The objective of this book is to provide an authentic and reliable guide to U.S. communications intelligence (COMINT) during World War II. A complete history of this subject would be an overwhelming task; therefore, I have limited this effort to matters of high-level policy, administration, and organization, I have tried to show how communications intelligence was controlled and directed by each service and how these services related to each other and to their British counterparts. This is not a history of cryptanalysis or COMINT operations, nor is there much here about the specific uses made of COMINT. Nevertheless, within these limits, l have tried to be complete. That is, I have made an effort to show not only how Army and Navy COMINT activities were run but also how COMINT was structured in the Coast Guard, FBI, and Federal Communications Commission {{FCC). There is also a great deal here on the non-COMINT producing agencies - the Military Intelligence Service (MIS) and the Office of Naval Intelligence QONI). In fact, my account as it relates to the Army has more to do with the MIS than with Arlington Hall, I hope the reasons for this will be made clear in the text, Much of this study seems to be concerned with service politics and interservice disagreements. I can only say that I recognize that COMINT was often produced in spite of certain high-level maneuverings. On that same theme, I also recognize that the people who produced the real COMINT product are, in this study, quite secondary figures, There is little here about Frank Rowlett, Solomon Kullback, or Frank Raven. A word about the British. This study could almost be subtitled "The Development of a COMlNT Alliance." The emphasis on British intelligence is an absolute must for a policy and administrative history, because there is no understanding of the development of U.S. COMINT without continually reporting and examining the role of the British. The sources used in this book are adequately identified in the footnotes and the sources section. I have used the footnotes to report a great deal of supplementary information, and I hope that the reader will turn to them.