US NAVY / SCIENCE PHOTO LIBRARY US NAVY / SCIENCE PHOTO LIBRARY
Hydrophone submarine detection, World War I. British Royal Navy lieutenant operating a hydrophone listening device on board an armed trawler that is on anti-submarine patrol during World War I (1914-1918). A hydrophone is an underwater microphone, being used here to detect the sound of a submarine's engines. The headphones are being used to listen, while the microphone has been lowered into the water (lower right). For a hydrophone in use, see image C036/0820.
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