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Sound
waves will reflect back from a solid surface. The direction
and magnitude of the sound can therefore be recorded and some
idea of the location of the source can be derived. Sound waves
are relatively long waves and of low energy and so they do
not travel easily over very long distances. Furthermore, they
are readily absorbed and / or deflected by objects in their
path. It was also appreciated that aircraft do generate high
volumes of
sound. It was therefore reasonable to suggest that these phenomena
might form the basis of a useful detection system.
Dr W.S.Tucker
had been given the task in 1933 (by the
War Office) of developing an acoustic early warning system
using reflectors and highly sensitive microphones at the foci.
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A number
of experimental concrete structures were built. One was a
large (200ft by 25ft) acoustic mirror built on Romney marsh.
These structures were intended to give the earliest indication
of an approaching aircraft. There were also 30ft steerable
concrete mirrors that would then indicate the target direction
by turning the dish until the maximum microphone response
was achieved.
In ideal
(very still air) conditions these devices finally managed
to achieve a maximum listening range of about 15 miles. A
bomber travelling at 220mph would cover that distance in 4
minutes! In less than ideal conditions the results were even
less impressive and the directional capabilities were non-existent.
Even noises from passing cars were enough to disrupt the detection
equipment
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To scramble
a squadron of fighters and place them strategically in the
path of an oncoming enemy squadron in under 4 minutes was
impossible and so the system was never really going to be
effective. The research did demonstrate however, that electromagnetic
wave forms could be detected, gathered and possibly measured
from a distant, unseen, and moving object.
By March 1936, it was clear that radio wavelengths could work
whereas audible wavelengths were impractical and so the project
was cancelled.
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