Code Breaking in the Pacific

Peter Donovan • John Mack

Code Breaking in the Pacific

123

Peter DonovanSchool of Mathematics and StatisticsUniversity of New South WalesSydney, NSW, Australia

John MackSchool of Mathematics and StatisticsUniversity of SydneySydney, NSW, Australia

Additional material to this book can be downloaded from http://extras.springer.com

ISBN 978-3-319-08277-6 ISBN 978-3-319-08278-3 (eBook)DOI 10.1007/978-3-319-08278-3Springer Cham Heidelberg New York Dordrecht London

Library of Congress Control Number: 2014945227

© Springer International Publishing Switzerland 2014This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part ofthe material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting, reproduction on microfilms or in any other physical way, and transmission or informationstorage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodologynow known or hereafter developed. Exempted from this legal reservation are brief excerpts in connectionwith reviews or scholarly analysis or material supplied specifically for the purpose of being enteredand executed on a computer system, for exclusive use by the purchaser of the work. Duplication ofthis publication or parts thereof is permitted only under the provisions of the Copyright Law of thePublisher’s location, in its current version, and permission for use must always be obtained from Springer.Permissions for use may be obtained through RightsLink at the Copyright Clearance Center. Violationsare liable to prosecution under the respective Copyright Law.The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoes not imply, even in the absence of a specific statement, that such names are exempt from the relevantprotective laws and regulations and therefore free for general use.While the advice and information in this book are believed to be true and accurate at the date ofpublication, neither the authors nor the editors nor the publisher can accept any legal responsibility forany errors or omissions that may be made. The publisher makes no warranty, express or implied, withrespect to the material contained herein.

Printed on acid-free paper

Springer is part of Springer Science+Business Media (www.springer.com)

Margaret Donovan and Vanessa Mack havehad to put up with a great deal while theresearch into the cipher war in the PacificOcean was being carried out. And so thisbook is dedicated to them.

Preface

Will no one tell me what she sings?Perhaps the plaintive numbers flowFor old, unhappy, far-off things,And battles long ago.

W. Wordsworth, The Solitary Reaper.

President Roosevelt, in his January 1943 State of the Union address, said:

The Axis Powers knew that they must win the war in 1942—or eventually lose everything.I do not need to tell you that our enemies did not win the war in 1942.

In the Pacific area, our most important victory in 1942 was the air and naval battleoff Midway Island. That action is historically important because it secured for our usecommunications lines stretching thousands of miles in every direction. In placing thisemphasis on the Battle of Midway, I am not unmindful of other successful actions in thePacific, in the air and afloat—especially those on the Coral Sea and New Guinea and inthe Solomon Islands. But these actions were essentially defensive. They were part of thedelaying strategy that characterised this phase of the war.

The President could not reveal that Allied interception and decoding of Japanesenaval radio messages played a significant role in determining the events of thePacific War in 1942 and their outcomes. Indeed, the role of Allied SignalsIntelligence in WW2 was suppressed for many years afterwards, with the earliestauthoritative accounts appearing only in the late 1970s. Even later, publications onthe events of WW2 commonly failed to address underlying contributions from thissource. Since then Bletchley Park has become a great British icon and is (at longlast) receiving appropriate maintenance. European and Atlantic Signals Intelligencehas been investigated and explained often enough for its significance to be acceptedand appreciated. For example, it is clear that the 1942 Battle of the Atlantic andthe 1944 invasion of Normandy involved much use of what is generically calledcodebreaking and that this was applied to codes based on encryption machines,notably the Enigma and Lorenz SZ42.

vii

viii Preface

The situation with regard to Signals Intelligence in the WW2 Pacific Theatre isdifferent. There is no iconic single site associated with this activity—it involvedunits around the world and some of these are almost unknown. It is well known forits crucial contributions to the 1942 Battle of Midway and the 1943 shooting downof the aircraft carrying Admiral Yamamoto. Yet it is chastised by some writers for itsclaimed failure to warn of the 1941 raid on Pearl Harbor, and its overall contributionto the evolution of the Pacific War is much less well appreciated than is the case withits European counterpart.

