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Bletchley Park and D-Day: The Untold Story of How the Battle for Normandy Was Won
Since the secret of Bletchley Park was revealed in the 1970s, the work of its codebreakers has become one of the most famous stories of the Second World War. But cracking the Nazis’ codes was only the start of the process. Thousands of secret intelligence workers were then involved in making crucial information available to the Allied leaders and commanders who desperately needed it.
Using previously classified documents, David Kenyon casts the work of Bletchley Park in a new light, as not just a codebreaking establishment, but as a fully developed intelligence agency. He shows how preparations for the war’s turning point—the Normandy Landings in 1944—had started at Bletchley years earlier, in 1942, with the careful collation of information extracted from enemy signals traffic. This account reveals the true character of Bletchley's vital contribution to success in Normandy, and ultimately, Allied victory.
Using previously classified documents, David Kenyon casts the work of Bletchley Park in a new light, as not just a codebreaking establishment, but as a fully developed intelligence agency. He shows how preparations for the war’s turning point—the Normandy Landings in 1944—had started at Bletchley years earlier, in 1942, with the careful collation of information extracted from enemy signals traffic. This account reveals the true character of Bletchley's vital contribution to success in Normandy, and ultimately, Allied victory.
320 pages, Hardcover
First published July 16, 2019
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275 people want to read
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Displaying 1 - 22 of 22 reviews
September 24, 2019
This book shows the clearest use of intelligence intercepts from their initial receipt to their final use. The best narrative for fully understanding the role of Bletchley Park (and by extension the "Y" Stations and Arlington Hall) in the Second World War
March 3, 2021
The WWII codebreaking work at Bletchley Park is always a fascinating topic. Mostly, books about it tend to focus on its most famous exploit, the breaking of the Enigma code. Kenyon goes beyond that, taking an in-depth look at the many different facets of the achievements at Bletchley and how these efforts were vital for the success of the D-Day landings. Informative and very interesting reading.
May 18, 2021
Great book full of wonderful stuff... but so dry... bring a few bottles of water before you start this one.🙄
February 9, 2022
Great thorough look at the intelligence work completed through the Bletchley team. Covers from the commencement and progression of their success.
December 23, 2024
Extremely well researched and enhanced my knowledge of the work done at Bletchley Park. That said, the author gets frequently bogged down in details which hurts his overall storytelling, something Ben Macintyre has nailed in this genre.
September 15, 2019
“Bletchley Park and D-Day: the untold story of how the battle for Normandy was won,” by David Kenyon (Yale, 2019). Add a star if are really fascinated with the inner workings of the code-breaking operations. Kenyon is the research historian at Bletchley Park. Here are the fruits of an exhaustive examination into records by and about the legendary British cryptanalytic station. This goes far beyond movies such as “the Imitation Game” about the tormented genius Alan Turing, and many other brilliant men (and some women) who learned how to decipher German codes---not just Enigma, but other German cipher machines. It is fairly dry, although Kenyon tries to provide as much human color as he can in a story that is mostly about the mechanical and organizational operations that ultimately laid bare almost all the German order of battle, defensive plans, and operations leading up to and during the D-Day invasion. He describes not just the machines, but the buildings they were housed in, how people were recruited, what morale was like. It is remarkable that the people doing the daily work did not know quite what they were doing: they didn’t know what the messages were nor how they were used. It wasn’t just one man or one machine finally breaking a code. The codes were constantly being changed, the machines that made them were being modified almost daily, and the analysts had to break them constantly to keep the information flowing. Kenyon describes the mechanical operation of the machines, the organizations in Bletchley Park and far-flung receiving stations that got the German signals and passed them along. Thousands of men and women were involved, and they got details about the Germans down to the quality of the tanks that would be facing the Allies. Finally, Kenyon says, the greatest value of the code-breakers was in long-term, strategic information: they couldn’t get the information out fast enough to be truly useful in the fluid tactical situations as the battle developed. Essentially, the Allies knew exactly who and what they were facing; they knew what Hitler and his generals were thinking; they knew the divisions facing the landing beaches, and how long it took for reinforcements to arrive under constant air attack. For me, it was a bit of a slog to get through. But it is good to know how complex and challenging the code-breaking was, and how many people were involved in bringing the Allies the information they needed. The code-breakers certainly did shorten the war, even if it is not always possible to point at specific battles and say “Ultra did this.” Kenyon settles old debates and feuds about who did what and what mistakes were made.
https://yalebooks.yale.edu/book/97803...
https://yalebooks.yale.edu/book/97803...
May 16, 2022
This book is a detailed and factual analysis that provides engaging insights on the role of Bletchley Park and it role in the Battle for Normandy
Early chapters focus upon the procedures and processes developed by British intelligence and code breakers.
