Slidex was a manual encoding system used to provide a short
term level of security when non-secure communication links were being used.
Gary Jones provides some background information on the device. "This
was introduced into the British Army circa 1943/44, and by virtue of radio
monitoring was broken by the German Intelligence fairly rapidly.
In spite of that, it soldiered on until at least the early 1980's since
it's mentioned as having been used by the Parachute Regiment on active
duty in Northern Ireland [2] . I used it as a radio operator in the 1960's
and 1970's, in both a regular Army and reserve capacity. The system
relied on the card, each of which was specific to arm, and the plastic
cursors which were one vertical on the left and one horizontal on the top.
If memory serves, the first 4 spaces had 2 letters and were used to set
up the code pad, much as a map reference is used. Each square had
phrases which were specific to arm, and letters which could be used to
spell out messages. (TIME CONSUMING!) Interestingly the East German
Armed Forces had a similar device which they called "SPRECHTAFELN" (Talking
Tables) which worked on an identical principle. And they, would you believe,
got it from the Soviets!"
SLIDEX was apparently adopted for use by all the units involved in
Operation OVERLORD. All cards issued prior to 1970 are no longer classified.
