Undisclosed location in Japan.
Photographer: Unknown
Accompanied by high ranking officers with Samurai swords held rigid at the side, Japanese emperor Michinomiya Hirohito inspects a line-up of Type 90 sound locators on trolleys, in an undisclosed location in Japan, 1930.
Prior to the invention of the radar in 1935, many armies across the world had relied on one or another form of this acoustic device to search out enemy aeroplanes in the dark when look-outs in their observation posts were of little or no assistance at all.
A natural evolution of the ear horn that is attested to have been in use as a hearing aid since the 17th century. Sound locators had largely come into service during World War I as part of an army’s anti-aircraft arsenal and continued even during World World II – especially in the case of Japan that had lagged behind the west in technological advancements.
Though different countries had developed these devices as per their own research and specifications, most models had usually comprised of four trumpets attached to two stethoscope like hearing tubes, and had required a team of three or more to operate.
While one person using the hearing tube attached to the first pair of trumpets had gauged the altitude on an incoming aeroplane. The second using the other hearing tube attached to the second pair of trumpets had calculated the distance. This, while the third member, using an instrument attached on the locator itself, had kept track of the direction in which the device was pointing at any given time.
The Japanese Type 90 that Hirohito can be seen inspecting in the photo was developed in 1930. Out of the two versions produced at the time. One was of a larger make possibly for use in military bases or cities while the other was smaller in size and meant for use in the field.
Like other devices of its kind with other armies, the Type 90 was originally designed to assist anti-aircraft guns on its own.
However, after field tests had revealed its ineffectiveness in accurately pinpointing the location of incoming aeroplanes, largely for the amount of calculations required and the factors involved such as wind velocity, air density and humidity that affects the speed of sound, it had been reassigned to assist searchlight crews.
This new role had required it to simply indicate the direction of the coming aeroplane for the searchlights to illuminate it and the anti-aircraft guns to bring it down.
