Of all the fascinating sights and histories of Romney Marsh one of the most unusual are the Sound Mirrors or listening ears found near Dungness. A precursor to radar, these huge concrete constructions were designed to provide an early warning of enemy air-forces from 1st World War onwards.

Remarkably, the sound mirrors were proven to work and picked up the noise from air craft engines across the channel well before they were visible to the eye. Like satellite dishes, the sound mirrors reflected sound waves to a microphone at the foci - central point - amplifying the sound and enabling sounds from engines many miles away to be heard. In one experiment, the noise from a Zepline airship was reported to have been heard upto 20 miles away while another detected incoming planes at upto 30 miles away.

Sound mirrors were constructed at Dover, the Thames Estuary, near Sittingborne, at Dungeness and North East Coast. The three at Dungeness were 20feet, 30feet and 200 feet in diameter. The largest used for general detection while the smaller models - equipped with microphones - were to narrow down location and direction.

Sound mirrors at saw action in 1917 and 1918 with the Dover units detecting an enemy raid when it was still 15 miles from the coast¹. Three sound mirrors at Dungeness survive and these in conjunction with mirrors elsewhere across the South East played an active part in Englands air defenses until the 2nd World War.

The listening ears not only provided direct early warning of incoming air attack but also played a key role in establishing the processes and infrastructure that would later be used for radar. To process the information from the sound mirrors across the South East a command and central control station was set-up in London - this providing the basis for radar defense command control in the 2nd World War.

Sound mirrors were abandoned in the late 1930's as a defense measure following the introduction of faster plans. By the time invading planes had been heard and located3, they had already travelled to within viewing distance² invalidating the need for the mirrors. 

The mirrors are now on an island, surrounded by a lake caused by gravel extraction, and under the protection and preservation of English Heritage with local authorities providing visitor information³.

References:

1: http://www.doramusic.com/soundmirrors.htm 

2: Wikipedia page on sound mirrors 

3: http://www.ajg41.clara.co.uk/mirrors/dungeness.html

http://www.ajg41.clara.co.uk/mirrors/index.html - Andrew Grantham's page on sound mirrors.

Last update: 30-07-2008 12:39