The History of Hut Eight

tionship to HIJ - 1 alphabet plus 1 letter, or 2 plus 1 letter etc. and, inasmuch as HOD is long enough, we can try these possibilities also. Although the whole message cannot be cribbed the position illustrated where I = O + 3 on the Middle wheel is clearly right, all the consequences are good letters and at one place much of IENSNULYYEINSNUL is thrown up. HOS can then be attached.

It would be pointless to pursue this depth further. More might well be added and, once started, the messages might be read for some distance. The delight of depth lay in its great variety - no two depths were ever quite the same - and it were a blase cryptographer indeed who experienced no thrill at discovering a right position and correctly guessing large chunks of message about the contents of which he at first knew nothing. Needless to say things rarely went as smoothly as in our example and it was possible to work for a very long time without even getting a piece of depth started.

There were other applications of depth cribbing of which only one need be mentioned here - the slide. The slide is similar to the process by which we started our last example but in this case we only have a crib for one message - a fairly long and probably a right crib. If SWI is our cribbed message, we examine the consequences of trying SWL for 25 places to either side of it and, although we cannot attempt to crib result,


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