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252 SPACE, SPY SHIPS AND SCANDALS
American system - known as 'Guardrail' - proved highly effective.
19 The deploym~nt of these small sigint aircraft reflected
good previous experiences with the U-2s which had undertaken
regular perimeter sigint flights around the Eastern Bloc. 20
The biggest limitation on Britain's local ground-based sigint capability
was range of intercept. Warsaw Pact command and control
used VHF radio, and this could only be heard at a maximum
distance of forty or fifty kilometres. This reflected both transmitter
power and also the need for line-of-sight interception.
Accordingly, it was possible to provide adequate comint to divisional
commanders, but problems would occur at the level of
corps and above, which needed to see further behind the front
line. In short, sigint on Warsaw Pact reserve divisions would
have arrived too late for the commander of British forces in
Germany to react to it. Limitations of range also required sigint
collectors to be based as far forward as possible, exposing them
to risk and forcing them to move frequently, which was not
'conducive to the best COMINT collection',21 General pessimism
was reinforced by the knowledge that at the level of divisional
headquarters and above, Soviet communications security was
excellent. In 1969, the monitoring of large-scale Soviet exercises
showed that their ability to 'successfully use communications
security measures results in lean intelligence collected by
the SIGINT organisation'.22
It was only during the mid -1970s that new technology began
to provide good alternative sources. Unattended ground sensors,
small electronic devices which detected the movement of vehicles,
began to become available in Europe. Initially trialled in
Vietnam under the 'Igloo White' programme, by the early 1980s
these had become a formidable intelligence instrument. Many
of the early models - nicknamed 'bump-counters' - were tested
during real Warsaw Pact exercises in Eastern Europe, having
been put in position by Brixmis personnel. 23 Had war broken
out prior to 1970, British commanders in Germany would also
have turned to traditional air reconnaissance using aircraft with