photo credit: csstudios

from 1915 onwards these huge eerie concrete structures started popping up along the uk coast, all built with one purpose: to provide the military with an early warning system in relation to incoming aircraft. their construction was pretty much limited to the uk and arrived just before radar technology as we know it became widespread.



photo credit: get down

the majority of sound mirrors actually built were large concrete parabolic or hemispherical dishes tilted at a slight angle towards the sky, manned by an operator either behind or underneath the dish in a special chamber. the dish would reflect the incoming engine sounds onto a large movable microphone placed at the focus of the mirror and enable the operator to judge the distance and direction of the approaching aircraft.



photo credit: feersumendjinn

in 1930 the military also decided to build a massive 200ft long sound mirror wall at denge, a then raf base in kent. obviously its size resulted in greater accuracy and range with an unaided ear able to detect aircraft from 6.5 miles on a clear day. that coupled with the use of the microphones gave the operator a range of over 20 miles.



here’s the direct google maps link to the old air base where you can still see the mirror wall and 2 other more common sound mirror dishes. the original plan was to place the mirror walls along the entire coast, every 25 miles or so, with a couple of smaller dishes in between each one. in the 1930s radar reared its head and aircraft became too fast to make this method of detection advantageous so the military dropped the idea and left the mirrors intact. many of them remain to this day, scattered along the south east coast.
for more info about sound mirrors…

1, 2, 3, 4