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* Home > Codes and Ciphers > Enigma
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* * * Enigma
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Catalogue reference: FO 850/234; photo of Colossus, 1943 (link to an enlarged view)
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Cracking the Enigma code
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Colossus: Eavesdropping on the German High Command
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During the Second World War German officials and military forces used an innovative electro-mechanical device known as the Enigma machine to protect their top-secret radio traffic. Though the historical documents (held at the Public Record Office) remained classified until the 1970s, the story of the breaking of the Enigma cipher is now one of the most celebrated of the war.

The Enigma machine was invented by Arthur Scherbius and produced commercially for the banking industry in 1918. The German Navy saw its potential for military use and adapted the system of rotors, keyboard and electrical wires. Resembling a typewriter, the machine was portable and ideally suited to use in combat, and was quickly adopted by all branches of the German armed forces.

Polish cryptanalysts made great strides in understanding the design of the military Enigmas and even constructed several versions of the machine. In 1939 the Germans began strengthening their system by changing the cipher every day. The German Navy equipped their Enigma machines with extra rotors and separate codebooks to create ever more complex encryptions. Enigma protected German radio communications, allowing U-boats to inflict massive losses on commercial and military shipping around Britain and the Luftwaffe to strike suddenly with devastating effect.

Throughout the war a team of British and Polish mathematicians and cryptanalysts were based at Bletchley Park (codenamed Station X), working round the clock to unscramble the streams of intercepted information. Enigma created a new form of encryption based on mathematics, not language. An understanding of letter frequency and linguistic patterns would not crack enigma encoded messages. The capture of an Enigma machine and codebooks from a German U-boat on 9 May 1941 and other more conventional acts of espionage led to significant breakthroughs.
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