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.
