Before Radar Was Invented, Enemy Aircraft Were Spotted Using Sound Locators That Looked Like Musical Instruments

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.

Radar is a system where a radio signal is transmitted in a specific direction, and a receiver detects signals that bounce off any objects in the path of that signal. Because radar didn’t exist, militaries during and after World War I used a system called acoustic location. Rather than actively using generated sound to detect objects, acoustic location relied on listeners picking up any sounds or vibrations produced by the object they hope to detect. That meant they had to work very hard to try and hear noises that might otherwise be undetectable.

The outer ear, known as the pinna, is specially designed to capture and amplify sound waves, which are then funneled into the inner ear. Cupping your hand around your ear, or using an old-fashioned ear horn, enhances the pinna and amplifies sound you are trying to hear.

So, militaries experimented with many different ways of doing so. In many cases, giant horns – sometimes known as “war tubas” or “sound trumpets” – were set up so listeners on the ground could triangulate a plane’s location. Some of the horns would get its bearing, while others were used to measure its height. They would adjust the horns’ direction until the sound was loudest. Then, they would have a good idea of where the plane was.

Sound mirrors, meanwhile, were large, concrete dishes usually about 30 feet in diameter. The dish would capture the sound, and a microphone would enable a listener to hear it. While immovable, they had a much farther range than sound trumpets.

However, while all of these were innovative for their time, trumpets still only had a range of a few miles and mirrors only about 10 to 15. Both were of very limited effectiveness. This become even more true as planes got too fast for these locators.

Of course, by the time World War II started, radar was in widespread use and was much more effective than acoustic location.