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ColossusThe secrets of Bletchley Park's code-breaking computers$
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B. Jack Copeland

Print publication date: 2006

Print ISBN-13: 9780192840554

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780192840554.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 17 June 2021

D-Day at Bletchley Park

D-Day at Bletchley Park

(p.78) chapter 6 D-Day at Bletchley Park

Thomas H. Flowers

Oxford University Press

Before the war in Europe started in 1939, I worked as an engineer in the Dollis Hill communications research laboratories of what was then the British Post Office and is now British Telecom. During the war I continued to work in the laboratories; luckily I was not conscripted into the armed forces. Early in 1942 I was directed to go to GCHQ, the Government Communications Headquarters, then at Bletchley Park. I was told that there I would be briefed concerning some top-secret work which they wanted our laboratories to do for them. At Bletchley Park I met Alan Turing. Turing was working on Enigma at that time, and it was he who wanted the top-secret work done—a machine to assist with decoding Enigma messages once the Bombe had produced the message settings. From then until the end of the war, I was a frequent visitor to GCHQ. In the early years of the war, Alan Turing had saved Britain from defeat by the U-boats, by breaking the Enigma code used by the German Navy to communicate by radio with their ships at sea. Radio broadcasting is the only possible way of maintaining contact with mobile units like ships, tanks, and troops, but it is not secret—the transmissions can be intercepted by anyone with a suitable radio receiver. Therefore the messages must be encrypted before transmission. Even then the transmissions are secure only so long as the code remains unbroken by the enemy. The Germans were very sure that their high-grade ciphers could not be broken! British intelligence services had many radio receiving stations at home and abroad, listening continuously to German military radio broadcasts. These stations sent the coded messages they intercepted to Bletchley Park. In 1940 Bletchley Park started to receive teleprinter messages in a code that they could not recognise. The Germans had invented a new coding machine specifically for teleprinter messages. Messages typed into this machine in plain language were automatically encoded before being transmitted. At the receiving end an identical machine automatically decoded the message and printed the plaintext on paper tape.

Keywords:   Analyser (decoding machine), Bombe, D-day, Post Office Research Station at Dollis Hill

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