What was used to detect enemy aircraft

After World War II, sound-ranging played no further role in anti-aircraft operations. The Dutch personal parabola, s. This personal sound locator consists of two parabolic sections, presumably made from aluminium for lightness. They are mounted a fixed distance apart, but the size of the human head varies somewhat. To accommodate this, it appears that the instrument is fitted with inflatable ear-pads. According to a report dated , this device was put into at least limited production.

Dutch personal horns: s. This design no doubt had more gain, thanks to its greater area. It swiveled on the post behind the operator. On the right, a later version of the design on the left.

Note the extra cross-bracing added at the top of the horns. There are two counter-weights sticking out towards the rear. A Czech locator, s. Scoop-shaped reflectors direct the sound into large-diameter tubes. Manufactured by Goerz. Perrin acoustic locator on trial in France. Each of the four assemblies carries 36 small hexagonal horns, arranged in six groups of six. Presumably, this arrangement was intended to increase the gain or directionality of the instrument. The book is based on thorough research by Scarth himself as well as research conducted by British universities over the past three decades to find out how the abandoned concrete structures worked.

The targets were reached sooner and the acoustic mirrors were no longer useful. 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. Unlike the acoustic mirrors that could detect the sound of the running engine of the aircraft, the new radar technology developed in the early s used reflected radio signals. By the end of the British Air Ministry had approved the construction of an acoustic aircraft early warning system to guard the approach to London along the Thames Estuary.

The project consisted of nine giant sound mirrors and a central plotting room. This project as well was aborted due to the invention of radar, just before its construction was supposed to start in When they were taken out of service, it was suggested for them to be used as sites to experiment with explosives. However, instead of getting blown up, the mirrors were left forgotten for years.

Acoustic mirrors. To get better range, the British also experimented with a static type of sound locator, made of concrete and shaped like a dish or a curved wall, known as an "acoustic mirror. They were up to 30 feet 9 meters in diameter, but a wall-shaped one in Kent , 60 miles south-east of London, spanned feet 61 meters in length.

Many other countries including Germany, Japan and the United States were also developing sound locators at this time. Sound mirrors in Dungeness, Kent. Credit: Alamy. Obsolete, but not forgotten. After , microphones were used to pick up and amplify the noise, and later still, in , the most advanced systems did away with sound completely and transformed the noise into a visual symbol on a cathode ray tube screen -- an innovation that came from the inventor of stereophonic sound, Alan Blumlein.

The thing that overtook them, quite obviously, was the increasing speed of aircraft, which in the late s were traveling at between to miles an hour," said Judkins.