The methods used in the code breaking behind the successes of Allied PacificSignals Intelligence are quite different to those used against encryption machineciphers such as the Enigma. The reason is that the main cipher systems used by boththe Imperial Japanese Army (IJA) and the Imperial Japanese Navy (IJN) were basedon code books rather than a machine. This book is the first to provide a completedescription of those ‘additive cipher systems’ and the development of the techniquesused to break various implementations of them. In doing so, it addresses the lastmajor gap in the literature of WW2 cryptography and most likely the last major gapin the literature of WW2.

The IJA and IJN in fact made little use of codes based on a Latinised alphabetwith which most of their thousands of radio operators would have lacked familiarity.Just as Morse code was invented to enable plain language messages written in the26-letter alphabet to be converted into radio signals, the Japanese devised KanaMorse for the same purpose in relation to the use of Kana syllabary for writingJapanese. Both types of Morse had capacity for transmitting the ten digits 0, 1, 2,3, 4, 5, 6, 7, 8 and 9. In the code books used by the IJA and the IJN for their majorcipher systems, plain language entries in these were matched with code groups (or‘words’) that were purely numerical—3-digits long for some simple codes, 4-digitslong in others and, in the case of the all-important JN-25 naval ciphers, all of length5 digits.

Having numerical code groups made it possible to employ a second-stageencryption process before transmission. This process concealed each code groupin a message by combining it with another group of the same length selected froma second book, called here the additive table, according to prescribed rules. In thisbook, the code book taken with its superencryption process is called an additivecipher system and much of the book is directed to an explanation of the proceduresused to decrypt intercepts of messages sent in such systems. The code books andencryption systems were normally changed every few months. Numerous minorsystems were used as well.

In particular, this book explains why JN-25, the principal series of operationalcipher systems used by the IJN, was broken almost immediately after its introduc-tion and continually thereafter. It was the sole source of highest-level Allied SignalsIntelligence in the Pacific throughout 1942 and was providing some 60 % of thisas late as mid-1944. This fact demands explanation, given that all the principaloperational cipher systems used by the IJA were of a type similar to JN-25 butdefied attack until mid-1943, when one important such system was broken. The

Preface ix

others remained unreadable until early 1944 when capture at Sio in New Guinea ofa full set of current code documents transformed the situation.

The explanation is both simple and profound. The IJN used only multiples ofthree for ‘code groups’ in most JN-25 code books. The IJA did not. This bookexposes in considerable detail the disastrous consequences of that IJN practice.

The all-important Signals Intelligence successes obtained from JN-25 and otherearly Japanese cipher systems depended totally on separate decisions made by boththe UK and the USA to develop Signals Intelligence capabilities against Japansoon after the end of WW1. Although these were initially directed at diplomaticmessages, concerns regarding Japanese intentions towards China, South-East Asiaand the Pacific stimulated development of this capacity in the military and navalsectors. The build-up of Japanese naval power was another source of concern. The1930s saw both the UK and the USA setting up teams of cryptanalysts with amathematical and/or scientific background. WW2 was to see the introduction oflarge-scale professional attacks on Axis communications by high-level profession-als with massive (by the standards of the day) data processing facilities and supportstaff.

The cryptanalytic developments explained in this book are based on extensivereading of archival documents held in several countries, including oral historyinterviews, and much published material. Another, totally reliable, source ofinformation used was computer-based experimentation. This is identified whereverit occurs. Both authors have strong backgrounds in classical mathematics coupledwith initially quite separate interests in WW2 dating back at least 40 years.

Our research generally supports the conclusion that little useful knowledge camefrom JN-25 decryption and decoding prior to the raid on Pearl Harbor in December1941. No support is offered to ‘revisionist’ (conspiracy theories) about the raid.This is not to deny the existence of other intelligence that suggested that there wasa strong possibility that such an attack would happen. Indeed, the extensive diarieskept by Canadian Prime Minister Mackenzie King show that he even tipped the daythat war would break out in the Pacific. The US Army Air Force (predecessor of theUSAF) could have had its planes fully armed in the air over Pearl Harbor and allmajor west coast targets every day in that month but did not.