The author goes to considerable length to put such detail in a procedural context, making it dense reading yet offering excellent analysis.
The conclusion reached is that the allies gained considerably from from the early efforts in codebreaking analysis and subsequently developed a range of strategies that were successfully used. Readers who are seeking information about the breaking of Enigma machine may be a little disappointed because this text focuses very broadly indeed.
The final chapters present the D-Day landings and subsequent military engagements in the context of intelligence material provided from Bletchley Park. This was the most interesting part of the book. The detail presented had a direct correlation with the military decisions being made by both the Allies and Nazi Germany.
I found the discussion extremely interesting but I could not claim to fully understand all the material presented.
The text is highly informative with a narrative that was fascinating without being a triumphal war story.
This is good war history that is very well written if somewhat difficult to read.
Early chapters focus upon the procedures and processes developed by British intelligence and code breakers.
The author goes to considerable length to put such detail in a procedural context, making it dense reading yet offering excellent analysis.
The conclusion reached is that the allies gained considerably from from the early efforts in codebreaking analysis and subsequently developed a range of strategies that were successfully used. Readers who are seeking information about the breaking of Enigma machine may be a little disappointed because this text focuses very broadly indeed.
The final chapters present the D-Day landings and subsequent military engagements in the context of intelligence material provided from Bletchley Park. This was the most interesting part of the book. The detail presented had a direct correlation with the military decisions being made by both the Allies and Nazi Germany.
I found the discussion extremely interesting but I could not claim to fully understand all the material presented.
The text is highly informative with a narrative that was fascinating without being a triumphal war story.
This is good war history that is very well written if somewhat difficult to read.
January 11, 2022
This is primarily the story of Allied (mostly British) code (cipher) breaking during WWII, and secondarily what impacts it had on the overall war effort and D-Day in particular. It’s focused on German code breaking but includes info about breaking Japanese and other codes as well. What I came away with was profound respect for not just the talented analysts (code breakers), linguists, intelligence experts, and all others who played a part in this multi-year effort, but also for leadership who had a vision for what was possible and provided the resources. The task was Herculean given the multiplicity of codes/ciphers used by various branches of the German military, let alone individual units, and the constantly changing codes/ciphers. This was not a matter of breaking a single code, but involved solving the riddle to constantly changing codes. Amazing story!
February 8, 2023
Romanticized accounts of the World War II codebreakers at Bletchley Park convey the impression of a cozy community of brainy people with Oxford and Cambridge degrees laboring in isolation in the countryside. And there is some truth in this picture during the first two years of the war. But that changed. By mid-1944, as the Normandy Invasion approached, 7,500 men and women—some three-quarters of them women, as it happened—worked there. They slogged away, day after day, in a cold, sprawling campus fifty miles from London. The place is studded with makeshift huts and drab concrete and steel buildings on 58 acres. By 1945, the head count there grew to almost 9,000 working in three shifts around the clock. The crowding and primitive working conditions resembled a factory more than a military installation, much less an academic campus. Kenyon views it as the Bletchley Park intelligence factory.
A LARGER ROLE IN WINNING THE WAR THAN JUST CODE-BREAKING
Thus, Bletchley Park was far from cozy. And in no way was the staff there isolated from the war effort. Because Bletchley Park played a larger role in the unfolding conflict than simply breaking the famous Enigma, Lorenz, and Japanese Purple ciphers and codes. British historian David Kenyon ably tells the story in Bletchley Park and D-Day.
“AN INTELLIGENCE AGENCY IN ITS OWN RIGHT”
Robert Hannigan is the former director of GCHQ, Britain’s counterpart to the US National Security Agency and the successor to Bletchley Park. In a foreword to the book, he writes: “Seldom have commanders known more about their opponents in advance of a battle than the Allies did on 6 June 1944. Much of that knowledge was acquired at Bletchley Park.” Note the emphasis on knowledge, as distinguished from raw data. That was the true product of the Bletchley Park intelligence factory.
Kenyon explains that the staff at Bletchley Park were “carrying on a wide variety of intelligence analysis functions and producing an equally wide range of product, from urgent teleprints to multi-page long-term assessment reports. This is perhaps one of the least well understood parts of Bletchley, but was undoubtedly one of the most important, lifting GC&CS from the position of merely a decryption and translation service to the status of what would be considered in more modern terms an ‘intelligence agency’ in its own right.” Of course, in many popular accounts, we may see military couriers rushing into Winston Churchill’s office bearing messages from Bletchley marked “ULTRA.” And that happened from time to time. But it’s only a small part of the true picture.
