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 Service. 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.

U.S. Army (Union) Signal Corps
The "father" of the U.S. Army Signal Corps was Major Albert J. Myer, an Army surgeon with an interest in communications by sign language for the deaf and then in signaling over long distances with lightweight and simple to use equipment. He invented a signaling system using a flag (or a kerosene torch for nighttime use) that is known as wig-wag signaling, or aerial telegraphy. Unlike semaphore flag signaling, which employed two flags, wig-wag required only one, using a binary code to represent each letter of the alphabet or digit. Myer was serving at Fort Duncan, Texas, in 1856 when he wrote to Secretary of War Jefferson Davis and offered his signaling system to the War Department. Although the chief engineer of the Army, Colonel Joseph G. Totten, supported Myer's proposal, it did not include specific technical details and Davis rejected it. When John B. Floyd replaced Davis as secretary of war in 1857, Totten reintroduced Myer's proposal, and in March 1859, a board of examination was formed in Washington, D.C. The board, presided over by Lt. Col. Robert E. Lee, was not enthusiastic about the proposal, judging it suitable only as a secondary means of communications over short distances, but it did recommend further testing.

First chief signal officer
Upon the outbreak of war, Myer returned to Washington and addressed the problem of having no signal personnel. His only option was to persuade officers to be detailed from other assignments, which was not considered satisfactory by Myer or the officers themselves, who feared loss of promotion opportunities. He submitted draft legislation to Secretary of War Simon Cameron in August 1861, proposing that a Signal Corps be established with himself, seven assistant signal officers, 40 warrant officers, and 40 signal artificers to serve as line builders and repairmen. He intended that each division of the Army, which he assumed would eventually comprise 500,000 men, would have dedicated aerial and electromagnetic telegraphy support. Congress adjourned without considering the legislation. That fall, Myer, who in addition to being chief signal officer for the Army, served as chief signal officer of the newly formed Army of the Potomac, set up training facilities for detailed officers and men in Fort Monroe and at Red Hill, Georgetown, Washington, D.C. His latter training camp remained in operation through the Peninsula Campaign and the rest of 1862, a period in which he continued to lobby with Congress and the Secretary of War, now Edwin M. Stanton, to establish a permanent corps.

War organization
Edward P. Alexander, Myer's assistant in testing the wig-wag signaling system, resigned his U.S. Army commission on May 1, 1861, to join the Confederate Army as a captain of engineers. While organizing and training new recruits to form a Confederate signal service, he was ordered to report to Brig. Gen. P.G.T. Beauregard at Manassas Junction, Virginia. He became the chief engineer and signal officer of the (Confederate) Army of the Potomac on June 3.


Confederate Signal Corps

Signal equipment and techniques
Wig-wag signaling was performed during daylight with a single flag tied to a hickory staff constructed in four-foot jointed sections. Flags were generally made of cotton, linen, or another lightweight fabric and were issued in the following sizes:
Codes for the alphabet, digits, and some special characters were as follows for the Union Signal Corps:
Waving the flag continuously from left to right was used to attract attention and to indicate that signaling was about to start. Other special sequences of digits were:

Wave the flag from the vertical position to the ground at the left of the flagman, returning immediately to the vertical position.
Wave the flag from the vertical position to the ground at the right of the flagman, returning immediately to the vertical position.
Wave the flag from the ground on the right to the ground on the left of the flagman, returning immediately to the vertical position. The signal "3" always followed a "2" or "4."
Wave the flag from the ground on the left to the ground on the right of the flagman, returning immediately to the vertical position. The signal "4" always followed a "1" or "3."
Wave the flag directly in front of the flagman to the ground, returning immediately to the vertical position. Wig-wag signaling
Telegraph trains were introduced by Myer to support telegraphy for mobile operations. The horse-drawn wagons carried the telegraph sets and supplies such as reels of insulated copper wire and iron lances, for stringing temporary field lines, a practice called "flying telegraph lines." Each train consisted of two wagons, equipped with 5 miles of wire and a telegraph instrument. The first model train was constructed by Henry J. Rogers, a telegraphic engineer from New York City who had worked with Samuel F.B. Morse in building the first commercial telegraph line between Washington and Baltimore in 1844. Rogers's original telegraph instrument for the train replaced the traditional sending key and sound receiver with a dial indicator, a circular index plate bearing the letters of the alphabet and a pointer that turned to the letter to be transmitted. A similar pointer spelled out the message at the receiving end. Rogers provided a galvanic battery that eliminated the danger of acid spills. This equipment eliminated the need for skilled operators who had to be trained in Morse code. Field trials in February 1862 found that it worked satisfactorily over a test circuit of 2 miles of wire. A board of three signal officers recommended that such a train would be of great use as an auxiliary to permanent telegraph lines.