The interception process was complex enough by itself. It involved a numberof sites around the globe and required the secure and camouflaged transmissionof data to the code-breaking centres. Experience with recording, decrypting andreading messages sent using Morse code and its Japanese equivalent, Kana Morse,was needed to handle messages sent in the Kana system of writing the Japaneselanguage.

While the use of Signals Intelligence to turn an ambush planned by the Japaneseat Midway into the Battle of Midway is well known, the critical role played byAmerican submarines in destroying so many Japanese merchant ships is not widelyappreciated. But Winston Churchill’s The Second World War makes it clear thatJapan would have been defeated by submarine action alone. These ships werecarrying desperately needed raw materials from South East Asia, Malaya and theNetherlands East Indies (now Indonesia) to Japan. The United States Navy (USN)

x Preface

utilised intelligence co-ordinated from analysis of intercepts from several navalcodes (JN-25, JN-40 and JN-11) and the important IJA Water Transport Code. Thislast was often called 2468 after the code group inserted in each signal that showedthat this system was in use. The Central Bureau Technical Records, the principalreport of General MacArthur’s Signals Intelligence unit and now available online atthe National Archives of Australia website, is an important source on 2468.

The Water Transport Code is unique among WW2 ciphers in that a large quantityof translated decrypted traffic transmitted in it has survived. This material is inthe U.S. Archives at College Park, Maryland and includes signal after signal aboutmovement of supplies to various IJA bases. This is in itself an interesting exampleof progressively building up military intelligence, in this case about the strengths ofthe IJA garrisons in various places.

This somewhat one-sided ‘cipher war’ depended on three factors. The first wasthe experience, skill and (in some cases) genius of the senior Allied personnelinvolved, exemplified by the outstanding British codebreaker John Tiltman, whofirst broke JN-25. As already noted, this went back to the long years of prepa-ration. The second was the financial support made available. Perhaps as many as60,000 people were involved in Allied radio and signals intelligence (includinginterception) in WW2. The processes involved had to be and were mechanisedas much as possible. The third was simply stated by William Friedman, the greatAmerican cryptologist, in some lectures to National Security Agency staff in 1959.He noted that while high level US Naval communications security in WW2 wasquite adequate for the time, Japanese Naval communications security was quiteinadequate and the IJN lacked the ‘experience and knowledge’ to rectify it.

The contribution of the Bletchley Park cryptologists to the evolution of the waragainst Germany is by now well known. The successful attacks on the Enigma andthe Lorenz encrypted teleprinter emerge as their two greatest achievements. Thefoundational work on JN-25 is the number three achievement of Bletchley Park.This was followed up by essential collaboration with the Americans in 1941. AlanTuring was involved in this in 1939 and somewhat later developed the statisticaltechniques that were needed to handle both European and Japanese ciphers.

The work by William Friedman and Laurance Safford in establishing andbuilding up American Army and Navy Signals Intelligence capability, respectively,in the 1920s and 1930s was crucial to the ability of both services to develop it rapidlyfrom early 1942 onwards. The Army units at Arlington Hall Station in Virginia,Central Bureau in Brisbane, Australia and a British unit in Delhi, India led the attackon Japanese Army systems. The Naval systems were attacked by both British andAmerican teams up to late 1942, but the Holden Agreement then transferred overallresponsibility to the Americans with some British participation.

The high level Japanese diplomatic machine cipher, named Purple by the Amer-ican Army team (the SIS) that broke it in 1940, provided important intelligence,known as Magic, to the Allies but this was of much more relevance to the war inEurope than to the Pacific War. Hence it is minimally mentioned in this book.

The following books are valuable in understanding aspects of Signals Intelli-gence in the Pacific War.

Preface xi

John Prados in Combined Fleet Decoded and Ed Drea in MacArthur’s ULTRAhave described in detail the great use made of Signals Intelligence by Alliedoperational commanders throughout this war. Michael Smith in The Emperor’sCodes has carefully presented a chronological account in which those involved incodebreaking activities, their locations and achievements are vividly reported, buthe does not examine the cryptanalytical techniques behind their successes. StevenBudiansky’s Battle of Wits gives an account of Allied cryptanalytic successesbut mostly in the European theatre of WW2. Those of the European theatre aremuch better known and understood. This book gives the first reasonably completeaccount of who did what in Pacific War cryptology and why it could be done at all.Comparisons with European and Atlantic cryptology help put this into perspective.

