Piercing the Fog - Air Force Historical Studies Office

Piercing the Fog
to assess their potential intelligence value and pass this information to
appropriate government sections and commanders.
By far the most difficult of these tasks was the first. Given the complexity
of the ciphering device the German military used for most high-grade
messages-the Enigma machine-deciphering was a daunting job. Each of the
German services used Enigma machines, but with differing keys. The British
and later the Allied teams at BP worked on all of the varied keys, only some of
which they succeeded in breaking. Not all keys that were read could be read
consistently. The German Army’s signals were most difficult for the Allied
code breakers, and those of the Lufrwuffe, the most lucrative. Ironically, it was
the seeming impossibility of breaking into the Enigma that made it such a
unique and unprecedented source of intelligence. Convinced that the system was
impenetrable, the Germans made extensive use of Enigmamachines throughout
the war, relying almost exclusively on them for the overwhelming majority of
their high-grade enciphering. Even had the Germans wanted to do so, replacing
Enigma with new machines would have been very difficult, given the large
number in use.4
The Enigma was indeed a formidable machine. Originally adapted by the
German armed forces from a commercial machine in the late 1920s and
modified several times thereafter, it operated somewhat along the lines of a
typewriter. The keys were attached to a complex system of wires, rotary wheels
(initially numbering three, with more added later), electric lights, and plugboard
connectors. As each letter was typed on the keyboard, it sent an impulse through
the machine which set rotary wheels into motion and, based on apredetermined
setting, caused a different letter to light up. To decipher the message, the
recipient had to have an identical machine, set to the proper master setting, on
which an operator would type the enciphered message in groups of five letters.
The machine would reverse the process and light up, letter by letter, with the
original message.
Although Polish cryptanalysts had begun to read Enigma messages as early
as 1933, subsequent German modifications and the variety of possible settings
meant that, as one American historian has summarized, “The breaking of the
Enigma was not a one-time feat, but an extraordinary, continuous proces~.”~
Because of the number of interchangeable wheels, the potential settings for each
one, the possible plug connections, and the variety of master settings, it has
been estimated the number of possible settings on an Enigma could have been
as high as 2.69 X loz3 for each key.6 During the war, different elements of the
German military used more than 50 separate master keys or ciphers (e.g., Red
was the general-purpose GAF code, while Garlic was the GAF weather key).’
The first decipherments were carried out painstakingly by hand with the
assistance of cribs-clues that might be revealed by the repetitious use of
certain words or phrases, or even by the style of specific operators. This
approach meant extensive delays between transmission of the original German
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