Bletchley Park and D-Day: The Untold Story of How the Battle of Normandy Was Won

By David Kenyon

“Demonstrates that the intelligence division . . . had a more significant role in WWII . . . making indispensable contributions to the invasion at Normandy.” (Publishers Weekly)

The untold story of Bletchley Park's key role in the success of the Normandy campaign

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.
 

• Language: English
• Publisher: Yale University Press
• Release date: Jul 16, 2019
• ISBN: 9780300244809

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BLETCHLEY PARK AND D-DAY

Copyright © 2019 David Kenyon

All rights reserved. This book may not be reproduced in whole or in part, in any form (beyond that copying permitted by Sections 107 and 108 of the U.S. Copyright Law and except by reviewers for the public press) without written permission from the publishers.

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Set in Minion Pro Regular by IDSUK (DataConnection) Ltd

Printed in Great Britain by TJ International Ltd, Padstow, Cornwall

Library of Congress Control Number: 2019938490

ISBN 978-0-300-24357-4

A catalogue record for this book is available from the British Library.

10  9  8  7  6  5  4  3  2  1

The king hath note of all that they intend,

By interception which they dream not of.

Shakespeare, Henry V, Act II, Scene 2

CONTENTS

Foreword by Robert Hannigan

List of illustrations and maps

List of abbreviations, codenames and technical terms

A note on military units and ranks

Introduction: Overture to OVERLORD

PART I BLETCHLEY PARK IN 1944

1 The intelligence factory

2 Incoming intercepts and codebreaking

3 Outgoing intelligence

PART II PREPARATIONS FOR INVASION

4 Invasion planning in 1943: the Western Front Committee

5 Invasion planning in 1944: SHAEF and JELLYFISH

6 Understanding German expectations

PART III INVASION AND AFTER

7 Getting ashore: Operation NEPTUNE and the landings

8 Staying ashore: the Normandy Campaign

9 The importance of Bletchley Park to OVERLORD

A note on sources and further reading

Endnotes

Acknowledgements

Index

FOREWORD

ROBERT HANNIGAN

Former Director of the Government Communications Headquarters (GCHQ) Cheltenham and Trustee of Bletchley Park

The enduring memory of D-Day is one of extraordinary human courage, ambition and sacrifice. The scale of the invasion on 6 June 1944, when more than 130,000 US, British, Canadian and other Allied troops crossed the English Channel, preceded by 23,000 airborne soldiers, is staggering; it remains the largest amphibious assault in history. The names of the Normandy beaches – Omaha, Utah, Juno, Gold, Sword – onto which young soldiers threw themselves under heavy fire have passed into the language as examples of extreme bravery. The events of Operation OVERLORD and its subsidiary plans have rightly been chronicled in some fine histories and immortalised in films over the past seventy-five years.

But the ultimate success of the invasion force, and the 2 million Allied personnel who fought their way across Europe in the following months, tends to obscure just how risky the operation was and how precarious its early days and weeks. So uncertain were the first twenty-four hours that General Eisenhower, as Supreme Allied Commander, famously drafted a statement accepting full personal responsibility for its failure, which had been based on ‘the best information available’. The key part of that information, alongside everything from weather forecasting to estimates of the topography of the landing beaches, was intelligence. Examining the role of that intelligence and its importance to the Allied victory has been the subject of a number of studies, often focusing on the gripping stories of deception operations by secret agents to convince German commanders that the attack would take place elsewhere, or dummy landing craft designed to fool German reconnaissance flights. But until now there has been no single account which tells the story of the central role played by Bletchley Park and evaluates its importance.

Since the veil was lifted in the early 1970s on the codebreaking work of the Government Code and Cipher School (GC&CS) at Bletchley Park, historians have tended to focus on three areas. There are detailed technical accounts of mathematical and cryptanalytic achievements and how machines like Enigma were broken; biographies of extraordinary and sometimes eccentric individuals whose contributions were seminal, notably Alan Turing; and popular accounts of the unusual daily life of staff at Bletchley Park. What has sometimes been missing, particularly in relation to D-Day, is an evaluation of what the intelligence that was produced actually achieved and whether it made a significant difference. Codebreaking was not an end in itself, intellectually challenging as it was, and unless it could be used by the right people in a timely way it was of little value.

Addressing these questions, David Kenyon’s book breaks new ground in a number of areas. In addition to a highly readable account of how Bletchley Park came to be, and an admirably comprehensible description of the codebreaking process, he focuses in a new way on the intelligence production factory which Bletchley Park had become by 1944. It was no longer a small-scale and eclectic operation, but, from the large network of Y stations intercepting traffic, passing it through Bletchley and its subsidiaries to commanders in the field, it had become a slick and agile industrial producer of intelligence. Just as importantly, Bletchley was by now assimilating intelligence from sources way beyond intercepted messages, a point brought out in depth here for the first time.

