ple, and get the code book with the daily settings for the next month. The alternative method - which was The Enigma machines were deliv- adopted during the greater part of ered to the Army, the Navy and the the war - was to transmit the day’s German Air Force, and operated even configurations as a preamble to in the railways and other depart- the daily messages themselves, but ments of the government. As was coded according to the configurathe case with all the code systems tions of the previous day. that were used during this period When the war started the British of time, a weakness of the Enigma was that the receiver had to know School of Codification was domithe configuration set by the issuer. nated by linguists and scholars of To preserve the security of Enigma, classical languages. But the Ministry settings had to be altered every day. of Foreign Affairs soon realized that One of the ways that the issuers had their theoreticians of numbers had to change the configurations with a higher probability of finding the frequency and keep the receivers key to break the German codes i n f o r m e d and, to begin the operation, nine was the of the most brilliant British theop u b l i c a - rists of numbers were gathered at tion of the the new headquarters of a school daily con- in Bletchley Park; a Victorian manfigurations sion in Bletchley, Buckinghamshire. in a book One of them of course was Turing of secret who had to abandon his hypotheticodes. The cal machines with tape and infirisk of this nite unlimited processing time; to m e t h o d face a practical problem with finite was that resources and a very real time limit. the British In fact, the Enigma had to be brocould capture a ken afresh over and over again. G e r m a n The brilliant pre-war work by Polish submarine, mathematicians, which enabled the for exam- reading of Enigma messages on the sent twice, but are encoded differently each time. 34