Early warning sound mirrors

SOUND MIRROR

Acoustic Detection Post, Acoustic Mirror, Acoustic Wall, Listening Post, Sound Dish.

An early warning structure built during and after WWI along the south and east coasts of England. Sound detecting acoustic dishes and walls could detect the sound of approaching enemy aircraft at a distance of 8 to 15 miles.

Royal Commission on the Historical Monuments of England

For ease of management, updates and oddments of further information now live on my blog.

A forerunner of Radar, acoustic mirrors were built on the south and northeast coasts of England between about 1916 and the 1930s. The 'listening ears' were intended to provide early warning of incoming enemy aeroplanes and airships about to attack coastal towns. With the development of faster aircraft the sound mirrors became less useful, as an aircraft would be within sight by the time it had been located, and radar finally rendered the mirrors obsolete.

Though the sound mirrors at Denge are fairly famous, it is less well known that a number of other mirrors existed, built to a range of different designs. In these pages I have collected some photographs of the surviving mirrors, and some details of where they are if you are interested in visiting them.

Northern mirrors

Information about the northern (and Selsey) mirrors is sketchy to non-existent. Even the suggested dates for their construction is guesswork. Do you know anything about them? Have you seen something published in a book, newspaper or magazine, did a relative tell you a story about them, have you found details in an archive, do you know of any other mirror locations? Why were the locations selected, and when were the mirrors built?

If you can offer even a scrap of information, please drop me an email - any information at all would be useful!

Mirrors were built in the north east, at

Boulby, North Yorkshire
Hartlepool(?) (demolished)
Kilnsea, East Yorkshire
Redcar
Sunderland

on the south coast at

Abbot's Cliff, east of Folkestone, Kent
Denge, Dungeness, Kent
Hythe, Kent
East of Dover, Kent
Selsey, West Sussex
Warden Point, Isle of Sheppey, Kent.
Plus a modern mirror by the Royal Military Canal in Kent.

A different style of aeroplane detection system was tried on Romney Marsh

Snave, horizontal disc

At least one mirror was built overseas, at

Maghtab, Malta.

Other sites?

Tom Barrett e-mails to say that at Felixstowe there was a wall type mirror similar to the one at Denge, on a piece of land adjoining the remains of an old fort and martello tower at Felixstowe on the bank of the river Orwell about 1.5 miles upstream from Landgaurd fort. This was a great area for us schoolboys and we were very intrigued when the construction began around 1934. I suspect that it had a very short life as I seem to remember that it had been removed at the time WW2. The area is now completly covered by the Felixstowe container port.

If you can provide any more details about sound mirrors please get in touch with me. I would be particularly interested in any photographs which I could add to this website, especially of the mirrors I haven't yet got pictures of.

Updates

For ease of management, updates and oddments of further information now live on my blog.

Links

[Front cover of the book Echoes from the Sky]

The book Echoes from the Sky by Richard N Scarth (published by Hythe Civic Society) gives a detailed history of the sound mirrors and associated research projects, and is essential reading if you are interested in the story behind the mirrors. Unfortunately it is now out of print, and the Civic Society don't have any more copies for sale.

Pages about acoustic mirrors

There is a history of the south coast sound mirrors by Phil Hide at the Cantiaci Time Team Forum Friends website.
The White Cliffs Underground site has photographs of the ruined mirror at Warden Point on the Isle of Sheppey, the mirror east of Folkestone at Abbot's Cliff, and at Langdon Bay east of Dover, as well as the Lade (Dungeness) mirrors and wall.
A description of how the sound mirrors worked.
More photos of Abbots's Cliff, Hythe and Denge on the Coast Drive website.
Before radar - acoustic detection of aircraft.
Simon Wood's photographs of sound mirrors.
Sound Mirrors and Acoustic Location. Weird and wonderful portable and static ones from around the world at the Museum of RetroTech.
Clive Kidd adds: Sound mirrors get several mentions in The Baby Killers - German Air Raids on Britain in the First World War by Thomas Fegan, (Leo Cooper, 2003 ISBN 0-85052-893-3). Pp153-4 Boulby and Redcar, pp176-7 Sunderland and p116 Kilnsea, briefly outlining a system of quadrants for plotting.

EW Sockett in Tyne Tees Defended:1 in World War 1 1914-18 RNAS RFC RAAF (ISBN 0952 8217 02) gives maps and further details of three north-east coast mirrors and WW1 observer lines. Also gets a write up in in T/T Defended II 1914-1941 ISBN 0-952-8217-1-0. He also gives lots of references to other articles (mainly in the Yorkshire Antiquites Journal) he has written on Tyne Tees Defences.

Prof R W F Burns gives them a small bit in his IEE Hist of Tech paper on the detection and loction of aircraft and refers to a paper in Kew PRO "report 87 Preliminary report on Joss Gap Station of the acoustical section SEE W S Tucker 22 Sep 1920 AVIA 23/84 PRO Kew. Also has a ref to "Locationof a/c by sound Journal of the American physical Society Vol XiV N02 1919 PP166-7.

Sound mirror art

"An ambitious project to create a unique cross-Channel communications link via sound mirrors" at Folkestone and Sangate is mentioned in a Shepway District Council press release of 2003-07-22: Sound Mirror Site Visit Reflects Entente Cordiale.
Return of sound mirrors that trapped Zeppelins, a report on the art project from the 2001-01-29 Daily Telegraph.
More from the Arts Council
Turin Brakes and Blank & Jones have used pictures of the Denge mirrors on some CD covers.
Sound Mirrors by Tacita Dean. 1999, 16mm black and white, optical sound, 7 mins. The soundtrack to this film is entirely recorded within the 200 ft mirror at Denge.

Pages about related topics

Some photos I took of a World War II bombing decoy near Kingston upon Hull.
The Defence of Britain database has records of the 20th century militarised landscape of the United Kingdom.
The Pillbox Study Group website.
World War II pillboxes and anti-invasion defences.
There are some modern sound mirrors used to explain reflection and diffraction of sound at Jodrell Bank Visitor Centre.

A gratuitous picture of some North Sea waves breaking on the sand at Spurn Head on a windy December afternoon.