This account therefore shows GC&CS at the very height of its powers and reach. It was grappling with all the problems which those of us who worked in its successor organisation, GCHQ, will recognise: constantly keeping up with new technology or cryptological advances by the enemy; disseminating intelligence to the right commanders in a timely way that made it predictive, rather than purely academic; and prioritising from a vast volume of traffic to find intelligence that would be game-changing.

As this book reminds us, Bletchley Park could only decrypt a very small percentage of the messages intercepted. Choosing which traffic to select was therefore critical. Much of the focus in popular accounts of the codebreakers has been on Enigma – and this was certainly of vital importance throughout, especially in winning the Battle of the Atlantic, without which an invasion across the English Channel would have been unthinkable. However, this study rightly emphasises the importance of other achievements: the cracking of the Lorenz machine which allowed access to the messages of the German High Command, and the American breaking of Japanese diplomatic ciphers, shared with Bletchley, which enabled the Allies to read detailed Japanese accounts of German plans in Europe.

The result, as this book shows, was that GC&CS was producing an unparalleled insight into German thinking, strategy and detailed orders of battle. This was of enormous practical importance for Allied commanders: they had never been better informed about the enemy’s strength or its plans. This picture was not complete or perfect – intelligence rarely is – but it gave assurance to commanders about the threats they were facing and the risks they were taking. From Hitler’s and Rommel’s personal thinking, to battle orders of local commanders and whether the clever Allied deception operations were working, there was little that GC&CS could not shed some light upon.

Pace was a constant challenge for GC&CS, particularly as the Normandy invasion itself got underway. David Kenyon describes the gripping drama of the first day and his account is infused with stories of individuals which bring the history to life. For students of intelligence, his insights into the human management challenges of the SIGINT factory that GC&CS had become are particularly valuable.

As the official research historian at Bletchley Park, Kenyon could be forgiven for eulogising its achievements. But he never overstates its value and subjects some previous claims to scrutiny. He examines perceived failures, for example the suggestion that Allied intelligence missed the scale of German forces defending Omaha beach. His conclusions about the importance of ULTRA material in very significantly reducing the risks of the invasion for the Allies are all the more powerful as a result.

The final D-Day tribute should always go to those who died, some 10,000 Allied soldiers on the first day alone. Key staff at Bletchley appreciated, as the days unfolded, the scale of suffering of those fighting in France, in contrast to their own work in the safety of Bletchley, however exhausting it might be. That those Allied casualties were significantly lower than the figures estimated by Eisenhower’s planners, and that their sacrifice led to victory, is where Bletchley Park can rightly claim to have played a major role. David Kenyon has done us a great service in uncovering and describing how this happened.

ILLUSTRATIONS AND MAPS

ILLUSTRATIONS

IN PLATE SECTION

1. Gerd von Rundstedt meets Erwin Rommel in Paris, December 1943. Bundesarchiv, Bild 101I-718-0149-18A / Photographer: Jesse.

2. General Ōshima touring the Atlantic Wall with other Japanese and German officials, September 1943. Bundesarchiv, Bild 101I-262-1544-13 / Photographer: Werner.

3. Eric Jones, head of Hut 3, 1957. © National Portrait Gallery, London.

4. Brigadier John Tiltman, head of Military Section at Bletchley Park. Courtesy of the George C. Marshall Foundation, Lexington, Virginia.

5. William ‘Bill’ Tutte, member of Bletchley Park Research Section. Courtesy of Richard Youlden.

6. A ‘Morrison Wall’ at Bletchley Park. Crown Copyright. Reproduced by kind permission, Director GCHQ.

7. A Robinson machine in the Newmanry at Bletchley Park. Crown Copyright. Reproduced by kind permission, Director GCHQ.

8. Bombe machines in ‘Greece’ bay at Eastcote Outstation. Crown Copyright. Reproduced by kind permission, Director GCHQ.

9. Block D at Bletchley Park. Photo: Andy Stagg.

10. An Enigma I cipher machine as used by the German army and air force. Photo: Will Amlot.

11. A Lorenz SZ42 cipher machine with its protective cover removed. © Shaun Armstrong / mubsta.com.

12. A US-built analogue of the Japanese PURPLE diplomatic cipher machine. Granger Historical Picture Archive / Alamy Stock Photo.

13. The teleprinter copy of an intercepted German Enigma message. Crown Copyright. Reproduced by kind permission, Director GCHQ.

