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.

Slidex encoding/decoding card.  As an example, using the card and keys set in the photo, the order to "Change Frequency At Once" would be encoded as "AV EB TM". (Photo by Jerry Proc) 

A better photo of the code pad. (Photo source unknown)

Slidex training. (A photo of a photo taken by Jerry Proc).

Complete kit
Coding sheet placement in holder. 
Instruction manual 
Additional coding sheets
Carrying case
All photos in this table courtesy E-bay.


Contributors and Credits:

1) Gary Jones <hjhagermann(at)>
2) Source:  Bloody Sunday Enquiry

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Jan 11/10