Cryptographic History of Work on the German Naval Enigma

and the message trigram (Verfahren kenngruppe) and discriminant (Schluessel kenngruppe) worked out. The frequency would already have indicated that the message was on Dolphin, and the discriminant was worked out not to verify this but as a check that the indicator groups were not corrupt. (4) The message trigram was copied onto the second copy of the message which was then sent to the Hollerith section to have its contents analysed and listed for Banburismus. (5) The top copy was passed across to the typists who typed an extract from it, showing frequency, call signs, length, indicator groups and first text groups - if it was a dupe she would simply type the call sign and frequency. This register was kept in duplicate, one copy going to the crib room. The message was then passed to the Big Room, the R.R. having finished with it.

5. Having received the message the Big Room (1) checked the bigramming - it was vital that there should be no errors in this when we were Banburising and a check was therefore desirable. (2) All the clerical work involved in Banburismus was then done on the messages [See Chap IX]. This was the main function of the Big Room and occupied up to twenty people on a shift when Banburismus was at its height. If it was Porpoise message some but not all of the some processes were performed. (3) The message would then be put with other messages on the same key until the day was "broken" and the traffic could be decoded.

6. The Banburists did not handle the traffic itself at all. That worked entirely on the information produced from the traffic by (a) the Big Room (b) the Hollerith section. Most of their work was being done while the Big Room was still in the process of producing information so, when Banburising we did a large proportion of our work in the Big Room itself.

7. While this was going on the cribsters had three main jobs to perform. (1) Depth cribbing [See Chap. X]. (2) They examined the register constantly to see whether any stock cribs had appeared - recognizable by time, length, number of dupes etc. (3) They wrote on


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