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Originally Posted by defcom
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Yeah, I looked there.
The one is a kenngruppenheft, which is for setting the enigma but isn't actually a 'short signal codebook', and the other has short signal-like code groups in it (the
U.Bootsabivehrsignalheft), but those appear to be for underwater signaling use using the underwater telegraphy set, something that was not generally done on an active war patrol because the 4.12 KHz audio frequency used would have been very audible to any passive sonar set in the area.