This work is the primary source of detailed information on the historical harbor defenses of San Diego harbor, and a must-read for anyone interested in the fascinating military history of San Diego, CA. This comprehensive treatment chronicles the extensive fortifications of this important naval harbor, which reached their apex during World War II. Drawing on many primary sources, this book meticulously describes the various fortifications built by the US Army at Fort Rosecrans between 1896 and 1945. Also treated in impressive detail is the subsequent reuse of many of these fortifications for a variety of fascinating purposes during the post-war period, during the Cold War, and in more recent times. The result is an enthralling and unparalleled view of an otherwise neglected history of San Diego's former harbor-defense infrastructure. As nearly all these San Diego military reservations are still in use by the US Navy, public access to much of this area is restricted. The author worked for 30 years at the Navy research laboratory located on the former site of Fort Rosecrans-first as a Naval Officer and then as a civilian engineer-giving the reader an unparalleled view of these forgotten gun batteries, searchlight silos, fire-control and support structures, as well as their interim and current use by the US Navy and the US National Park Service. This unique and detailed first-hand perspective is as close as the general public can get to visiting most of these notable artifacts. This book is not just a technical history of WWII weapon systems and their supporting infrastructure, but also a guide to where they were located, as well as their current status. The 538-page text is thoroughly supported with footnotes, an extensive bibliography, three appendixes, and over 950 illustrations (black-and-white photographs, detailed maps, and historical blueprints).