PIECING TOGETHER THE GERMAN ORDER OF BATTLE
Much of Kenyon’s book revolves around the often frantic effort at Bletchley Park in the run-up to the invasion to determine the German “order of battle” in Normandy. This was the critical work to identify who would face Allied troops when they stormed the beaches. The enemy units. Their troop strength. The arms and equipment they possessed. Their commanders. And precisely where they were located. And Bletchley succeeded brilliantly at this task.
There were errors, as Kenyon concedes, but few of them. And Kenyon makes the case that this knowledge, fed to Allied commanders on the ground, was a major factor in the success on D-Day and the succeeding weeks in the Battle of Normandy. Popular accounts of that campaign often credit Operation Fortitude and Operation Double Cross—the most famous parts of the overall Anglo-American deception campaign called Operation Bodyguard—with a major share of the credit. But knowing the German order of battle was at least as important.
It is difficult to overstate the importance of that intelligence about the German strength on the ground. At the Tehran Conference late in 1943, “the president and prime minister had agreed to the invasion on the basis of quite restrictive estimates of the strength of likely opposition. In short, if Allied intelligence detected radical changes made by the Germans that had not been predicted by the planners, the invasion would be either cancelled or postponed.” As it was, German strength in Normandy came close to those limits but never crossed the line.
OVERALL ASSESSMENT OF THE BOOK
Bletchley Park and D-Day is not meant for casual reading. In fact, it reads more like a text intended for military historians and military officers. The density of detail is staggering, and I found myself skimming through much of the text (which I rarely do). But the book is worth it for anyone with an interest in understanding exactly what happened on D-Day and in the Battle of Normandy that followed—and why. David Kenyon significantly adds to that understanding with this microscopic view of the role signals and communications intelligence played there.
ABOUT THE AUTHOR
British archaeologist and military historian David Kenyon is the Research Historian at Bletchley Park. According to Wikipedia, “He is known for his work on presenting and interpreting World War I history at public events and in the media.” Kenyon is the author or coauthor of three books of military history, the most recent of which is Bletchley Park and D-Day.
A LARGER ROLE IN WINNING THE WAR THAN JUST CODE-BREAKING
Thus, Bletchley Park was far from cozy. And in no way was the staff there isolated from the war effort. Because Bletchley Park played a larger role in the unfolding conflict than simply breaking the famous Enigma, Lorenz, and Japanese Purple ciphers and codes. British historian David Kenyon ably tells the story in Bletchley Park and D-Day.
“AN INTELLIGENCE AGENCY IN ITS OWN RIGHT”
Robert Hannigan is the former director of GCHQ, Britain’s counterpart to the US National Security Agency and the successor to Bletchley Park. In a foreword to the book, he writes: “Seldom have commanders known more about their opponents in advance of a battle than the Allies did on 6 June 1944. Much of that knowledge was acquired at Bletchley Park.” Note the emphasis on knowledge, as distinguished from raw data. That was the true product of the Bletchley Park intelligence factory.
Kenyon explains that the staff at Bletchley Park were “carrying on a wide variety of intelligence analysis functions and producing an equally wide range of product, from urgent teleprints to multi-page long-term assessment reports. This is perhaps one of the least well understood parts of Bletchley, but was undoubtedly one of the most important, lifting GC&CS from the position of merely a decryption and translation service to the status of what would be considered in more modern terms an ‘intelligence agency’ in its own right.” Of course, in many popular accounts, we may see military couriers rushing into Winston Churchill’s office bearing messages from Bletchley marked “ULTRA.” And that happened from time to time. But it’s only a small part of the true picture.
PIECING TOGETHER THE GERMAN ORDER OF BATTLE
Much of Kenyon’s book revolves around the often frantic effort at Bletchley Park in the run-up to the invasion to determine the German “order of battle” in Normandy. This was the critical work to identify who would face Allied troops when they stormed the beaches. The enemy units. Their troop strength. The arms and equipment they possessed. Their commanders. And precisely where they were located. And Bletchley succeeded brilliantly at this task.
There were errors, as Kenyon concedes, but few of them. And Kenyon makes the case that this knowledge, fed to Allied commanders on the ground, was a major factor in the success on D-Day and the succeeding weeks in the Battle of Normandy. Popular accounts of that campaign often credit Operation Fortitude and Operation Double Cross—the most famous parts of the overall Anglo-American deception campaign called Operation Bodyguard—with a major share of the credit. But knowing the German order of battle was at least as important.
It is difficult to overstate the importance of that intelligence about the German strength on the ground. At the Tehran Conference late in 1943, “the president and prime minister had agreed to the invasion on the basis of quite restrictive estimates of the strength of likely opposition. In short, if Allied intelligence detected radical changes made by the Germans that had not been predicted by the planners, the invasion would be either cancelled or postponed.” As it was, German strength in Normandy came close to those limits but never crossed the line.
