When people generally talk about the Enigma machine, they usually imagine that it was a single model, which once the code was broken it was then possible to decrypt all of the messages that the German military sent. in fact, nothing could be further from the truth and that only adds to the amazing story of the code-breakers of Bletchley.
The history of the Enigma machine dates back to the later stages of the First World War, although it seems likely that they were still in developmental stage when the war actually came to an end. Early commercial versions became available during the 1920s and were in use by a number of governments, including that of Germany. The unique feature of the Enigma machines was that merely having a machine puts you no closer to breaking the codes of any other person who had a machine. In order to do so, you had to know the various rotor and key settings that the other person was using. It was the large variation in the settings of these rotors and keys that made Enigma such a useful tool for encryption.
An Enigma code had been broken as early as 1932 by the Polish cipher bureau. They had proved it was possible but breaking each code setting took a long time. In a previous post in this series. I discussed how prior to the outbreak of Second World War three Polish code-breakers had come to Bletchley to share their knowledge and information with their British counterparts. From 1938 onwards, the German government developed the original machine adding even more complexity to the settings and thus making it harder for anyone intercepting signals to be able to decrypt them. These developments were first tried out in the Spanish Civil War, which ran from 1936 to 1939 in which the German military supported the right wing army of Gen Franco. In 2008 28 of these Spanish machines were discovered in the attic of the Army headquarters in Madrid, where they had lain since the end of the Spanish civil war.
Even in the German military the three arms of their forces did not share Enigma machines and separate developments were used by the army, navy and air force. The Navy version of the Enigma machine, for instance, had four rotors rather than the traditional three of its compatriots increasing even further the variation that could be introduced into the cipher.
It was only the invention of pre-computers such as the bombe, which enabled the code-breakers to examine thousands of potential setting combinations in relatively quick time that shattered the unbreakability of the Enigma codes and thus allowed British Intelligence to break the codes in time to make use of the information contained in the messages. The sheer complexity of the Enigma system shines light on the genius, invention and hard toil of the code-breakers at Bletchley.