Before the invention of radar during World War II, incoming enemy aircraft were spotted using "sound locators" that looked more like musical instruments than tools of war.
Before the invention of radar during World War II, incoming enemy warplanes were detected by listening with the aid of "sound locators" that looked more like musical instruments than tools of war.
These radar forerunners, which earned the nicknames "war tubas" or "sound trumpets," were first used during World War I by France and Britain to spot German Zeppelin airships. Essentially, the purely mechanical devices were large horns connected to a stethoscope.
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"It was a development of artillery sound ranging," explained Phil Judkins, a war historian and Visiting Fellow at the University of Leeds, during a phone interview.
"It had been noticed for quite some time that you could locate a gun if two or three or four different people listening to the gunshot each took a bearing." Combining the bearings or the measurements of direction between two points would give the gun's location. That same process was then applied to listening for aircraft.
A common configuration of the device had three horns arranged vertically plus an extra one to the side. The central one in the set of three and the lateral one were used to get the aircraft's bearing, while the remaining two were used to estimate its height. The operators would listen in through the stethoscope and tilt the horns until they got the loudest sound.
"That will then give you the direction, and with a little trigonometry, it will give you the aircraft's height," said Judkins.
Sound locators were used near the frontline in conjunction with anti-aircraft guns, but their range was limited to just a few miles. "The number of times any enemy aircraft was actually shot down using them is very small, or at least the number of recorded occasions that we know about. But the number of times any enemy aircraft was shot down using fighters and so on was pretty small as well," said Junkins.