OVERALL ASSESSMENT OF THE BOOK
Bletchley Park and D-Day is not meant for casual reading. In fact, it reads more like a text intended for military historians and military officers. The density of detail is staggering, and I found myself skimming through much of the text (which I rarely do). But the book is worth it for anyone with an interest in understanding exactly what happened on D-Day and in the Battle of Normandy that followed—and why. David Kenyon significantly adds to that understanding with this microscopic view of the role signals and communications intelligence played there.
ABOUT THE AUTHOR
British archaeologist and military historian David Kenyon is the Research Historian at Bletchley Park. According to Wikipedia, “He is known for his work on presenting and interpreting World War I history at public events and in the media.” Kenyon is the author or coauthor of three books of military history, the most recent of which is Bletchley Park and D-Day.
April 26, 2021
This book gives a lot of good additional information behind the intelligence around the Normandy landings in 1944 during WWII. Told by a Brit, it gives good insight into the happenings of the events around the planning of the invasion, where the forces were and counter-intellegence. It gives a good represenation of how intelligence and counter-itellegence held the sway of battle. It also shows how important SIGINT was to play in calculating the strategy of the battles. Very good supplement to understanding the battle and how it unfolded. Most of the books I've read in the past give an overview of the operation, the forces involved and how the battle unfolded with first-hand stories of those that lived past the battle. This gives an insight into the information that was at the hands of those that planned the invasion and how they came to make the decisions that were made.
March 6, 2023
A quickreading accounting of how Bletchley Park using Enigma and Ultra helped to prepare the Allied assault on June 6, 1944. I don't pretend to understand all the terms used, but it is enough to say that brilliant minds and hard work helped to bring about victory.
Not to take anything from the work and intelligence of the Allies on the Western Front, but I have often wondered if D-Day would even have been possible had the Germans not lost so many men on the Eastern Front? Hitler's mistakes on both fronts opened the door to success by the Allies.
Not to take anything from the work and intelligence of the Allies on the Western Front, but I have often wondered if D-Day would even have been possible had the Germans not lost so many men on the Eastern Front? Hitler's mistakes on both fronts opened the door to success by the Allies.
February 5, 2025
Bletchley Park and D-Day is an incredibly well researched book, going into such detail that in a strange way it detracts from the story itself. The books covers the period of WWII from around 1942 up to and beyond the D-Day invasion in June 1944. The prose does tend to be a bit dry as a result of all the details included, the data on the number of intercepts the days of turnaround etc. However, it does show the tremendous work done but the people involved with GC&CS, Bletchley Park on the outlying stations to provide data for the planning and execution of the D-Day invasion.
April 5, 2023
A intriguing account of what Bletchley Park produced after the initial enigma code was broken. The amount of day to day hard work performed miracles in analyzing emery movements and plans. Also an interesting account of cooperative espionage across agencies and countries. if you are interested in the details of WWII this is a book you should read.
January 13, 2020
A very interesting book which challenges a few of the Bletchley Park stories. It highlights how BP became an intelligence provider on an industrial scale and the importance of people with work process skills in this process.
April 29, 2024
Fact-packed and especially valuable when describing the Bletchley Park setup in 1944. Could have chosen to focus more on one part or the other i.e. Bletchley Park structure and operations 1944 or the impact od decryption on Overlord operations
November 22, 2021
Very good! Meticulously documented.
February 15, 2023
Very interesting. Brought to life the extended impact the Bletchley Park had on the war planning. Far beyond the Battle of the Atlantic.
March 1, 2023
This was very technical and thin on story. I’m sure if a reader is very tech savvy, it was more interesting.
July 14, 2024
3.5 stars
Interesting yet dry! More logistical than dramatic as I would have hoped but alas I guess intelligence really is that battalion X has moved 4 miles. I just wanted spicier intelligence.
Interesting yet dry! More logistical than dramatic as I would have hoped but alas I guess intelligence really is that battalion X has moved 4 miles. I just wanted spicier intelligence.
August 29, 2024
Exhaustive research. This book is very interesting, but told from the British view. I'm wondering just why Americans bothered to respond to aid the Normandy war effort.
July 20, 2025
Unsatisfying
The author himself acknowledges that only the last part of the book deals with D-Day, and he's right. Too much background and not enough truly interesting material.
The author himself acknowledges that only the last part of the book deals with D-Day, and he's right. Too much background and not enough truly interesting material.
August 22, 2025
An excellent account a much uninformed part of the Bletchly complex
Displaying 1 - 22 of 22 reviews