England (@HistoricEngland) December 19, 2017
Accoustic Mirrors, Fan Bay, St Margaret’s at Cliffe, Kent
The threat of aerial warfare in the 20th century provoked new systems of strategic air defence. Acoustic mirrors reflected the sound of distant aircraft onto a focal point where it was detected. The examples at Fan Bay are unusual as they are carved from the cliff face. The eastern mirror is one of the earliest, dating from about 1916. A second mirror dates from the early 1920s. The development of radar in the 1930s rendered sound mirrors obsolete. (Scheduled Monument. List Entry Number: 1442235)