Before radar, people developed devices that directly listened to sounds emitted from a distance to detect enemy aircraft.
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| The “two-horn” listening system, installed at Bolling, Field, USA, in 1921. |
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| German sound positioning technology in 1917. When sound is located, the glasses will help to see the plane clearly. |
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| Dutch personal parabola of the 1930s, made from aluminum for lightness. |
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| In this version (also Dutch), there is an additional rubber cushion at the ear of the operator. |
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| Czech positioning device. The sound collector will direct the sound into large diameter tubes leading to the listener's ears. |
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| Perrin’s acoustic device was tested in France. The device consisted of many “antennas” to capture as much sound as possible to help locate enemy aircraft. |
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| Directional listening device developed by Germans in 1915. |
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| Three Japanese sonar devices, mounted on four-wheeled carts. In the photo, Emperor Hirohito is inspecting the devices./. |
According to VOV
