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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: 13 June 2021

Major Tester’s Section

Major Tester’s Section

Chapter 18 Major Tester’s Section

Jerry Roberts

Oxford University Press

Tunny messages passed primarily between army headquarters in Germany and the various army groups. A great deal of traffic passed between headquarters and Army Group B, where the main fighting on the Western front was concentrated. On the Eastern front, messages between headquarters and Army Groups North, Central, and South dominated the traffic. Many messages were signed by top field marshals like von Rundstedt, Model, Rommel, and Keitel. Occasionally there were messages signed by Hitler himself. Tunny provided information about the Germans’ actions and planning from the spring of 1942 onwards—from the time of Hitler’s decision to focus on the Russian front through to the final breakthrough of the Allied armies in 1945. The strategic value of the information was immense. One long message alone gave the whole disposition of the units within the army groups on the Eastern front, and, within each army, of the divisions, panzer-divisions, and all the other specialised units. Our problem was how to convey the gist of this information to the Russians without letting them know how we had derived it. In June 1944 Hitler assembled the main body of his troops in the Pas de Calais, well north of the Allied landing beaches in Normandy, believing that the main Allied attack would come in the Calais region. If, instead, Hitler had committed these troops straight after the Normandy landings and thrown the Allied forces back into the sea, the consequences would have been incalculable. That he did not plan to do so was known through the decryption of Tunny. This is only one example of the many crucial contributions that Tunny made to the eventual Allied victory. Bletchley Park was a medium-sized country house set in pleasant grounds; although it was a strange mixture of architectural styles, I found it came to be a likeable building. It housed some of the top army brass, including Brigadier Tiltman, the most senior army person there and himself a top cryptographer. I arrived at BP in late 1941 as a civilian and was interviewed by Tiltman. He wore his full uniform, complete with red tabs—it was an intimidating encounter.

Keywords:   British Tunny machine, Double Playfair, Hut, Russian front, chess

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