Enigma

visit the lavatory.'
    He made his way towards the back of the hut. Kingcome and Proudfoot returned to their chess game. Atwood picked up Herodas. Baxter fiddled with his cigarette-rolling machine. Pinker closed his eyes. Jericho leafed through the Short Signal Code Book and thought of Claire.
    Midnight came and went without a sound from the North Atlantic and the tension which had been building all evening began to slacken.
    The 2 a.m. offering from the cooks of the Bletchley Park canteen was enough to make even Mrs Armstrong blanch—boiled potatoes in cheese sauce with barracuda, followed by a pudding made from two slices of bread stuck together with jam and then deep-fried in batter—and by four, the digestive effects of this, combined with the dim light in Hut 8 and the fumes from the paraffin heater, were casting a soporific pall over the naval cryptanalysts.
    Atwood was the first to succumb. His mouth dropped open and the top plate of his dentures came loose so that he made a curious clicking sound as he breathed. Pinker wrinkled his nose in disgust and went off to make a nest for himself in the corner, and soon afterwards Puck, too, fell asleep, his body bent forwards, his left cheek resting on his forearms on the table. Even Jericho, despite his determination to stand guard over the cryptograms, found himself slipping over the edge of unconsciousness. He pulled himself back a couple of times, aware of Baxter watching him, but finally he couldn't fight it any longer and he slid into a turbulent dream of drowning men whose cries sounded in his ears like the wind in the aerial farm.

Enigma
    SIX

    STRIP
    STRIP: to remove one layer of encipherment from a cryptogram which has been subjected to the process of super-encipherment (US, gv)/ i.e., a message which has been enciphered once, and then re-enciphered to provide double security.
    A Lexicon of Cryptography ('Most Secret', Bletchley Park, 1943)

1

    LATER, IT WOULD transpire that Bletchley Park knew almost everything there was to know about U-653.
    They knew she was a Type VIIc—220 feet long, 20 feet wide, with a submerged displacement of 871 tons and a surface range of 6,500 miles—and that she had been manufactured by the Howaldts Werke of Hamburg, with engines by Blohm und Voss. They knew she was eighteen months old, because they had broken the signals describing her sea-trials in the autumn of 1941. They knew she was under the command of Kapitanleutnant Gerhard Feiler. And they knew that on the night of 28 January 1943—the final night, as it happened, that Tom Jericho had spent with Claire Romilly—U-653 had slipped her moorings at the French naval port of Saint-Nazaire and had moved out under a dark and moonless sky into the Bay of Biscay to begin her sixth operational tour.
    After she had been at sea for a week, the cryptanalysts in Hut 8 broke a signal from U-boat headquarters—then still in their grand apartment building off the Bois de Boulogne in Paris—ordering U-653 to proceed on the surface to naval grid square KD 63 'AT MAXIMUM MAINTAINABLE SPEED WITHOUT REGARD TO THE THREAT FROM THE AIR'.
    On 11 February she joined ten other U-boats in a new mid-Atlantic patrol line code-named Ritter.
    Weather conditions in the North Atlantic were particularly foul in the winter of 1942-3. There were a hundred days when the U-boats reported winds topping force 7 on the Beaufort scale. Sometimes the gales reached over 100 miles per hour, whipping up waves more than 50 feet high. Snow, sleet, hail and frozen spray lashed submarines and convoys alike. One Allied ship rolled over and sank in minutes simply from the weight of ice on her superstructure.
    On 13th February, Feiler broke radio silence to report that his watch officer, one Leutnant Laudon, had been washed overboard—a blatant disregard of operational procedure on Feiler's part which brought no condolences but a terse rebuke from his controllers, broadcast to the entire submarine fleet:

    FEILER'S MESSAGE ABOUT LOSS OP WATCH OFFICER SHOULD NOT HAVE BEEN SENT UNTIL W/T SILENCE WAS BROKEN BY GENERAL CONTACT WITH ENEMY.

    It was only on the 23rd, after nearly four weeks at sea, that Feiler redeemed himself by at last making contact with a convoy. At 6 p.m. he dived to avoid an escorting destroyer, and then, when night came, rose to attack. He had at his disposal twelve torpedoes, each 23 feet long with its own electric motor, capable of running through a convoy, turning in a half circle and running