Building record TR 07 SW 22 - Early warning: accoustic mirror

A damaged World War II sound mirror on the beach at Walden Point. This example probably dates to between 1917 and 1923. It is the same typology as those installed on the north east coast at Kilnsea, Boulby, Redcar and Fulwell. Generally, sound mirrors were erected on the south and north east coast of England between 1916 and the 1930s as a means of detecting enemy aircraft. They became obsolete with the invention of radar.

The site of a sound mirror located at Warden Point (TR 022 723) built between 1917 and 1923. Sound mirrors were designed to provide early warning of approaching enemy aircraft by detecting the sound of their engine over long distances. The site comprised vertically-mounted concrete slabs with a central shallow dish 15ft (4.6m) in diameter and frontal plinth mountings for microphones. The site could have been in use up until the 1930s when the technology was replaced by radar. (1)

The mirror is in very poor condition having been displaced from its original position by cliff erosion. The mirror is now broken into fragments (at least a half dozen pieces) and appears to have toppled forward from its original location and smashed on landing. The mirror fragments appear to lie mostly below the high water mark and will therefore suffer from further sea damage at high tides. Although the mirror would have been considered of national importance given the rarity of this monument type, its fragmentary nature, present condition and impossibility of retention and positive management in the medium to long term lead to the conclusion that scheduling is not an appropriate course of action in this instance. (2-3)).

<1> Victor Smith and Ron Crowdy, Thames Gateway Assesment: Gazetteer of Defence Sites (Index). SKE6445.

<2> 1946, Photograph (Photograph (Print)). SWX9572.

<3> Dobinson, C, 2000, Twentieth century fortifications in England, volume 7. Acoustics and radar: England's early warning systems 1915-1945 (Bibliographic reference). SWX23709.