Waterhouse’s billet is in the vast, makeshift camp five minutes’ walk from Bletchley Park’s Mansion. Striding briskly whilst buttoning up his shirt, he covers the distance in four. Then, twenty feet from the goal, he is nearly run over by a pack of Rolls-Royces, gliding through the night as dark and silent as U-boats. One comes so close that he can feel the heat of its engine; its muggy exhaust blows through his trouser leg and condenses on his skin.