Originally, acoustic location was used for ship detection in fog conditions but from mid-World-War-One to the early years of World War Two the devices were often used for aircraft detection. They were all rendered obsolete by the introduction of radar, but for a time they served a useful purpose in national defense.
If not effective they were at least distinctive. At the Brussels Inventor's Fair of 1960, Frenchman Jean Ausgher exhibited his wearable acoustic navigation device. It was to be used by small ships in case of radar failure. The distance between the horns increased the observer's ability to localize the direction of a sound. Unfortunately, in this case the horns weren't far enough apart. With Ausgher's device you would hear an oncoming vessel about the time it was to collide with you.
No detector was better than the German Ringtrichterrichtungshoerer (RRH). The detector was used mainly in anti-aircraft searchlight batteries for the detection of British night bomber formations. The RRH could detect targets at a distance of twelve kilometers, and depending upon weather conditions and operator skill, it could help detect the size of the aircraft formation. It had a directional accuracy of 2 degrees. The device had a crew of three with the dial reader in the middle. The rolled up material over the operator's heads could be unfurled to provide cover in bad weather.
The British and Americans also had small acoustic detectors of limited effectiveness. However, the British did build a series of huge stationary concrete "acoustic mirrors", some of which are still standing to this day.
Another remarkable machine was a French acoustic locator based on a hexagonal layout. Each of the four assemblies carried thirty-six smaller, hexagonally-shaped horns. This layout was presumably used to increase the directional gain of the equipment. Because the detector was so large and out in the open, the type was abandoned after being repeatedly bombed by the enemy.