The Signal Corps: Battlefield Communication–Civil War

Battlefield communication has always been difficult. Before technology, armies relied on bugles, trumpets, drums and banners to signal to the soldiers and to more distant regiments what was to come next.  

These methods continued to be used during the Civil War, but a new type communication system was introduced as well. The new method used flags (and sometimes torches) to communicate across distances.

The process wasn’t simple. The Signal Corps was created in 1860 to implement communication system. The men needed to carry flags, torches, and a disc “dial” system that could change the cipher as needed so that the code could not be hacked.

They also needed a pre-built lookout tower from which to send their signals.

The Signal Corps

The flag system for sending signals was created by Albert James Myer (1828-1880). Myer worked in telegraph offices growing up. He was aware that both the Army and the Navy had been looking for improved communication methods. However, the methods attempted had been complex or involved cumbersome equipment. In the early 1850s, there was no agreed-upon system. 

Albert Myer
Albert Myer

Albert Myer went on to medical school and was still captivated by nonverbal ways to communicate. Myer’s thesis involved a sign language that he felt would be useful for the deaf. From this work, he began to develop what he thought might be a manageable system for the military.

Because Myer’s system was created in the 1850s before the country had splintered apart politically, Myer made no effort to hide his work. Though he ultimately fought for the Union, the flag system he worked on was first used by Confederates in the South. Some of his assistants retuned to their home states in the South, taking Myer’s ideas with them.

Use of Flags

The concept of a flag being used to signal troop movement sounds simple enough, but the method Myer developed was actually quite complex, partly because every message needed to be encrypted.

In general, there were three basic flag signals used. A wave to the left signaled “one,” a wave to the right signaled “two,” and a wave forward signaled a break between words or messages. Certain flag waves were determined for each letter of the alphabet so that words could be spelled out. For example:
A is one, two, or 1, 2.
B is one, two, two, one, or 1221.
C is two, one, two 212, and so forth.

Signal Corps
Demonstrating the use of flags.

When spelled out, the messages ranged from “Look to the left and shoot into the bushes” to complex messages concerning future strategy.

Signal Corpsmen often sent several messages, one right after the other.  A gun fired once indicated a first message; two shots indicated the start of a second message, etc.

Any very important message was to be verified. The receiving station was to send back the same message. This process assured the sender that everyone agreed on what the order had been. 

Equipment of the Signal Corps

Signal Corps members carried with them a staff and two flags. During the day the flag color that was most visible was a white flag with a red square but if there was snow on the ground, a black flag was used.

The corpsmen also carried a torch to use for nighttime signaling. When using a torch, the operator placed a second torch at his feet as a reference point to clarify the signals. To better receive messages, members of the signal corps all carried high-powered telescopes.

cipher system

Since both sides based their system on Myer’s idea, they realized that if the enemy could see the signals, they could probably interpret the conversation. One of the tools signal corps members carried was a two-disc device that permitted them to “dial” different codes. By signaling to the recipient what cipher the corpsmen were using, those who needed to would be able to decipher the messages.

How to Attract Attention

The Signal Corps faced some interesting challenges. How does a corpsman attract the attention of someone to whom they want to signal?

A government instruction booklet from 1864 explains that attempts to attract attention “should never be abandoned, until every device has been exhausted; and they should be renewed and continued at different hours of the day and night…”

Signaling for attention ranged from running back and forth to flag waving. [“A Manual of Signals: For the Use of Signal Officers in the Field,” 1864.]

These men often worked in isolated observation towers built for them by the military. By putting the signal corpsmen up high, they were more visible. In areas where the fighting had been going on for a prolonged time, the towers were spaced so that each tower could be seen by the next one. That way messages could travel from tower to tower by relay. If there was no time for building a tower, they would clamber up rocks or climb a tree, or sometimes move out in front of the troops so more people could see them. Mortality was high.

Signaling for attention ranged from running back and forth to flag waving.

“A Manual of Signals: For the Use of Signal Officers in the Field,” 1864.

Other Ways of Communicating

Anyone who has read the Civil War novel, Killer Angels by Michael Shaara, may remember the opening chapter. A lone rider was assigned to scout the military movements of the other side. Because these “spies” rode alone, they were less likely to draw attention of the other army. This way they could report back as to troop movements. 

Tower for Signal Corps. Library of Congress image.

The spies (or scouts if they were in uniform) rode through potential battlefield areas. They noted the topography, observed troop movement, and talked to townspeople to pick up any information the locals had gleaned as to the plans of the enemy.

Military orders were sometimes sent by courier. These written notes sometimes went from brigade to nearby brigade, but often they were sent over much longer distances. These missives generally also went out in an agreed-upon code.

Telegraphs Used in Some Places

The telegraph was introduced into this country in 1835-36. By 1861, a private telegraph company, Western Union, had wired the U.S. from coast to coast.

The system used wires that could carry Morse code signals. The telegraph was so popular that the Signal Corps attempted to arrive in an area and string telegraph wires in advance of any fighting. This permitted them to communicate with the nearest headquarters.

Balloon Surveillance

The military was also beginning to look to the air. Thaddeus Lowe, a self-made aeronautics expert, had been experimenting with big hot air balloons before the war. In July of 1861, Abraham Lincoln appointed Lowe Chief Aeronaut of the Union Army Balloon Corps.

Antietam Signal Corps. National Park Service.

These hot air balloons were primarily used for general surveillance of an area. Lowe or one of his men rode in the basket with a telescope and report back on the enemy. Balloons were also used occasionally during battles. However, they were difficult to transport, so they often couldn’t reach the location in time. In a unique combination of two innovative services, Thaddeus Lowe convinced Union Major General George B. McClellan to permit him to attempt to relay information via telegraph, but from a balloon. In 1862, the Army of the Potomac, led by McClellan, pushed south to the outskirts of Richmond. Working behind Union lines, Lowe guided a tethered balloon up about 2,000 feet in the air where he observed the actions and movement of the Confederates from the vantage point of the balloon. The balloon carried a telegraph with wires that were strung to the ground, so the telegraph operator traveling with Lowe relayed in signals everything Lowe saw.

Very Different Today

Today our military has access to many ways to observe the enemy. From unmanned drones that fly reconnaissance missions to satellite imagery and infrared sensors that detect enemy presence, modern technology permits battles to be plotted by GPS and tracked via computer in ways that earlier military units could not even imagine.


For more about the Civil War, see Elizabeth Thorn: Burying the Dead While Pregnant. Or read about some of the mascots that accompanied the soldiers: Dog Jack, Mascot and Volunteer for the Union Army.

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