Listening for the Enemy Giant Ears on the British Coast
Part 2: Mega-Mirror Delivering Results
Tucker then installed microphones in concreted areas in front of the acoustic baffles, as well as switches and lights which were connected to the control room. Personnel were thus able to determine which microphone received the strongest signal, and give the listening post advice on where to look. The identified site in turn passed the position of the aircraft on to the control room once it had been calculated.
With a range of about 20 miles, the mega-mirror finally delivered the required results -- and at the Air Ministry, the plan matured into a huge project: a chain of 45 of the 60-meter sound mirrors supplemented by 60 of the nine-meter-high mirrors to be built along the coast from the county of Norfolk above the Thames estuary down to Dorset in the southwest of England, to make it impossible for enemy planes to approach the UK from the English Channel undetected.
In the summer of 1932, the Royal Air Force began training personnel in the use of the Hythe sound mirrors. Work on the stethoscope required extreme patience, endurance and concentration. In addition, it was necessary to train staff for the rapid and accurate communications required between the listening post, telephone operators and officers in the control room and at headquarters.
Troublesome Background Noise
Tucker and his colleagues used annual military maneuvers to refine their instruments. The microphone system had to keep pace with the rapid development in aircraft technology, and it needed to be sensitive to different sounds and different engines. In addition, airplanes were becoming faster. Adding to the problems was increasingly troublesome background noise from urban development and road traffic, which even the idyllic Hythe was not spared.
By the end of January 1935, the greatest doubts seemed to have been dispelled. Top Royal Engineer officials ordered a detailed plan from Tucker for the necessary communications systems, mainly telephone lines and exchanges. By June of that year, the Air Ministry employed more than 500 people on the sound mirror project -- a figure that revealed the high priority of the early warning system.
But a letter from the Ministry in August abruptly brought the plans at the research station to a halt. Work was at first temporarily suspended until the end of September, upon which a further delay was implemented -- justified by the development of alternative detection methods.
In fact, by September 1935 the alternative had already been found. Scottish physicist Robert Watson-Watt had been experimenting with radio waves for years, and had recently used them for wireless communication with pilots. Now he could report further technical progress: By transmitting radio waves which were reflected back down to the ground station by the aircraft, a plane -- and thus a potential enemy -- could be located without any help from its crew. The new technique was dubbed Radio Detection and Ranging, or radar for short. It would eventually go on to play a significant role in the defense of Great Britain during World War II, and would become the fundamental component of every modern air defense. The concave mirror system had outlived its usefulness.
Tucker and his colleagues nonetheless continued their work at the Hythe research station until the end of the decade. It wasn't until 1939 that senior officers of the Royal Engineers decided to give up the sound mirror idea for good. The mirrors in existence were due to be destroyed. At the same time, Tucker had started his last year as director of the research center. He found it difficult to be separated from his scientific work, and he asked the War Department to extend his service -- but in vain.
In February 1940, his employment ended. But the plan to destroy the mirrors was never executed. Although one of the six-meter-tall sound mirrors at Hythe simply fell over during the 1980s, the rest have remained intact as bizarre relics of an almost-forgotten technology.
This article originally appeared in German on einestages.de, SPIEGEL ONLINE's history portal.
- Part 1: Giant Ears on the British Coast
- Part 2: Mega-Mirror Delivering Results