The Union's Most Famous Spies: The History and Legacy of the North's Top Intelligence Agents during the Civil War

In September 1862, the Union had no intelligence service worthy of the name. It had detectives, scouts, scattered networks of informants, balloons, signal flags, and a great deal of luck, but the federal government did not have a coordinated system, to the extent that military commanders did not know enemy troop strength. By the end of the war, the Union would be running the most sophisticated intelligence operations in American history to that point, utilizing an integrated, all-source, p...