In the art of warfare, military intelligence is as important as military fire power. This is because application of force requires information on how it may be used effectively for the given situation. According to Kahn, in August 1914, the German naval codebook fell into the hands of England by way of Russian spies leading to the dramatic reduction in the effectiveness of the German Army in the North Sea[3, 972]. When the Germans discovered that the security of their system had been compromised, they took steps away from codes and codebooks toward a mechanical cipher system. This system would be known as Enigma.
Enigma is a polyalphabetic substitution cipher, or a cipher where ``the plain-text letters are enciphered differently depending upon their placement in the text.''. The mapping of the plain-text alphabet to the cipher-text alphabet is determined by a plugboard and the electrical connections between a series of rotors. For each letter encoded, the ``fast'' rotor advances one position. For each full rotation of a given rotor, the next rotor advances one position. With this setup, the alphabetic substitution changes on every letter enciphered. Furthermore, the encoding and decoding key is the initial position of the rotors. This is a mechanical codebook that, when leaked, does not compromise the security of the system. The adversary still needs the initial rotor setup.
... or so they thought.
``Franciszek Pokorny [of Poland] recognized ... what was needed to solve them [mechanized cryptosystems] was not classical scholars and philologists but mathematicians.''  So therefore he recruits mathematicians with cryptographic backgrounds who, through ineptitude on the part of the cryptosystem users, leaked information about Enigma and key mathematical insights, developed an attack that could break the security of the system. The Germans upgraded the strength of their Enigma machines by adding additional rotors, soon out-pacing the ability of the Polish mathematicians to solve for the initial rotor configuration. The information on Enigma as well as the code-breaking techniques and machines were passed on to France and England, with the English ultimately taking the final steps to break the full five rotor system within reasonable time constraints.
Even though World War II had come to a conclusion, the secrecy surrounding breaking enigma survived for another thirty years, until 1974, when England approved release of the information in the form of a book titled, The Ultra Secret. According to Kahn, this secrecy served the purpose of protecting the Enigma user-base, such as former colonies, which had been provided with Enigma machines to secure their communications. The more cynical view is that the England benefited from the continued use of a broken cryptosystem.