First World War Early Warning Acoustic Mirror
Case study: Namey Hill, 570m north of Carley Hill Cricket Ground, Sunderland, Tyne & Wear SR5 1JT (North East)
List entry number: 1020325
Background and history
Aircraft began to be used as offensive weapons in the First World War (WWI, WW1). This new threat of long range, strategic bombing provoked the development of new systems of defence for the UK. One such early warning system utilised acoustic detection. Several experimental sound-detecting acoustic dishes were built at strategic locations around the south and east coasts of England.
The acoustic mirror at Fulwell is a rare surviving example. It is one of only four known survivals in the North East of England. It was built following an airship attack on Sunderland in 1916.
The principle of acoustic detection is relatively straightforward. A receiving dish reflects the sound of distant aircraft engines to a focal point. There it is detected by a human listener located in a trench in front of the dish. Later, microphones were placed on a metal post in front of the dish. The reflected sound was transmitted to the headphones of the operator. Under ideal conditions the sound of approaching aircraft and ships could be received from 20 miles away. This could give the people of Sunderland about 15 minutes warning that an attack was coming.
The mirror is `U'-shaped in plan. The back wall is approximately 4.5m high and has a shallow smooth circular 'bowl' shaped into its centre. The side walls have sloping tops and the whole is of very basic mass concrete construction.
Is it at risk?
No. Having been on the Heritage at Risk Register for six years the acoustic mirror is no longer at risk.
The removal follows an extensive programme of repair, landscaping and the creation of a new interpretation panel. This was completed in May 2015.
What's the current situation?
Now the mirror has been rescued, it's possible to visit it and appreciate its location and function.
The site is managed by Sunderland City Council. It is open to the public at any reasonable time. Access is from the A1018 or from the Fulwell Quarry Nature Reserve.