How did this ugly concrete lump on Kent’s coast help to defend the capital?
This concrete dish was once part of Britain’s national defence strategy. Known as ‘sound mirrors’ or ‘listening ears’, objects like this were used during the First World War and beyond to detect enemy aircraft.
Notice the bowl-shaped hole scooped out of the centre. This concave shape was deliberately designed to ‘catch’ sound waves coming from approaching planes. The sound waves were then relayed back through microphones to an operator, who could raise the alarm. This gave the military a fifteen-minute warning and time to organise their anti-aircraft defences.
Several sound mirrors were built along England’s east coast - in Kent, Yorkshire and Durham - to detect airborne threats from across the Channel and North Sea. The one here at Abbot’s Cliff, built in 1928, is one of seven in Kent alone, strategically positioned to detect aircraft aiming to attack London.
The system was never really successful however. Weather conditions affected how the sound waves were detected. Developments in aircraft design meant faster planes would already be too close for the ‘ears’ to hear them. In 1939, the invention of radar effectively drowned out the listening ears.
Now abandoned, they still stand sentinel along our coast. These days they attract the attention of psychogeographers and military historians. Fashion photographers use them as the backdrop for their shoots and bands including Turin Brakes, have featured them on their album covers.
The Folkestone acoustic mirror also features in wartime artist Eric Ravilious’ 1941 watercolour Bombing the Channel Ports.
Written by Caroline Millar, Discovering Britain Project Manager, RGS-IBG