Cryptographic History of Work on the German Naval Enigma

that the substitution made by the Grund on the first letters of the message setting was either A/J (shorthand for A encyphering as J) B/E, C/U, D/N ... or else A/P, B/V, C/D, E/X ... or else one of about a dozen other alternatives. The operator's little habits then allow us to pick out which of those alphabets is right and Banburismus can be used to fix the W.O. This is an object lesson of the danger of allowing the operator to choose his indicators. The key could be broken on this indicating system, even if indicators were genuinely random but we were very greatly helped and our work substantially reduced by having this method available for selecting the right alphabets.

3. The addition of another major key for daily breaking meant a considerable extra strain on the hut's staff. One new cryptographer, Pendered, was borrowed in August from Hut 6 - and never returned, as usually happened with such loans. The work of the crib room was not greatly increased by the change as for some time little or no cribbing was done on Porpoise; it was easy and quick to break on alphabets and there was little incentive for the cribsters.

4. The R.R. and big room were much more seriously affected. The R.R. were faced with the task of registering an additional 250 messages a day (a number which steadily increased until it reached almost 900 including Grampus, an offshoot of Porpoise) and on at least every other day the big room had to record the contents of the messages on the Banburies (punched sheets) used in the later stages of the work. Also this put a very considerable extra strain on both rooms; staff was increased as rapidly as possible but this was never a speedy process and for a considerable time everyone was very hard pressed. The girls rose to the occasion in typical style - looking back on it one is astonished at the quantity they got through and the energy and keenness shown.

5. Once we had settled down in the new routine the cryptographic work was absorbed by the section with surprising ease, largely because Banburismus and Porpoise were both intermittent jobs the "paired days" in


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