Sydney, NSW, Australia Peter DonovanSydney, NSW, Australia John Mack

Acknowledgements

First and foremost, Ralph Erskine of Belfast must be thanked for numerous directcontributions in addition to his valuable published material on WW2 communica-tions intelligence and associated topics. Lee Gladwin, formerly of the U.S. NationalArchives (NARA), has also earned very special thanks. The following have alsocontributed:

Bob Anderson Peter Freeman (dec’d) Alan RobertsDeborah Anderson David Giordano Donald RobinsonAnna Aquilina Jay Hannon Tim RobinsonGeorge Aspden Peter Hilton (dec’d) Edward SimpsonDesmond Ball David Kahn David Sissons (dec’d)Tim Blue Helen Kenny Michael SmithSteve Budiansky Vanessa Mack Catherine SpencerBarbara Cathers Roy MacLeod John SteeleHugh Clarke Robin Michaelson Dennis TrenerryMatthew Connell Judith Pearson Hilda Treweek (dec’d)Vic Czernezkyj (dec’d) Ian Pfennigwerth Cameron VerrillsJim Donovan Doug Pyle Ian WatsonMargaret Donovan Kim Rasmussen Paul WatsonJim Douglas (dec’d) Jim Reeds Leslie WeatherallJim Franklin Joe Richard (dec’d) James Zobel.

Over time the journal Cryptologia has contributed much to the proper under-standing of WW2. Its editors and the authors of all cited material are alsoacknowledged.

Susan Lagerstrom-Fife, Jennifer Malat, Patrick Carr, Rekha Udaiyar and Kulan-thaivelsamy Karthick are thanked for their advice and assistance in the carriage ofthis book from proposal through to publication.

xiii

xiv Acknowledgements

The technical material in this book has been compiled over 12 years from avariety of sources, of which the long contemporary reports Central Bureau TechnicalRecords and Cryptanalysis of JN-25 are of great importance. The former wasstrongly influenced by the late Professor T. G. Room, whose family has been ofassistance. The latter must have been written by a team, but remains anonymous.

The National Archives of Australia, New Zealand, the United Kingdom andthe United States as well as the MacArthur Museum (Norfolk VA, USA), the USNational Cryptologic Museum Library and the Australian War Memorial ResearchCentre have provided useful assistance and access to various documents of the era.The State Library of New South Wales and the Australian Defence Forces AcademyLibrary were very useful.

Note to the Reader

This book describes a range of issues, some of which are quite subtle. This isinherent in the subject matter: if the methods needed to decrypt so much of theJapanese military and naval communications in WW2 had not been subtle, theblunders that were exploited would not have occurred. In general such matters areconsigned to the notes at the end of the chapters.

We have had four types of potential readers in mind when writing this book—(1)the general reader interested in military history, particularly military intelligence,(2) the more specialised reader familiar with the history of WW2, particularly itsPacific aspects, (3) the reader with general interests in pre-electronic cryptographyand (4) the reader with special interest in signals intelligence in the years 1919 to1945.

Some mathematical experience is necessary in order to understand fully thecryptologic aspects of the cipher war against Japan. Parts I, III, IV, V and VIof this book do not require much mathematical expertise. In particular Part VIgives a general account of the Pacific War with some reference to the rest ofWW2. The technical material is appreciably harder. The reader without the technicalbackground may well find it easier to defer Part II, read Chaps. 8–13 in the order8, 11, 13, 9, 10, 12 later and not try to get much out of Chaps. 14 and 15. Someunderstanding of Chaps. 9 and 10 will at the least give an impression of theseriousness of the error in using only multiples of three as JN-25 code groups.

The more specialised reader will already be familiar with the general backgroundmaterial (Parts I and VI) and will (we hope) find everything except Chaps. 14and 15 comprehensible with some effort. Chapters 14 and 15 are appreciably moretechnical, but the former gives a taste of what high-level cryptology of the era reallyinvolved while the latter shows that the use of multiples of three in JN-25 codebookswas much more insecure than was considered in 1939–1942.

