On the 1st April 1916 a German Zeppelin raided the Wear and it's industries. The Eastern and Southern Coast was the original target, but winds blew the airship to the North-east. Following a raid on Tyneside on 16th June 1915 the defences had been strengthened there so the captain headed for the River Wear. The South bank of the river received the deadly payload of high explosives and incendiary bombs at Millfield and Deptford. The Zeppelin then crossed the river and turned its focus on Monkwearmouth. In all 22 people were killed, 25 seriously injured and over 100 had less serious injuries as Monkwearmouth Station, Thomas Street School, Victor Street and Whitburn Street took hits. In reporting the raid the local paper, the Sunderland Echo, downplayed it to three small fires easily dealt with and that people kept calm. This was to prevent widespread panic. Under fire from a gun in Fulwell the Airship turned South again dropping more ordinance on the docks before flying to Middlesbrough to wreak further destruction.
An acoustic mirror was built here to give 15 minutes warning of an impending attack by Zeppelin. It worked by reflecting and focusing the sound of the engine on to a microphone placed in front of the concave mirror. Other Acoustic mirrors had a static microphone (a trumpet shaped sound collector) on a pole, although it is thought the microphone here was suspended between the side walls to enable it to be moved. Elsewhere an operator listed to the output in a trench to the front yet there is no evidence of a trench here leading to a suggestion a hut housed the operator.
It is not known exactly when this acoustic mirror was built, but even if thrown up quickly following the raid in 1916, technological advances lead to Zeppelin's quickly being moved to just observational status.
Until very recently the monument was on the English Heritage At Risk Register. It has now had restoration work done to it which includes gravel access and an interpretation board. When I first viewed it there was a significant coverage of undergrowth, much of which has been cleared.
Although the track from Newcastle Road is tarmacadammed, there is a warning prohibiting unauthorised vehicular access.
The cache is a 35mm film canister.