From the Electronic Telegraph in London...
 KENNETH Johnston, who has died aged 92, played a central role in
 safeguarding the security of RAF signals during the Second World War.
 Johnston was 34 when the war broke out, and normally would not been
 called up for two years. However, he volunteered for Naval Intelli-
 gence and, after a short stint in the cyphering section at the Ad-
 miralty, was appointed Signals Security Officer at the Air Ministry,
 with the rank of Squadron Leader.
     Johnston gradually acquired assistants at the Air Ministry and
 at the Commands. Later, he had representatives in Washington, the
 Middle East and with the invading force in France.
     One of his tasks was to avoid the appearance of anything extra-
 ordinary before an important Allied offensive. When, for instance,
 the Allies prepared to invade North Africa, it was clear that prep-
 arations for this would mean a marked increase in signal traffic to
 Gibraltar, particularly in high priority messages.
     "Fortunately, the cable to Gibraltar was not cut," Johnson later
 recalled, "and I put a man at the main RAF wireless station, with
 the task of diverting traffic to cable to avoid the appearance of
 anything exceptional in the signal traffic sent by wireless."
     After a year or so, Johnston was promoted Wing Commander and put
 in charge of RAF cyphers and codes. He was responsible for the
 distribution of cypher machines and for instructions as to their
 use.
     As the German Enigma code began to be broken at Bletchley Park,
 Johnston was continually asked to improve his own machines and the
 methods of their use.
     His work was not without its alarms. Malta was very isolated for
 a long period during the war, and Johnston's cypher machines had to
 be supplied either by fast minelayer or by flying boat from Egypt.
     One flying boat was forced down off the North African coast. The
 crew jettisoned the cardboard boxes containing the cypher machines
 and then got into a rubber dinghy. But as they rowed ashore, with
 the boxes floating alongside them, they were captured by Italian
 soldiers.
     North Africa was cold at that time of year, and the RAF crew
 suggested that the handy cardboard boxes be used to make a fire.
 Their Italian captors joined in enthusiastically. When the crew
 explained that the box with the secret cypher drums contained only
 an old camera, it was consigned to the flames.
     Johnston twice travelled to Washington to discuss mutual signal
 security concerns. On the second occasion, in 1944, he attended the
 meeting in the Pentagon at which the expression "Top Secret" was
 first devised. It was a way of describing the most secret category
 of war documents in a way that was acceptable both to the Americans
 and to the British, who had previously used the term "Most Secret".
 Ray Marsh, Brisbane, Australia.        raymarsh@hotmail.com
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