Tactical or battlefield intelligence became vital to both sides in the field during the American Civil War. Units of spies and scouts reported directly to the commanders of armies in the field, providing details on troop movements and strengths. The distinction between spies and scouts was one that had life or death consequences: if a suspect was seized while in disguise and not in his army's uniform, he was often sentenced to be hanged. A spy named Will Talbot, a member of the 35th Battalion, Virginia Cavalry, was left behind in Gettysburg after his battalion had passed through the borough on June 26–27, 1863. He was captured, taken to Emmitsburg, Maryland, and executed on orders of Brig. Gen. John Buford.

Thomas Jordan was a Confederate general and major operative in the network of Confederate spies during the American Civil War. A career soldier in the armies of three nations, he had previously fought in the Mexican–American War, and in 1868 was appointed as chief of staff of the Cuban insurgent army, which fought to achieve independence from Spain. He resigned in 1870 and returned to the United States, where he settled in New York City. Jordan was also a newspaper editor and author, writing articles about the American Civil War.