The Secret War for the Union: The Untold Story of Military Intelligence in the Civil War by Edwin C. Fishel (HC/DJ) *Not Ex-Library as pictured.
At the end of the American Civil War, most of the intelligence records disappeared—remaining hidden for over a century. As a result, little has been understood about the role of espionage and other intelligence sources, from balloonists to signalmen with their telescopes. This book gives a history of Civil War intelligence.