Telegraph train and the Beardslee telegraph
Since aerial telegraphy was sometimes conducted within the clear sight of the enemy, security was a major problem. The Signal Corps introduced a cipher disc, a simple device that allowed the encryption of text. Two concentric discs were inscribed with letters and their numerical equivalents. The sending and receiving party had to agree on the specific alignment between the two discs, ensuring that both parties had identical alignment. To encipher a message, the signal officer selected an "adjustment letter" on the inner disc and then made this letter correspond with a preselected numerical code or "key number" on the outer disc. The signal officer would typically give the key numbers to the flagmen without revealing the plain text version of the message. Although this method of encryption was primitive by modern standards, there is no record that the Confederates ever deciphered a Union message that had been processed in this manner. A more complex system in which four concentric discs were used was invented by Sergeant Francis M. Metcalf and modified by Captain Lemuel B. Norton, but it did not receive widespread adoption.

Ciphers

First Bull Run
At the Battle of Fredericksburg in December 1862, significant use of the Beardslee telegraph made it possible for Maj. Gen. Ambrose E. Burnside to communicate with the Army through the fog and smoke from the burning town. On December 13, the main day of the battle, signal corpsmen extended a line across the Rappahannock River into the town of Fredericksburg while under fire and Burnside was able to communicate with both of his grand division commanders and his supply base, 7.5 miles away.

Fredericksburg
During the Battle of Chancellorsville in May 1863, the performance of the Beardslee telegraph was so poor that Albert Myer soon decided to replace it. The campaign got off to a bad start because the chief signal officer of the Army of the Potomac, Captain Samuel T. Cushing, was kept in the dark about the plans of Maj. Gen. Joseph Hooker and he could not arrange his signal assets in advance. As the Army advanced, Cushing had insufficient wire on hand and was forced to use untested wire that had been left in the field, supported by iron lances, since Fredericksburg. On April 29, as the Army prepared to cross the Rapidan River, the Beardslee telegraph did not work, probably due to excessive wire length. Captain Frederick E. Beardslee, son of the inventor, was sent to make repairs. He found that the machine had been hit by lightning and was operating erratically. That evening a telegraph reached headquarters from the Ford on the Rapidan at 10:30 p.m., but it was marked (incorrectly) as originating at 5:30 p.m. Maj. Gen. Daniel Butterfield, Chief of Staff of the Army of the Potomac, told Cushing that he was not going to wake the commanding general for any telegram that was five hours late; his repose was "worth more than the commissions of a dozen signal officers." The inadequate wires and the unreliable telegraph caused persistent problems and kept General Hooker isolated from his forces in the Wilderness. On May 1, operators of the U.S. Military Telegraph Service were ordered to replace the Signal Corps Beardslee operators.

Chancellorsville
The Battle of Gettysburg featured the Union Signal Corps in its role of observing the battlefield. The chief signal officer of the Army of the Potomac, Captain Lemuel B. Norton, had field telegraph trains at his disposal, but did not deploy them. On July 1, 1863, a Union signal officer, Lt. Aaron B. Jerome, ascended the cupola of the Lutheran Theological Seminary and the courthouse steeple to observe the enemy's approach and reported to Maj. Gen. Oliver O. Howard. On July 2, the Confederate corps under Lt. Gen. James Longstreet attempted to maneuver into position for an attack on the Union left flank. They were forced into a lengthy counter march, delaying their attack, when they spotted the presence of the Union signal station on Little Round Top mountain and knew that their approach would be reported. During the Confederate assault, the fighting was so heavy that the signal station had to be abandoned until the following day. A plaque commemorating the U.S. Army Signal Corps' contribution to the battle is mounted today on a boulder near the peak of Little Round Top. On July 3, before Pickett's Charge, artillery fire against the Union line was so intense that the signalmen could not use their flags. Captain Edward C. Pierce, a signal officer attached to the VI Corps, acted as a mounted courier to Maj. Gen. George G. Meade's headquarters, despite warnings that he would never make it alive through the firing.

See also

Alexander, Edward P., and Gallagher, Gary W. (editor), Fighting for the Confederacy: The Personal Recollections of General Edward Porter Alexander, University of North Carolina Press, 1989, ISBN 0-8078-4722-4.
Brown, J. Willard, The Signal Corps, U.S.A. in the War of the Rebellion, U.S. Veteran Signal Corps Association, 1896, (reprinted by Arno Press, 1974), ISBN 0-405-06036-X.
Cameron, Bill, "Albert James Myer", Encyclopedia of the American Civil War: A Political, Social, and Military History, Heidler, David S., and Heidler, Jeanne T., eds., W. W. Norton & Company, 2000, ISBN 0-393-04758-X.
Eicher, John H., and Eicher, David J., Civil War High Commands, Stanford University Press, 2001, ISBN 0-8047-3641-3.
Heidler, David S., and Heidler, Jeanne T., "Edward Porter Alexander", Encyclopedia of the American Civil War: A Political, Social, and Military History, Heidler, David S., and Heidler, Jeanne T., eds., W. W. Norton & Company, 2000, ISBN 0-393-04758-X.
Raines, Rebecca Robbins, Getting the Message Through: A Branch History of the U.S. Army Signal Corps, Army Historical Series, Center of Military History, United States Army, 1996, ISBN 0-16-045351-8.
Scheips, Paul J., "Union Signal Communications: Innovation and Conflict", Civil War History, Vol. IX, No. 4 (December 1963).
Sears, Stephen W., Chancellorsville, Houghton Mifflin, 1996, ISBN 0-395-87744-X.