In view of the size of the Pacific Ocean, the background (Chaps. 21–23) are betterread with a globe rather than a paper map to hand.

xv

xvi Note to the Reader

The enthusiastic follower of WW2 signals intelligence will find much of interestthroughout this book.

In view of the widespread misunderstanding of the matter to hand, muchdocumentation is supplied in the form of numbered footnotes throughout the text.Some notes provide further explanation of difficult points.

Acronyms and Abbreviations

1WU (etc) Number 1 Wireless Unit (RAAF)A/T Auxiliary Table (in later JN-25 code books)ATIS Allied Translator and Interpreter Service (Brisbane)AWM Australian War MemorialBP Bletchley ParkBTM British Tabulating Machine CompanyCB, CBB Central Bureau, Central Bureau BrisbaneCBTR Central Bureau Technical RecordsD/F or DF Direction FindingDMI (DNI) Director of Military (Naval) IntelligenceFECB Far Eastern Combined Bureau (Hong Kong, later Singapore)FRUMEL Fleet Radio Unit MelbourneGAT(s) Group(s) As TransmittedGCCS Government Code and Cipher School—now called GCHQGYP-1 Pacific Cryptology section 1 unit in Op-20-G (see below)HMS His Majesty’s ShipHMAS His Majesty’s Australian ShipIBM International Business Machines CorporationIJA, IJN Imperial Japanese Army, Imperial Japanese NavyJICPOA Joint Intelligence Center, Pacific Ocean AreaJN-25B8 Japanese Naval cipher system, series 25, version B, additive 8NAA National Archives of AustraliaNARA National Archives and Records Administration (U.S.)Op-20-G USN radio intelligence unitOTP One-time padRAF Royal Air ForceRAAF Royal Australian Air Force

xvii

xviii Acronyms and Abbreviations

RFP (REB) Radio FingerprintingRI Radio IntelligenceRN (RAN) Royal (Australian) NavySIS (SSA) Signals Intelligence Service (U.S. Army)TNA The (British) National Archives, KewUS8 U.S. Army unit near WEC, DelhiUSN U.S. NavyUSAAF United States Army Air Force (now the USAF)WEC Wireless Experimental Centre (near Delhi, India)W/T Wireless/Telegraph (British usage)WW1 World War IWW2 World War II

Contents

Part I Build Up

1 Communications and Sigint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1 Electric Telegraph and Radio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Early Military Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.3 Cables in the First World War . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.4 Tannenberg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.5 British Naval Intelligence in WW1: Room 40 . . . . . . . . . . . . . . 61.6 Jutland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.7 Diplomatic Intelligence: Zimmermann Telegram . . . . . . . . . . 81.8 Army Signals Intelligence in WW1 . . . . . . . . . . . . . . . . . . . . . . . . . 101.9 Morse Code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.10 Kana Morse, Roma-ji and the Chinese

Telegraphic Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.11 Baudot Codes, Teleprinters and Teletypes . . . . . . . . . . . . . . . . . . 131.12 Use of Encryption Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.13 The Components of Signals Intelligence. . . . . . . . . . . . . . . . . . . . 151.14 Hollerith Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191.15 IBM Cards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201.16 Encrypted Code Book Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231.17 Restrictions on the Use of Comint . . . . . . . . . . . . . . . . . . . . . . . . . . 241.18 Other Sources of Intelligence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251.19 The Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2 Japanese Expansion 1895–1941 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292.1 From 1895 to 1914 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292.2 Japan During WW1 and Its Aftermath . . . . . . . . . . . . . . . . . . . . . . 302.3 Japanese Actions During the 1930s . . . . . . . . . . . . . . . . . . . . . . . . . 312.4 Timperley and Kennedy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

xix

xx Contents

3 The GCCS 1919–1941 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353.1 Early Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353.2 Building Up Sigint Strength Against Japan . . . . . . . . . . . . . . . . . 373.3 Eric Nave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373.4 Japanese Naval Attaché Ciphers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.5 John Tiltman. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403.6 Movement in 1939 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413.7 Alan Turing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423.8 Growth of GCCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443.9 Combined Bureau Middle East . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.10 Kamer 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.11 Japanese Army Ciphers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4 William Friedman and the US Army . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494.1 From Riverbank to Washington 1917–1930 . . . . . . . . . . . . . . . . 494.2 American Black Chamber and Diplomatic Codes . . . . . . . . . . 524.3 The Signals Intelligence Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534.4 Elizebeth Friedman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5 Early American Naval Sigint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575.1 The 1920s and the 1930s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575.2 Agnes Meyer Driscoll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595.3 Advanced DF and Interception Bases in the Pacific . . . . . . . . 605.4 The October 1940 Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605.5 Developments in Intelligence Cooperation 1940–1941 . . . . 615.6 Fabian and Friedman on JN-25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

