[an error occurred while processing this directive] World War II Encryption:
By World War II, encryption had evolved to a much more modern system than codebooks and pencil-and-paper ciphers. The mechanical machine had begun to enter the arena. This progression allowed for messages to be created with much stronger encryption, and to be cracked with much more efficiency. Thus, it is left to philosophy if anything really changed.
The mechanical machines of the time operated by using rotors, devices that contain wires cross-connecting letters of the alphabet, so that one letter is substituted for a different one. What made rotors more powerful than a simple substitution cipher, though, was that the "rotors" rotate with each letter encrypted with the machine, so that the system used to encipher a letter changed with each additional one.
Every written system of encoding was broken during World War II, with a single exception. The rotor machine that the allies used, known by the acronym SIGABA, remained unbroken for the duration of the war.
More Topics on World War II Encryption:
The German Enigma Machine (and simulator)
How the Allies Cracked Enigma (Bombe, and simulator)
The Japanese PURPLE encryption system
The Allies' Crack-Proof system, SIGABA (and simulator)
Role of the Navajo Indians as Codetalkers