14. The deciphered German plaintext of the message in Plate 13. Crown Copyright. Reproduced by kind permission, Director GCHQ.

15. The deciphered version of an intercepted FISH message, February 1945. Crown Copyright. Reproduced by kind permission, Director GCHQ.

16. The handwritten transcript of a German naval Enigma message transmitted on 6 June 1944. Crown Copyright. Reproduced by kind permission, Director GCHQ.

17. A list of ‘Sources and Contributors’ from the ‘Record of the Western Front’ (No. 27; 10 March 1944). Crown Copyright. Reproduced by kind permission, Director GCHQ.

18. Generalfeldmarschall Rommel inspects the Atlantic Wall defences, April 1944. Bundesarchiv, Bild 101I-719-0243-33 / Photographer: Jesse.

19. Rommel inspects a self-propelled artillery unit of 21. Panzer-Division, Normandy, May 1944. Bundesarchiv, Bild 101I-300-1865-06 / Photographer: Speck.

20. A German propaganda photo of a paratrooper from Fallschirmjäger-Regiment 6, Cotentin peninsula, June 1944. Bundesarchiv, Bild 101I-587-2253-17 / Photographer: Toni Schneiders.

21. Canadian infantrymen in a Landing Craft Assault (LCA) going ashore from HMCS Prince Henry off the Normandy beachhead, 6 June 1944. Library and Archives Canada / Department of National Defence fonds / a132790.

22. Troops of the 9th Canadian Infantry Brigade (Stormont, Dundas and Glengarry Highlanders) going ashore from LCI (L) 299 [Landing Craft Infantry], Bernières-sur-Mer, Normandy, 6 June 1944. Library and Archives Canada / Department of National Defence fonds / a122765.

23. US troops of Company A, 16th Infantry, 1st Infantry Division (the ‘Big Red One’) wading onto Omaha Beach on the morning of 6 June 1944. Courtesy of the Franklin D. Roosevelt Library, Hyde Park, New York.

IN TEXT

Part I. Interior of Hut 6. Crown Copyright. Reproduced by kind permission, Director GCHQ.

Part II. A soldier in the gun bunker looking over the beach, Etretat, 1944. Bundesarchiv, Bild 101I-299-1809-14 / Photo: Scheck.

Part III. British commandos of 1st Special Service Brigade, led by Lord Lovat, landing on ‘Queen Red’ sector of Sword Beach, at La Breche, on the morning of 6 June 1944. Imperial War Museum / J.L. Evans. B 5103.

MAPS

1. German army dispositions, dawn, 6 June 1944.

2. Normandy, showing German defensive positions, 6 June 1944.

ABBREVIATIONS, CODENAMES AND TECHNICAL TERMS

A NOTE ON MILITARY UNITS AND RANKS

Wherever possible in this account, German military units and formations have been given in their original form, rather than being translated (except when they occur in direct quotations of wartime documents).

For clarity, and in keeping with UK military historical practice, Axis formations are rendered in italics thus: Heeresgruppe B, 6. Armee, XLVII. Panzer-Korps, 3. SS-Panzer-Division, Grenadier-Regiment 920.

Where unit types are not readily understandable, translations are provided (e.g. Fallschirmjäger – ‘paratrooper’).

GERMAN ARMED FORCES RANKS AND THEIR APPROXIMATE EQUIVALENTS IN ENGLISH

INTRODUCTION

OVERTURE TO OVERLORD

Arromanches, 1 June 1944. General der Artillerie Erich Marcks stood on the high bluff above the Normandy beach resort studying the grey English Channel. As commander of the German LXXXIV. Armeekorps , he had responsibility for defending this section of coast. A slim man, with a sharp nose and chin, his round, gold-rimmed glasses lent him the appearance more of a history professor than a soldier. And yet Marcks knew a great deal about soldiering. Having joined the old Imperial Army in 1910, he had served throughout both the Great War and the present conflict. Though suspected of being lukewarm towards National Socialism, his military prowess had brought him high rank, and he sported the ribbons of an Iron Cross First Class (awarded in 1915) and a more recent Knight’s Cross.

After the French campaign of 1940, he had moved east – first to help plan the invasion of the Soviet Union, and then to command a division on the Eastern Front. Two of his three sons had been killed in Russia, and he himself had lost a leg in 1942 in Ukraine.

Now he was back in Normandy. His mind was not on the leaden waves, but on what lay beyond, across the Channel. According to German intelligence, the Allies had nearly 80 divisions in England preparing for the invasion. At a rough guess, that was over a million men. It was also estimated that there were enough landing craft to transport a quarter of those soldiers in a single operation – twenty divisions in one fell swoop.