6 Developments in Australia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 676.1 The First Few Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 676.2 The 1919 Jellicoe Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686.3 Infrastructure in Australia at the End of 1936 . . . . . . . . . . . . . . 696.4 Real Expansion: The Period 1937–1941 . . . . . . . . . . . . . . . . . . . . 696.5 Diplomatic Sigint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 736.6 The Coastwatchers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 746.7 Developments in New Zealand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 766.8 The 1947 FRUMEL Commendation . . . . . . . . . . . . . . . . . . . . . . . . 77

7 Preparedness for Attack? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797.1 Incompletely Broken Code Books . . . . . . . . . . . . . . . . . . . . . . . . . . 797.2 Aircraft Versus Warships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 807.3 The Intelligence Build Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 807.4 War with the USA? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 827.5 Relevant Sigint in November and December . . . . . . . . . . . . . . . 847.6 The Haruna Code Destruction Messages . . . . . . . . . . . . . . . . . . . 867.7 The Aftermath: Processing and Distribution

of Intelligence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Contents xxi

7.8 The Aftermath: Naval Comint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Appendix 1 The Mackenzie King Diaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Appendix 2 The 1945–1946 Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Part II Technical

8 Major Encryption Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958.1 Cipher Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958.2 Purple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958.3 The Polish Work on the Early Enigma Machines . . . . . . . . . . 978.4 A Remarkable Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 998.5 Enciphered Teleprinters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1008.6 The Typex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1058.7 The American Sigaba or ECM .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1068.8 Decryption of a Machine Cipher . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078.9 Additive Cipher Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1088.10 Component 1: The Code Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1098.11 Component 2: The Reverse Book . . . . . . . . . . . . . . . . . . . . . . . . . . . 1108.12 Component 3: The Additive Table . . . . . . . . . . . . . . . . . . . . . . . . . . 1108.13 Component 4: The Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1138.14 A Distinction in Additive Table Usage . . . . . . . . . . . . . . . . . . . . . . 1148.15 General Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1148.16 Non-primary Decryption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1158.17 The One-Time Pad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1168.18 The Security of Additive Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 1188.19 Maxims about Cipher Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

9 JN-25 and Its Cryptanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1219.1 The Overall Importance of JN-25 . . . . . . . . . . . . . . . . . . . . . . . . . . . 1219.2 The JN-25 Series 1939–1943 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1229.3 The First Step in Cryptanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1239.4 The Breaking of JN-25 in 1939. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1259.5 Tiltman and the Indicators of JN-25A1 . . . . . . . . . . . . . . . . . . . . . 1269.6 Multiples of Three . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1309.7 Tiltman and the JN-25A Code Book . . . . . . . . . . . . . . . . . . . . . . . . 1329.8 The Probabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1349.9 Phase 1: Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1359.10 Phase 2: Using Known Common Book Groups . . . . . . . . . . . . 1379.11 Patterning and the Use of Multiple Book Groups . . . . . . . . . . 1409.12 Early American Work on JN-25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1419.13 The Switch from JN-25A5 to JN-25B5 . . . . . . . . . . . . . . . . . . . . . 1429.14 Co-operation Between FECB and Op-20-G . . . . . . . . . . . . . . . . 1439.15 The Evolution of JN-25B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1459.16 Joe Rochefort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1479.17 JN-25B in Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

xxii Contents

9.18 Emergency Re-location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1509.19 The Decryption and Decoding of JN-25B8 . . . . . . . . . . . . . . . . . 1529.20 JN-25C and JN-25D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1539.21 The GYP-1 Bible of July 1943 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1549.22 Tailing and Indicator Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1559.23 Later Versions of JN-25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1579.24 JN-11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1579.25 The Real Secret. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

