No Concrete … Radar and Sir Robert Watson-Watt

Scottish physicist Sir Robert Watson-Watt invented the first practical radar system back in 1935. The system used pulsed radio waves, and it could detect airplanes up to 100 miles away.

A few years later, a chain of radar stations were established throughout England, which helped defend the British and 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 knighted for it in 1942.

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

Concrete Acoustic Mirrors and How They Worked

The MASSIVE CONCRETE ACOUSTIC MIRRORS, or “listening ears,” lining the southeast coast of England were built between the world wars to monitor the skies for the tell-tale sounds of airborne invasion.

Constructed between 1927 and 1930, the sound mirrors were part of Britain’s national defence strategy. Their parabolic shape collected and magnified sound waves in the air over the English Channel and directed them at a microphone positioned just in front of the parabola. Anti-aircraft defences were then deployed. The mirrors effectively gave Britain a 15-minute warning of an impending attack.

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.

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.

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 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.

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.

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