Before Radar, they used these giant concrete “Sound Mirrors” to detect incoming enemy aircraft

Goran Blazeski
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Photo Credit John Poyser CC BY- SA 2.0

Many historians agree that spotting enemy airplanes, ships, or submarines, was what clearly made the difference in World War II, with some of them even adding that the radar didn’t just revolutionize air and naval warfare, but more importantly, it won the war for the Allies. This early warning system was a vital factor in the RAF’s triumph in the Battle of Britain and had a decisive effect on the course, and later, on the outcome of World War II.

Using aircraft in warfare was not a new concept towards the end of the 1930s when World War II began. The Germans used giant Zeppelins and bombed the capital of England for the first time some 20 years ago when the Great War ravaged Europe.

Scottish physicist Sir Robert Watson-Watt, who was not just a brilliant individual in his own right, but also one of the people who inevitably defined the outcome of World War II by inventing the first practical radar system back in 1935.

The system used pulsed radio waves, and it could detect airplanes up to 100 miles away, but most importantly it saved thousands of lives. What he has accomplished over 80 years ago was truly groundbreaking and it is something that is still in use today.

A few years later, a chain of radar stations was established throughout England, which helped defend the British and as mentioned above it played a crucial role in the Allied victory in World War II. It was a huge discovery and the inventor Sir Robert Watson-Watt was knitted for it in 1942.

But what about the period before the radar was invented? What was the forerunner of radar and how the British defended themselves from the German Zeppelins during World War I?

Acoustic mirrors at Denge. Author: Paul Russon  CC BY-SA 2.0


4.5 meter high (14ft 9in) WW1 concrete acoustic mirror near Kilnsea Grange, East Yorkshire, UK. Author: Peter Church  CC BY-SA 2.0

Dr. William Sansome Tucker developed early warning systems known as ‘acoustic mirrors’ in around 1915, and up until 1935, Britain built a series of concrete acoustic mirrors around its coasts. The acoustic mirror was the forerunner of radar, and it was invented to help detect zeppelins and other enemy aircraft by the sound of their engines.

The British used these devices and with their help, they managed to detect many enemy raids. The acoustic mirrors could detect an incoming aircraft up to 15 miles away, which gave English artillery just enough time to prepare for the attack of the German bombers.

Kent acoustic mirror.Author: Mark Duncan  CC BY-SA 2.0


The farmland has been ploughed around the mirror. The rusty pole in front of the mirror had a microphone attached to it when listening for aircraft in the First World War. Author: John Poyser CC BY-SA 2.0


Round acoustic mirror in Denge, Kent, England, 19 July 2009. Author: Bodacea   CC BY-SA2.0

Many of these strange looking devices remain on Britain’s coastlines, more or less intact. They can be seen in many places throughout the country, including Hartlepool, Seaham, Redcar, Sunderland, Dover, Romney Marsh and Selsea. However, some of the finest examples of acoustic mirrors can be seen on the Dungeness peninsula and at Hythe in Kent.

On the former Royal Air Force site near Dungeness, in Kent, England, there are three acoustic mirrors built between the 1920s–1930s; one of them is a 70m (230 ft) curved wall, around 5m high, while the other two are dish-shaped around 5m in diameter.

Sound Mirrors at Denge. Author: Hywel Williams  CC BY -SA 2.0

Hot-wire microphones designed personally by Dr. William Sansome Tucker that were placed at the focus of each structure made it possible for the listeners to detect the sound of an oncoming enemy aircraft and gave a fifteen-minute warning to the English artillery to prepare for the attack. Some of the most sophisticated acoustic mirrors could detect the sounds of oncoming enemy aircraft up to 25 miles (40km) away.

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As aircraft performance increased, its sound could no longer be heard or located 15 minutes before it reached its target, and that is why acoustic mirrors were no longer useful and were replaced by the newly developed radar technology.