[Milsurplus] Crypto for TTY 131B2 ?

[Hubert Miller]

Manual for the 'Teletypewriter Set 131B2" says accompanying crypto equipment
is "black metal box referred to as crypto unit"

or a "SpTD unit", Special Transmitter-Distributor, which units scramble or
descramble the teletype characters passed thru them

to the 131B2.  

 

What are the type numbers of these crypto equipments and has anyone seen the
manuals for them? I'd like to know more about

how they based their scrambling method.

-Hue Miller 

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