Cryptographic History of Work on the German Naval Enigma

occasionally from Auka. Naval Section sent over the cribs to us after the hand cypher text had been broken. These were entered in the R.E. folders and the Enigma version was found by the girls when reading the traffic and also entered, showing the differences in the two texts. Examination of these records enabled the cribster to deal with current R.E's i.e. having received the hand cypher text they could spot the corresponding Enigma text and knew the sort of alterations that would have been made. In later days when R.E's from one Enigma key to another began to appear, the Z watch informed us of their existence i.e. when reading the traffic they spotted messages which they knew would re-encypher into another key.

19. (4) Beginner folders. These showed probable beginners of messages of given types - information that was useless for straight cribbing but of some value for depth. A typical entry would be
Frequency FromBeginnerNumber of Occurrences

These folders were entered up from the "Yellow Cards" which were cards containing typed transcriptions of the decodes of all the days messages, one message per card. Frequency, call sign, length etc. were all shown, on the card and they had a series of punched holes round the edge which could be clipped according to the features of the particular message. This having been done the cards could be immediately sorted in any way desired - all messages on the same frequency could be extracted and so on. These cards were very useful to us, particularly for any form of large scale research; their only drawback was that they reached us about five days late.

20. (5) Ship Lists. A record was kept (by frequency) of all ships which were active at any time. These lists, compiled from the yellow cards, were useful in depth cribbing. Suppose ship MMM1904 was active and in a piece of depth on a suitable frequency one threw up M....N......U....R, the MMMEINSNEUNNULVIER could be written in at once.


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