This World War I coastal watch mirror north of the River Wear at Fulwell in Sunderland is a listening device for detecting approaching Zeppelins – airships developed by the Germans to mount long distance bombing raids on British cities. – and is part of an early warning system designed to protect the Tyne/Wear estuaries.
The technology was the pre-cursor to the radar that was developed shortly before World War II. Although the 15′ concrete dishes were much cruder they were surprisingly effective in their ability to detect aircraft. Details on height and course were calculated by a duty observer who was able to interpret the engine noises picked up in the dish and reflected onto a collector strung in front of the dish. The results were passed to waiting gun batteries giving them a 15 minute warning of the impending raid.
Mirrors of this type – similar to those at Redcar and Boulby – were installed after Sunderland had suffered a devastating raid on 1st April 1916. A zeppelin flying down the river towards the sea dropped its bomb-load north of the Monkwearmouth Bridge where the high explosive and incendiaries caused havoc, killing 22 people and injuring over 100, particularly in the Wheatsheaf area of the city where a tram laden with passengers was hit.
The mirror is a Scheduled Ancient Monument and is Grade II-listed. It is located on Namey Hill, 570 m north of Carley Hill Cricket Ground (Grid reference NZ390597).