Before the development of radar, military personnel relied on various methods to detect and track incoming enemy aircraft.

One such method involved utilizing "sound finders," also known as acoustic locators. These devices, which resembled large funnels or megaphones, were positioned strategically to intercept the sound waves emitted by approaching airplanes. There were even portable versions.

Sound finders worked by employing the principle of triangulation. By analyzing the subtle differences in the sound reaching each of the device's two or three horns, operators could pinpoint the approximate direction of the sound source. The closer the aircraft was, the more pronounced the difference in sound intensity between the horns. This information was then relayed to anti-aircraft batteries, allowing them to anticipate the enemy's approach and prepare their defenses.

Sound finders were initially deployed during World War I, particularly in the early stages of aerial warfare. While they provided valuable information about the enemy's position, they were not without their limitations. Their effectiveness was hampered by factors such as atmospheric conditions, background noise, and the complexity of interpreting the subtle sound variations. Additionally, sound finders were primarily suitable for detecting low-flying aircraft, as higher-flying planes were more difficult to discern against the background noise.

The advent of the first practical radar systems sent the sound finder into the oblivion and what we have is mostly photos depicting that short stretch of time.