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Bletchley Park and D-Day by David Kenyon

Reviewed by Linda Parker


Yale University Press 2019

320 pages, 6 1/8 x 9 1/4 7 col. & 16 b/w illus. & 2 maps ISBN: 9780300243574 Hardcover


In this well researched and fascinating addition to the history of intelligence gathering at Bletchley Park, David Kenyon has added a new dimension to our understanding of the way in which the gathering and interpretation of signals intelligence (SIGNIT) added to the knowledge of enemy operations and strength, and how this information was analysed and used in the build up to Operation Overlord on D-Day.

David Kenyon is the Research Historian at Bletchley Park and has used recently declassified documents now placed in the National Archives, the archives of Bletchley Park and previous scholarship, for example Ralph Bennet’s Ultra in the West: The Normandy Campaign 1944-45 (Hutchinson, 1979), to analyse the growth and development of intelligence gathering at Bletchley. The gathering of information which was to be so crucial to the Allies in 1944 had been developing since 1942. Although the author’s main focus is on the contribution of the intelligence to the planning and execution of D-Day, he spends time explaining the significance of discrete developments and achievements. He stresses the importance of the breaking of the Lorenz Code and the FISH Codes, which by 1944 had given the Allies significant superiority in intelligence in that they were aware of enemy movements and initiatives in a way that did not apply to the opposing forces. At the time of D-Day, the intelligence had become so useful that Kenyon claims that “The relationship, especially between MI14 and CIS went from one of being a ‘delivery service’ and ‘customer’ to being one of an intelligence partnership and collaboration.” (p.148).


Kenyon then moves on to the role of SIGINT in the invasion and its aftermath as allied troops maintained a beachhead and moved into Europe. He poses two central questions: “What part did Bletchley Park play in the planning and execution of Overlord and the subsequent campaign in Normandy, and how useful to that campaign was the strategic SIGINT produced at Bletchley?” (p. 236). In the following chapters he then sets out to prove the central role of Bletchley in both regards.


On the 5th and 6th June 1944 Bletchley Park was monitoring the unfolding situation by decrypts of German Naval traffic. Turnaround of messages was swift, on average two and a half hours. The author contends that the Admiralty was receiving messages “In a time frame that allowed them to be operationally significant”. (p.185). Also the defensive measures of the German U-boats were being closely monitored due to the progress made in breaking SHARK in 1943. During the night of 5/6th June messages were travelling from Bletchley to the OC at the Admiralty and also directly to Admiral Ramsey and his Allied Naval Commander in Chief Expeditionary Force (ANCXF). Two detailed examples of SIGNIT being used in the immediate planning and change of planning at D-Day are recounted in detail. One concerning the US airdrop on the Cotentin Peninsula, in which such intelligence was clearly of use, and one concerning the supposed failure to detect the German 352 Infanterie-Division at Omaha Beach.


Once the allied troops were ashore the signals intelligence continued to be of value. The author again gives interesting details of how the intelligence was used, an example being the monitoring of the progress of the German units in other parts of France towards Normandy. The progress of the eleven day journey of the 2 SS-Panzerdivision from Southern France to Normandy was closely followed through SIGNIT. Kenyon asserts that it was “This strategic-level intelligence that ULTRA did so well.”(p.224).


Kenyon concludes that by 1944 Bletchley Park had reached a state of almost industrialised sophistication, which was able to act as a multi-source intelligence agency able to put collected SIGINT into context for the benefit of the allied commanders. He claims that it was no longer a place which merely turned “Enigma into Ultra” and that it played a major role in the preparation and enactment of D-Day. An interesting point that is clearly made is that the D-Day invasion might not have been attempted without the ability to gauge the strength of the enemy and to predict its movements.


In a section towards the end of the book the author explains the use he has made of his sources and gives recommendations for further reading, paying tribute to the work of Ralph Bennet who worked at Bletchley Park from 1941-1945, but considers that Bennet’s analysis was not complete as he did not have access to documents which are now declassified. Harry Hinsley’s work is also cited as a “jumping off point”, but his work is characterised by Kenyon as placing much emphasis on the final intelligence product from Bletchley rather than the processes by which this intelligence was produced.


Kenyon has used the documents released in the 1990s and in the early 2000s, such as the papers of the Western Front Committee in 2004, to produce an argument which he claims incorporates both strands of analysis, incorporating the activities of the men and women who broke the codes and the overall influence of the intelligence on events in the Second World War.


The bibliography and Kenyon’s notes on further reading show how many volumes have been produced in the last 30 years alone. Some have been general and social histories of the Park, for example Michael Smith’s The Secrets of Station X, How the Bletchley Park Code Breakers Won the War (Biteback, 2011) and some have been more specifically on the breaking of various codes, for example Hugh Sebag-Montefiore’s Enigma, The Battle for the Code (Wiley, 2000). Kenyon has used these sources and his own extensive research to paint a rounded picture of the activities at Bletchley in all aspects of the work carried out there.


In Bletchley Park and D-Day, Kenyon has made a significant contribution to the historiography of the work of Bletchley in focusing of the development of SIGNIT intelligence to the stage where it became crucial to the planning and execution of Operation Overlord and the Battle for Normandy.

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© 2019 by the Second World War Research Group.

Background Image: Units of the 21st Australian Infantry Brigade marching along a winding track in the foothills of the Finisterre Ranges on their way to the Ramu Valley after being relieved, November 1943. Photograph by Norman Stuckley. (Source: Australian War Memorial)

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