The British escape map of the Second World War was printed on silk because paper got men shot. The man who designed it was Christopher Clayton Hutton, a First World War pilot and amateur magician who talked his way into MI9, the department whose only job was getting captured servicemen home. He read 50 Great War escape stories before he started, and the thing that came up in all of them was the map. A paper map fails in every way that matters to a man on the run. It rustles when a guard pats him down. It tears along the folds. It turns to pulp in the first ditch he lies in. And it is too stiff to hide anywhere a search will not find. So Hutton went to the one firm in Britain that could print on silk, which happened to be Waddingtons, who also held the Monopoly licence, and the maps went out folded into the pieces of a board game sent to the camps through fake charities. Others went into cigarette packets, hollow boot heels, and the lining of a flying jacket. Silk is a protein spun by a caterpillar. It is stronger for its weight than steel wire, it folds a thousand times without a crack, it dries in minutes, and it makes no sound. Nothing in the chemical industry of 1940 could do all four, and the rayon they tried when the silk ran short was never as good. Around 400,000 cloth maps were printed. The historians put the men who got home with Hutton's kit in the tens of thousands. The spy gadget that freed more prisoners than any other in the war was a handkerchief, and the handkerchief was made by a worm.