Enigma

always began its reports in the same way:
    WEUBYYNULLSEQSNULLNULL
    ('Weather survey 0600', WEUB being an abbreviation for WETTERUBERSICHT and SEQS for SECHS; YY and NULL being inserted to baffle eavesdroppers).
    The cryptanalyst would lay out the ciphertext and slide the crib beneath it and on the principle that nothing is ever itself he would keep sliding it until he found a position in which there were no matching letters between the top and bottom lines. The result in this case would be:
    BSTUXNTXEYLKPEAZZNSKUF
    WEUBYYNULLSEQSNULLNULL
    And at this point it became theoretically possible to calculate the original Enigma settings that alone could have produced this precise sequence of letter pairings. It was still an immense calculation, one which would have taken a team of human beings several weeks. The Germans assumed, rightly, that whatever intelligence might be gained would be too old to be of use. But Bletchley—and this was what the Germans had never reckoned on—Bletchley didn't use human beings. It used bombes. For the first time in history, a cipher mass-manufactured by machine was being broken by machine.
    Who needed spies now? What need now of secret inks and dead-letter drops and midnight assignations in curtained wagons-lits? Now you needed mathematicians and engineers with oilcans and fifteen hundred filing clerks to process five thousand secret messages a day. They had taken espionage into the machine age.
    But none of this was of much help to Jericho in breaking Shark.
    Shark defied every tool he could bring to bear on it. For a start, there were almost no cribs. In the case of a surface Enigma key, if Hut 8 ran out of cribs, they had tricks to get round it—'gardening', for example. 'Gardening' was arranging for the RAF to lay mines in a particular naval grid square outside a German harbour. An hour later, you could guarantee, the harbour master, with Teutonic efficiency, would send a message using that day's Enigma settings, warning ships to beware of mines in naval grid square such-and-such. The signal would be intercepted, flashed to Hut 8, and give them their missing crib.
    But you couldn't do that with Shark and Jericho could make only the vaguest guesses at the contents of the cryptograms. There were eight long messages originating from Berlin. They would be orders, he supposed, probably directing the U-boats into 'wolf packs' and stationing them in front of the oncoming convoys. The shorter signals—there were a hundred and twenty-two, which Jericho sorted into a separate pile—had been sent by the submarines themselves. These could contain anything: reports of ships sunk and of engine trouble; details of survivors floating in the water and of crewmen washed overboard; requests for spare parts and fresh orders. Shortest of all were the U-boats' weather messages or, very occasionally, contact reports: 'Convoy in naval grid square BE9533 course 70 degrees speed 9 knots . . .' But these were encoded, like the weather bulletins, with one letter of the alphabet substituting for each piece of information. And then they were enciphered in Shark.
    He tapped his pencil against the desk. Puck was quite right. There was not enough material to work with.
    And even if there had been, there was still the wretched fourth rotor on the Shark Enigma, the innovation that made U-boat messages twenty-six times more difficult to break than those of surface ships. One hundred and fifty million million million multiplied by twenty-six. A phenomenal number. The engineers had been struggling for a year to develop a four-rotor bombe—but still, apparently, without success. It seemed to be just that one step beyond their technical ability.
    No cribs, no bombes. Hopeless.
    Hours passed during which Jericho tried every trick he could think of to prompt some fresh inspiration. He arranged the cryptograms chronologically. Then he arranged them by length. Then he sorted them by frequency. He doodled on the pile of paper. He prowled around the hut, oblivious now to who was looking at him and who wasn't. This was what it had been like for ten interminable months last year. No wonder he had gone mad. The chorus-lines of meaningless letters danced before his eyes. But they were not meaningless. They were loaded with the most vital meaning imaginable, if only he could find it. But where was the pattern? Where was the pattern? Where was the pattern?
    It was the practice on the night shift at about four o'clock in the morning