Enigma

four-rotor Enigma, multiplying the numbers by a factor of twenty-six, would theoretically take the best part of a month.
    For three weeks Jericho worked round the clock, and when he did grab an hour or two's sleep it was only to dream fitfully of drowning men. 'Let's just hope they were dead before they hit the bottom. . . 'His brain was beyond tiredness. It ached physically, like an overworked muscle. He began to suffer blackouts. These only lasted a matter of seconds but they were frightening enough. One moment he might be working in the Hut, bent over his slide-rule, and the next everything around him had blurred and jumped on, as if a film had slipped its sprockets in a projector. He managed to beg some Benzedrine off the camp doctor but that only made his mood swings worse, his frenzied highs followed by increasingly protracted lows.
    Curiously enough, the solution, when it came, had nothing to do with mathematics, and afterwards he was to reproach himself furiously for becoming too immersed in detail. If he had not been so tired, he might have stepped back and seen it earlier.
    It was a Saturday night, the second Saturday in December. At about nine o'clock Logie had sent him home. Jericho had tried to argue, but Logie had said: 'No, you're going to kill yourself if you go on at this rate, and that won't be any use to anyone, old love, especially you.' So Jericho had cycled wearily back to his digs above the pub in Shenley Church End and had crawled beneath the bedclothes. He heard last orders called downstairs, listened as the final few regulars departed and the bar was closed up. In the dead hours after midnight he lay looking at the ceiling wondering if he would ever sleep again, his mind churning like a piece of machinery he couldn't switch off.
    It had been obvious from the moment Shark had first surfaced that the only acceptable, long-term solution was to redesign the bombes to take account of the fourth rotor. But that was proving a nightmarishly slow process. If only they could somehow complete the mission Fasson and Grazier had begun so heroically and steal a Shark Enigma. That would make the redesign easier. But Shark Enigmas were the crown jewels of the German Navy. Only the U-boats had them. Only the U-boats and, of course, U-boat communication headquarters in Sainte-Assise, southeast of Paris.
    A commando raid on Sainte-Assise, perhaps? A parachute drop? He played with the image for a moment and then dismissed it. Impossible. And, in any case, useless. Even if, by some miracle, they got away with a machine, the Germans would know about it, and switch to a different system of communications. Bletchley's future rested on the Germans continuing to believe that Enigma was impregnable. Nothing could ever be done which might jeopardise that confidence. Wait a minute. Jericho sat upright. Wait a bloody minute.
    If only the U-boats and their controllers in Saint-Assise were allowed to have four-rotor Enigmas—and Bletchley knew for a fact that that was the case—how the hell were the coastal weather stations deciphering the U-boat's transmissions?
    It was a question no one had bothered to stop and ask, yet it was fundamental.
    To read a message enciphered on a four-rotor machine you had to have a four-rotor machine.
    Or did you?
    If it is true, as someone once said, that genius is 'a zigzag of lightning across the brain', then, in that instant, Jericho knew what genius was. He saw the solution lit up like a landscape before him.
    He seized his dressing gown and pulled it over his pyjamas. He grabbed his overcoat, his scarf, his socks and his boots and in less than a minute he was on his bike, wobbling down the moonlit country lane towards the Park. The stars were bright, the ground was iron-hard with frost. He felt absurdly euphoric, laughing like a madman, steering directly into the frozen puddles along the edge of the road, the ice crusts rupturing under his tyres like drum skins. Down the hill he freewheeled into Bletchley. The countryside fell away and the town spread out beneath him in the moonlight, familiarly drab and ugly but on this night beautiful, as beautiful as Prague or Paris, perched on either bank of a gleaming river of railway tracks. In the still air he could hear a train half a mile away being shunted in the sidings—the sudden, frantic chugging of a locomotive followed by a series of clanks, then a long exhalation of steam. A dog barked and set off another. He passed the church and