Codes and Ciphers: Radio Communication and Intelligence
From the outset of World War II, radio communications were crucial to both sides in the conflict. Both sides used codes and ciphers to protect these communications, and both were successful in their efforts to gain intelligence out of the enemy's communications by some form of radio or signal intelligence. The French Navy used as its main cipher, in addition to some other not so important systems, the "Touts Batiments Militaires," a five-digit code which was super-enciphered up to the beginning of the war with numeral exchange tables. The well-known Bismarck operation was tactically influenced by radio intelligence almost exclusively by traffic analysis and direction finding. Admiral Dönitz pressed for a separation of the U-boat radio traffic from the surface traffic and tried to introduce other security measures, including ordering by a code word the change of the cipher settings.