10 Using Common Book Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16110.1 The Lietwiler Letter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16110.2 The Phase 3 JN-25 Stripping Method . . . . . . . . . . . . . . . . . . . . . . . 16310.3 Differences on a Subtractor Machine . . . . . . . . . . . . . . . . . . . . . . . 16710.4 The Method Used by Yeoman Myers . . . . . . . . . . . . . . . . . . . . . . . 16810.5 The GYP-1 Bible on Additive Recovery . . . . . . . . . . . . . . . . . . . . 16910.6 The Dayton Machine on Display in Pensacola . . . . . . . . . . . . . 16910.7 Flags on the Machine? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17110.8 The Real Mistake. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17210.9 Finding the Correct Additive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17210.10 JN-25 at Bletchley Park 1943–1945. . . . . . . . . . . . . . . . . . . . . . . . . 174Appendix 1 Minor Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175Appendix 2 Bayesian Inference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175Appendix 3 Turing and Bayes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177Appendix 4 Contrived Examples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

11 Recovery of a Code Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18111.1 The Rosetta Stone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18111.2 Major George Scovell and Military Intelligence . . . . . . . . . . . 18311.3 Recovery in JN-25 and Similar Systems . . . . . . . . . . . . . . . . . . . . 18511.4 The GYP-1 Bible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18711.5 IBM Machine Assistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18811.6 Machine Decryption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18911.7 Language Officers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

12 Breaking Additive Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19312.1 Breaking the Indicator System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19312.2 Stripping by Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19412.3 Primary Book Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19712.4 A Different Situation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19712.5 Baby Brute Force. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19812.6 Example: JN-25A1 in 1939. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19912.7 Scrambled Row and Column Co-ordinates . . . . . . . . . . . . . . . . . 19912.8 Recovering Page Co-ordinates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20012.9 Brute Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202Appendix 1 Recovering the Primary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202Appendix 2 Another Cipher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

Contents xxiii

13 Making Additive Systems Secure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20713.1 Generalities on Additive Cipher Systems . . . . . . . . . . . . . . . . . . . 20713.2 Disguising, Enciphering and Encoding the Indicator. . . . . . . 20913.3 The Choice of Starting Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21013.4 Alternative Book Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21213.5 Allocating Book Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21313.6 Generating Tables of Additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21413.7 Facilities for Destruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21513.8 Minor Field Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21613.9 Code Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21613.10 Repeated Encipherment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217Appendix 1 Codes Within Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218Appendix 2 Conversion Squares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221Appendix 3 An Anachronism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223Appendix 4 Reducing Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

14 Redundant Encryption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22714.1 The Task of the Cryptologists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22714.2 The CBTR on the WTC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22814.3 The Dependence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23314.4 The Indicators of Cipher 2468 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23314.5 Recovering a New Conversion Square . . . . . . . . . . . . . . . . . . . . . . 23514.6 Tabulating the Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23514.7 Using a Smaller Sample of Intercepts . . . . . . . . . . . . . . . . . . . . . . . 23714.8 Decrypting the Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23814.9 Decoding the Ten Letters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23914.10 The Algebra of Permutations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24014.11 Remark on Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242Appendix 1 Back to the CBTR Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242Appendix 2 Back to Poland 1932 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

15 The Scanning Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24715.1 By-Passing the Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24715.2 Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24915.3 Weakness 1: Alignment and Hall Weights . . . . . . . . . . . . . . . . . . 25015.4 Weakness 2: The Mamba Process . . . . . . . . . . . . . . . . . . . . . . . . . . . 25315.5 Weakness 3: Fourier Decryption . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26115.6 The (Non-historical) NC9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26415.7 Weakness 4: Testing a New Cipher. . . . . . . . . . . . . . . . . . . . . . . . . . 266Appendix 1 Other Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266Appendix 2 A Distribution for JN-11A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268Appendix 3 Mamba-11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268Appendix 4 Thwarting All This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

xxiv Contents

Part III Ciphers and the Submarines

16 Ciphers and the Submarines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27316.1 The Background Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27316.2 Submarines in the Atlantic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27416.3 German Sigint in the Atlantic, 1941–1943. . . . . . . . . . . . . . . . . . 27616.4 Submarines in the Pacific . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27716.5 American Submarines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27916.6 The Sigint Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28016.7 JN-40 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28016.8 JN-11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28216.9 The Water Transport Code 2468. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28316.10 JN-11, JN-25, JN-40, 2468 and Others Together . . . . . . . . . . . 284Appendix 1 The Hellships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

