Acoustic location devices were used by military services from mid-World War I to the early years of World War II for the passive detection of approaching enemy aircraft by listening for the noise of their engines. These typically consisted of large acoustic horns attached to stethoscope-type earphones worn by monitors.The first use of this type of equipment was claimed by Commander Alfred Rawlinson of the Royal Naval Volunteer Reserve, who in the autumn of 1916 was commanding a mobile anti-aircraft battery on the east coast of England. He needed a means of locating Zeppelins during cloudy conditions and improvised an apparatus from a pair of gramophone horns mounted on a rotating pole. Several of these equipments were able to give a fairly accurate fix on the approaching airships, allowing the guns to be directed at them despite being out of sight. Although no hits were obtained by this method, Rawlinson claimed to have forced a Zeppelin to jettison its bombs on one occasion. The air-defense instruments usually consisted of large horns or microphones connected to the operators’ ears using tubing, much like a very large stethoscope.