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Regarding the second paragraph of the introduction.
SLIDEX was a cypher system using bigrams to encrypt the plain text. It was broken by the Germans in WWII and thereafter by anyone listening in on the net with time on their hands.
BATCO was a one time pad system where a numerical code was used to encrypt the plain text. Once used the numerical code should not be reused. As with all one time pads they cannot be decrypted unless the pads have been compromised or codes reused.
So BATCO replaced SLIDEX but was not similar. BATCO required printed BATCO pads of sheets to be distributed, whilst the SLIDEX Alphabets could be set at unit level.
