Général Araki, the Japanese Minister of War, inspects a new device for tracking aircraft by sound. The machine acted as a giant sound collector, amplifying the noise of aircraft engines and giving troops on the ground a chance to organize anti aircraft fire.
The trumpet shaped devices served to funnel the sound into an amplifier. The operator would scan the sky with the microphones trying to pick up the sound of approaching enemy aircraft.
Devices such as this represented early attempts to detect enemy aircraft before they came into visual range and were the best technology available until the development of radar. Similar devices, housed in large towers, were developed by the British after the war as a form of early warning system.
It is a testament to the speed with which warfare drives scientific and technical progress, that when the war started in 1914, airplanes were essentially a novelty. They were not armed, being used solely for reconnaissance. Soon both sides began using planes to drop bomb payloads. As these bombers became more effective, both sides developed newer and faster planes to act as interceptors. This was countered by improved bombers, and so on. As airplanes became more effective, so did anti aircraft defences. At first gunners relied on their eyesight but soon the war produced these early electronic detection and tracking devices, and, not long afterwards, radar.