The Signal Corps in the American Civil War comprised two organizations: the U.S. Army Signal Corps, which began with the appointment of Major Albert J. Myer as its first signal officer just before the war and remains an entity to this day, and the Confederate States Army Signal Corps, a much smaller group of officers and men, using similar organizations and techniques as their Union opponents. Both accomplished tactical and strategic communications for the warring armies, including electromagnetic telegraphy and aerial telegraphy ("wig-wag" signaling). Although both services had an implicit mission of battlefield observation, intelligence gathering, and artillery fire direction from their elevated signal stations, the Confederate Signal Corps also included an explicit espionage function.
The Union Signal Corps, although effective on the battlefield, suffered from political disputes in Washington, D.C., particularly in its rivalry with the civilian-led U.S. Military Telegraph Corps. Myer was relieved of his duties as chief signal officer by Secretary of War Edwin M. Stanton for his attempts to control all electromagnetic telegraphy within the Signal Corps. He was not restored to his role as chief signal officer until after the war.