Cooke-Yarborough then moved onto the design of an
automatic radar range finder for a gyroscopic gun sight on a Hurricane
commissioned by the Royal Aircraft Establishment at Farnborough. This
would have been the first fully automated airborne radar in use, but the
project soon fell through and was replaced by an order for a warning device
for fighters. The problem was to create an early warning device for the
Army's fighter aircraft who attacked convoy lines along roads. These planes
were frequently intercepted from behind with little warning; this device
would alert the pilot when a plane was coming in from behind. Cooke-Yarborough
decided that the principle behind the range finder could be adapted and
placed in the tail end of the plane and would work just as well. His design
used a radar in the tail to give an audio signal when a plane was closing
in on the rear of the fighter. Although the device worked in trials the
Army did not use it. However the system was again adapted for use in bombers.
The restriction this time was on the parts available
to Cooke-Yarborough and the team. Due to the need to have this device
in all new bombers, and slow speed of manufactured parts, the unit was
restricted to basic, common parts. This was eventually overcome and the
Monica was born. Monica would send out a
pulse from the tail of the bomber and wait for a return signal. If no
signal was returned then no plane was within the radar's range; if a bleep
was heard over the intercom system in the bomber, then something was coming
in from behind. As the rate of the bleeps increased so the distance between
the enemy and the bomber decreased.
Cooke-Yarborough became very involved in the whole
development process of the Monica, from construction to the debriefing
of actual pilots who had used the Monica system in battle conditions,
with mixed results. One problem that the team were worried about was that
of the radar pulse acting as a homing beacon for the enemy, however the
TRE Maths division dismissed this due to the fact that for an enemy plane
to home in on the beacon it would already be within range anyway. After
the war the Maths division were to be proved wrong when it came to be
known that the Germans had done just that!
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