larger machine-guns during WWII. CITiZAN’s northern team recently returned to Bridlington with a group of volunteers to survey the remains of a square pillbox that had been recorded in the 1990s. Although this fortification was designed to forestall a German invasion, it has proved no match for the sea, and now lies shattered on the foreshore. The largest fragment is wedged against a WWII anti-tank block, and only one of the two embrasures noted in the 1990s could be identified with any certainty during CITiZAN’s 2016 survey. Being constantly battered by the waves, even such seemingly sturdy brick and concrete remains are unlikely to survive a century hence.
ABOVE One of the two sound mirrors erected at Fan Bay, Dover. These devices were designed to detect the sound of approaching aircraft engines, but few survive in as good condition as the Fan Bay pair, which were excavated by the National Trust in 2014. BELOW The only surviving trace of the sound mirrors at Joss Gap, Kent, is a sawn-off brick and timber setting cut into the cliff face.
Listening carefuly Sound mirrors are much rarer than pillboxes, but were a fascinating feature of the coastal defences. These were erected from 1916 onwards and served as the forerunner to radar by providing early warning of approaching enemy aircraft. The curved surface of a large concrete dish was used to reflect sound waves from ship and aircraft engines; a cone-shaped sound collector, and later a microphone, picked up the noise. Ascertaining where on the mirror the sound was loudest determined the direction of the enemy and allowed operators to plot the path of incoming craft. Sound mirrors were installed at Kilnsea, Boulby, Redcar, Hartlepool, Seaham, and Sunderland on the north-east coast, as well as at Abbot’s Cliff, Denge, Hythe, Joss Gap, Selsey, and Sheppey in the south-east. Within 25 years, though, the higher speed of aircraft and development of radar rendered these mirrors obsolete. Few still survive.
In 2016, CITiZAN’s south-east team visited three mirror sites to establish their fate. At Joss Gap, Kent, the Signals Experimental Establishment had a remit to develop sound mirrors and other sound-detection devices until 1922. There were originally two l Trust
: Nationa image