History tells us that the development of what we now know as radar exploded during the Second World War, with the first documented experiments dating back to the end of the 19th century. However, the technology did not arrive immediately on the battlefield, and the best alternative available to combatants was acoustic detection, with a combination of giant horns, microphones, and well-trained human ears.
The first official use of acoustic detection and location in combat was reported by Commander Sir Alfred Rawlinson of the Royal Naval Volunteer Reserve in the autumn of 1916, in charge of a mobile anti-aircraft battery on the east coast of England. In an attempt to locate Zeppelins under adverse weather conditions, Rawlinson improvised a device using the horns of two gramophones. Although he did not shoot down the enemy, the defense managed to fire in its general direction and alter its plans.
Early Acoustic Detection Systems
The development of these detection systems was not exclusive to any force, but the British stood out for the creation and deployment of acoustic mirrors, giant concrete "ears" that used movable microphones to maximize the amplitude of the received sound. By combining the records of two mirrors and applying triangulation, those in charge could determine the position of the sound.
Some systems had personal and simple designs, based on horns or "half spheres", while others were especially complex and enormous. An iconic image shows us the Japanese "war tubas", mounted on four-wheeled carriages, and the Perrin acoustic detector evaluated by France in the 1930s looks like a work of art.
The real problem with acoustic detection was that it could only anticipate an enemy attack by a few minutes, an interval that became even smaller due to the increased speed of aircraft of the time. Inevitably, the future belonged to radar, and during the period of the Battle of Britain (from July to October 1940), acoustic detection had already been relegated to a backup role.
If you have the chance to travel to England, many of its acoustic mirrors still stand (especially in Yorkshire and Kent), and can be visited by the public, with supervision.
Source: Rare Historical Photos
