Insignia: Center for Cryptologic History

UNITED STATES CRYPTOLOGIC HISTORY

Pearl Harbor Revisited:
United States Navy Communications Intelligence
1924-1941

Frederick D. Parker

CENTER FOR CRYPTOLOGIC HISTORY
NATIONAL SECURITY AGENCY
1994


Table of Contents

    Introduction

    Earliest Efforts
    Role of ONI
    Early War Plans
    Japanese Fleet Capabilities and Intentions
    Cryptologic Challenge: Navy-Army Cooperation
    Bureaucracy Prevails
    Status Quo in the Pacific
    A New Attempt at Cooperation
    Japanese Cryptography
    Recovering the "Blue Book"
    Introducing JN-25
    Turning Victory into Defeat
    Introducing "Purple"
    Disarmament: Paying the Price
    Confusing Diplomacy
    Struggling for Resources
    Planning for War
    War Games
    Pacific Buildup
    National Emergency
    Circumstances Favor Diplomatic Targets
    Information Gaps
    Cooperation with Allies
    The Move to Hawaii
    Support to the Pacific Fleet
    Japanese Intentions Revealed
    Support to the Asiatic Fleet
    Japanese Strategy
    Japanese Navy
    Diplomatic Messages
    Warning Messages
    Reaction
    Comint After the Opening Attack
    Conclusion

    Appendix A: Naval Messages Intercepted between 5 September and 4 December 1941
    Appendix B: Summary of Diplomatic Messages, July-November 1941
    Appendix C: Highlights from COM-14 Daily COMINT Summary

    Note on Sources
    Bibliography
    Abbreviations


The Naval History & Heritage Command gratefully acknowledges the cooperation of the National Security Agency's Public Affairs Office in allowing this publication to be placed on the internet. The opinions expressed in this publication are those of the author and do not necessarily represent the views of the NHHC.