Code Girls: The Untold Story of the American Women Code Breakers of World War II

by Liza Mundy

Before the war, a team of Polish cryptanalysts had in fact figured out the workings of the Enigma. Small, vulnerable nations surrounded by big potential enemies—Poland is bordered by Russia and Germany—tend to be hypervigilant about their neighbors, and the Polish Cipher Bureau was remarkably good. The Poles broke the Enigma during the 1930s, in part thanks to a German who passed schematics and decrypted messages to French intelligence, who passed it to them, and to a commercial model they obtained. The Polish mathematician Marian Rejewski solved the wiring, and in 1938 they built six “bomby” machines that could detect possible daily settings. In July 1939, before the Nazis overran their country, the Poles shared their discovery with the British and French. At Bletchley Park, Alan Turing and others refined the design, developing a method in which cryptanalysts could use a crib and write it beneath the cipher, then figure out, mathematically, what combination of rotor settings, wheel settings, and steckers might produce the cipher.