The public disclosure of Anglo-American signals intelligence since the Second World War, with particular reference to Ultra and Magic

• Main Author: Anderson, R. M.
• Published: University of Cambridge 2005
• Subjects: 907.2
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596093

The puzzling absence of signals intelligence (SIGINT) from the historiography of World War II for nearly three decades continues to reverberate for historians. This thesis aims to explain how and why SIGINT was protected from public disclosure during and after the war, how it became public in 1974, and how WWII historiography has evolved as a consequence of these revelations. Drawing on a vast range of published sources, interviews and recently available archival and electronic-database material, this thesis is comprised of five chapters. With a brief overview of important precedents, the first chapter traces Pacific theatre SIGINT disclosures from WWII through its early and detailed, although not complete, disclosure during the Pearl Harbour hearings and beyond. The second chapter examines how and why the Ultra secret was kept, despite the belief of the gatekeepers that it would soon be discovered by historians analysing operational details and battlefield decisions. The third chapter reviews chronologically the not insignificant Ultra-related disclosures that went unnoticed by historians prior to the publication of F. W. Winterbotham’s <i>The Ultra secret </i>in 1974. The fourth chapter presents the most complete explanation to date of why Winterbotham was allowed to publish, including a review of important precedents. The fifth chapter follows WWII historiographical development through to the end of the century as Ultra disclosures changed the understanding of the war in Europe and rejuvenated historical interest in Pacific theatre communications intelligence. Finally, an epilogue offers several Cold War historiographical comparisons that provide insight in to Anglo-American SIGINT disclosure and historical understanding of intelligence.