What did he have? Just three divisions to defend the 50 miles (80km) of coast for which he was responsible. And not for him the young, milk-fed farm boys of the US Army, their pockets full of chewing gum and chocolate . . . Half of his force comprised ‘static’ units – men of thirty or forty years of age, many (like himself) saddled with wounds from Russia or suffering from medical conditions. And then there were the teenagers, who knew a lot about National Socialism but precious little about fighting. Some weren’t even German! Two of his battalions consisted of former PoWs, Poles or anti-communist Ukrainians and others recruited from the occupied territories in the east. Their weapons were old, including antiquated captured French equipment; in his only panzer division, many of the tanks were French and dated back to 1940, or else artillery pieces hastily mounted on outdated chassis.

To cap it all, the defences were incomplete. Despite the huge investment of concrete and steel in the Führer’s ‘Atlantic Wall’, most of it had gone on the more strategically obvious invasion beaches of the Pas-de-Calais. The beaches of Normandy had only belatedly received serious attention when Rommel arrived in late 1943. Many of Marcks’ men were still shielded only by earthen trenches and sandbags – and he himself had bitter experience from 1915 of what it was like to withstand a bombardment with only soil for protection.

But, supposedly, there was little to worry about. Von Rundstedt, the commander in the west, had first declared the invasion imminent at the end of March. But April and May had passed without incident. Readiness had waned – how could you be in a constant state of alertness for weeks on end? And, anyway, all the predictions were that the weather in early June would be atrocious.

So unlikely did the Top Brass consider an imminent Allied invasion to be that Marcks and all his senior commanders were due to go to Rennes on 5 June for a staff training wargame. For the exercise Marcks had been picked to command the Allied landing forces – could it be an ironic dig at his suspected lack of enthusiasm for Nazism? In any case, Hitler had confidently predicted only days before that if an invasion did occur in Normandy, it would only be a feint, before the main event at Calais.

But Marcks was not so sure. As he surveyed the Channel, he turned to his aide, an army captain:

If I know the British, they will go to church next Sunday for one last time, and sail on Monday. Army Group B says they’re not going to come yet, and when they do come it’ll be at Calais. So I think we’ll be welcoming them on Monday right here.

In the event, Marcks was wrong: bad weather caused the Allied invasion – codenamed OVERLORD – to be postponed for twenty-four hours. But it came on Tuesday, 6 June, Marcks’ fifty-third birthday. He just had time to raise a glass in celebration on the evening of the 5th before heading for Rennes. By then, the first Allied parachute and glider troops were in the air over the Channel.

Within a week Marcks was dead, the 50 miles of coast for which he had been responsible were in Allied hands, and the chances of the Germans pushing the invaders back into the sea were fading fast.

In fact, the 80 Allied divisions that German intelligence and senior commanders had warned Marcks about were a fiction, cooked up by Allied intelligence to mask their actual intentions. The Germans knew next to nothing about the real invasion to come. In contrast to these fairy tales, the Allied commanders knew exactly what threat they were facing across the Channel, and they knew how to defeat it. That knowledge had started to be assembled years before – much of it at Bletchley Park.

*

All military operations, from the earliest times, have required a secret intelligence effort. It is necessary to know who and where your enemy is, and what he intends. This information should also be obtained without the knowledge of the enemy, since if he realises that his plans are compromised, he will inevitably alter them. This was as true for Shakespeare’s Henry V as it was for Wellington at Waterloo, or for Eisenhower or Montgomery on D-Day.

The Allied invasion of Europe on 6 June 1944 and the fighting in Normandy that followed undoubtedly constitute the most famous campaign of the Second World War. Almost from the moment they were undertaken, these battles have been the subject of innumerable books, films and television programmes. They have also provided the backdrop for huge amounts of fiction, both on paper and on the screen. It would be fair to say that the military operations have been covered and re-covered in so many works that it would take a lifetime to digest them all. Yet the intelligence operations that actually underpinned the campaign have been curiously overlooked – either taken for granted in accounts of the campaign, or mentioned only on the rare occasions when the flow of intelligence fell short of what was expected by battlefield commanders (or indeed post-war critics).

The range of intelligence sources available to Allied commanders during the Second World War was broad indeed. They extended from basic reconnaissance and patrols on the front lines of the battlefield, to information gained by human agents behind enemy lines, whether members of the Allied secret services or local inhabitants and members of Resistance organisations. Information could also be gained through the interrogation of prisoners of war. These various sources are often grouped under the title of ‘human intelligence’, abbreviated nowadays as HUMINT. Supplementary information could