Part IV Organisation

17 Central Bureau 1942–1945 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28917.1 Formation, Early Development and Commitments . . . . . . . . . 28917.2 Assignment to GHQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29417.3 First Steps in Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29617.4 Intelligence Production in the Field . . . . . . . . . . . . . . . . . . . . . . . . . 29717.5 Further Steps in Main Line Solution . . . . . . . . . . . . . . . . . . . . . . . . 29717.6 Photographic Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29917.7 Personnel and Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30017.8 Dissemination of Intelligence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30217.9 Liaison Officers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30217.10 Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30317.11 Forward Movements of Headquarters . . . . . . . . . . . . . . . . . . . . . . . 304Appendix 1 The American Citations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305Appendix 2 Other Citations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

18 Organisation and Reorganisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30718.1 Op-20-G in February 1942 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30718.2 Use Made of Sigint. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30818.3 Communications Security and Deception. . . . . . . . . . . . . . . . . . . 30818.4 Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31018.5 Central Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31018.6 The GCCS in Ceylon and India . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31018.7 US Army Sigint Work 1942–1945 . . . . . . . . . . . . . . . . . . . . . . . . . . 31118.8 Diplomatic and Commercial Intelligence . . . . . . . . . . . . . . . . . . . 31118.9 Postwar Reorganisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

19 Security, Censorship and Leaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31319.1 Sigint on Crete, May 1941 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31319.2 The Churchill Broadcast of 24 August 1941. . . . . . . . . . . . . . . . 314

Contents xxv

19.3 The Capture of NZ Documents in Early May 1942 . . . . . . . . 31519.4 Security Within Australia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31619.5 A Minor Indiscretion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31719.6 The Curtin Leak of April 1942 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31819.7 The Battle of Midway as a Security Leak. . . . . . . . . . . . . . . . . . . 32119.8 The Chicago Tribune Affair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32219.9 The Courier-Mail Affairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32419.10 Cobra and Lagarto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32519.11 The 1944 Presidential Election . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32519.12 Post-War Leaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326

Part V Conclusion

20 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33120.1 General Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33120.2 Acts of Genius? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

Part VI Background

21 From Pearl Harbor to Midway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33721.1 The Onset of Hostilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33721.2 The Japanese Thrust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33921.3 April 1942 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34121.4 The Battle of the Coral Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34221.5 The Sigint Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34421.6 Comint about Midway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34521.7 The Aleutian and Midway Battles . . . . . . . . . . . . . . . . . . . . . . . . . . . 34721.8 Consequences of the Battles of the Coral Sea

and Midway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34921.9 The Burma Campaign, March–June 1942 . . . . . . . . . . . . . . . . . . 35021.10 Events Elsewhere. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

22 Guadalcanal and Papua. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35322.1 Allied Planning in Mid 1942 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35322.2 The Threat to Australia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35422.3 The Battle for Guadalcanal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35522.4 Use of Intelligence in the Guadalcanal Campaign. . . . . . . . . . 35722.5 The Papuan Campaign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35822.6 The Advance Towards Port Moresby. . . . . . . . . . . . . . . . . . . . . . . . 35822.7 Final Victory in Papua . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35922.8 New Guinea and the Wau Campaign . . . . . . . . . . . . . . . . . . . . . . . . 36022.9 The Battle of the Bismarck Sea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36022.10 The Global Situation in Early 1943 . . . . . . . . . . . . . . . . . . . . . . . . . 362

xxvi Contents

23 Rabaul and the Philippines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36523.1 Changes in the Strategic Plans. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36523.2 Cartwheel Commences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36723.3 The Reduction of Rabaul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36923.4 The Western Prong of Cartwheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37023.5 The Coup at Sio, January 1944 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37123.6 Towards the Philippines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37223.7 Developments Elsewhere in 1943 and Later . . . . . . . . . . . . . . . . 374

Recommended Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377