The Shadow War Between the States: The History of Union and Confederate Intelligence Operations 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. The government eventually forged an integrated, all-source, professional service that fed the commanding generals daily reports on enemy strength, disposition, morale, and intent. The Union also successfully maintained a network of spies inside the Confederate capital that intercepted enemy signal traffic; read Southern newspapers, and used escaped slaves as sources of intelligence.It was not until 1988, when two career intelligence officers named William A. Tidwell and David Winfred Gaddy and a Lincoln assassination scholar named James O. Hall published Come Retribution: The Confederate Secret Service and the Assassination of Lincoln, that the full scope of Confederate covert operations began to come into focus. The picture that emerged from surviving documents, financial records, pension files, and the kind of careful inference that professional intelligence analysts bring to fragmentary evidence, was startling in its ambition and in its implications. The Confederate Secret Service, it turned out, had been playing a longer and more sophisticated game than anyone had previously understood. In fact, Confederate intelligence operations had begun during the first weeks of the war, and in the autumn of 1864, they were on the verge of planning an operation that, had it succeeded, might have changed the outcome of the conflict entirely.