Newcastle Road, Acoustic mirror

The Fulwell mirror has been revealed recently in modern reclamation work, and was designed to keep at bay German zeppelins. Examples of acoustic mirrors have long been known at RAF Biggin Hill and on the Kentish Coast, as well as in Malta. The mirrors are of three types. The Fulwell dish mirror was one of the Coastal Watcher type or Track Plotting Mirrors. It would have supplemented information derived from other sources such as the Radio Direction finding Stations, for example the Stockton on Tees Y station. This had a limited range of some 15 to 20 miles and was capable of giving a 4 minute Early Warning Alarm via London or the Senior Naval officers at Newcastle or Hull. The technology of these mirrors was remarkably modern. A signal was reflected by the dish to a collector head and thence to a receiver. The modus operandi was for the Duty Observer or 'Listener' to take up position in a bunker, usually in front of the 15ft mirror with the stethoscope head-set connecting him to the collector head, usually an amplified microphone, above his own head. The optimum sound effect received, coupled with the Doppler effect, nicely illustrated the track of the intruder. By evolving an excellent reporting system, its course could be tracked and plotted sufficiently accurately to allow the anti-aircraft defences to take defensive action. The Fulwell mirror was of a similar type to the two Yorkshire examples at Redcar and Boulby. The Fulwell example consisted of an 11ft high rear wall, some 18ft across, containing a 15ft mirror. This was made possible because the mirror was tilted backwards so that its axis was above the horizontal. This provides some evidence that its original purpose was to detect aircraft and not ships. It had two short walls for stability and to exclude ground noises. The noise of an approaching zeppelin's engine could be picked up some 15 minutes away. The Fulwell example has its own interest in that not only does the whole mirror seem somewhat smaller than the Redcar example, but the collector head may have been secured in front of the mirror by wires across the arms, so allowing the head to be variably positioned, unlike the fixed stand-pipe still surviving at Kilnsea. The Fulwell Mirror probably dates to the 1917-1918 period. A watching brief revealed projecting concrete foundations within the immediate curtilage of the mirror which may have been a raft or plinth and a concrete plinth of a pyramidal shape surrounding a hollow metal column or pipe. A similar construction to this has been noted at Kilnsea and interpreted as a listening post. The Kilnsea example was previously thought to be the only surviving example. There is no evidence of a listening trench in front of the mirror. SCHEDULED MONUMENT AND LISTED GRADE 2