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Dissemination

The final step in the codebreaking process was to send the resulting top secret...

… intelligence to the relevant people. Bletchlety Park turned the analysed information into intelligence reports and passed them on – the Codebreakers themselves did not decide how to act on them. Intelligence from complex ciphers such as Enigma was codenamed Ultra. To prevent the enemy finding out their ciphers had been broken, BP’s reports were often made to look as if they had come from spies working abroad. Material was passed to MI6 but also direct to the Admiralty, the War Office or the Air Ministry, and to some commands depending on the content of the reports.

Special Liaison Units and their associated communications specialists, the Special Communication Units, were also set up to feed the Bletchley Park intelligence to commanders in the field, first briefly in France in May 1940 and then in North Africa and elsewhere from March 1941 onwards.

Based at military command posts around the world, these units received the Ultra reports from MI6 via secure links which used either the British Typex cipher machine or one-time pad cipher. Officers from the Special Liaison Units then passed the intelligence directly to the commanders to ensure the Ultra secret was protected.

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