The United States Army Signal Corps (USASC) is a branch of the United States Army, responsible for creating and managing communications and information systems for the command and control of combined arms forces. It was established in 1860 by Major Albert J. Myer who played a significant role during the American Civil War. It has the initial responsibility for portfolios and new technologies that are eventually transferred to other U.S. government entities. Such responsibilities included military intelligence, weather forecasting, and aviation.

Provides support for the command and control of combined arms forces. Signal support includes network operations (information assurance, information dissemination management, and network management) and management of the electromagnetic spectrum. Signal support encompasses all aspects of designing and installing data communications networks that employ single and multi-channel satellite, tropospheric scatter, terrestrial microwave, switching, messaging, video-teleconferencing, visual information, and other related systems. They integrate tactical, strategic and sustaining base communications, as well as information processing and management systems into a seamless global information network that supports knowledge dominance for Army, joint and coalition operations.

While serving as a medical officer in Texas in 1856, Albert James Myer proposed that the Army use his visual communications system, called aerial telegraphy (or "wig-wag"). When the Army adopted his system on 21 June 1860, the Signal Corps was born, with Myer as the first and only Signal Officer.

Major Myer first used his visual signalling system on active service in New Mexico during the early 1860s Navajo expedition. Using flags for daytime signalling and a torch at night, wigwag was tested in Civil War combat in June 1861 to direct the fire of a harbor battery at Fort Wool against the Confederate positions opposite Fort Monroe. For nearly three years, Myer relied upon detailed personnel, although he envisioned a separate, trained professional military signal service.

Myer's vision came true on 3 March 1863, when Congress authorized a regular Signal Corps for the duration of the war. Some 2,900 officers and enlisted men served, although not at any single time, in the Civil War Signal Corps.

Myer's Civil War innovations included an unsuccessful balloon experiment at First Bull Run, and, in response to McClellan's desire for a Signal Corps field telegraph train, an electric telegraph in the form of the Beardslee magnetoelectric telegraph machine. Even in the Civil War, the wigwag system, restricted to line-of-sight communications, was waning in the face of the electric telegraph.

Initially, Myer used his office downtown in Washington, D.C. to house the Signal Corps School. When it was found to need additional space, he sought out other locations. First came Fort Greble, one of the Defenses of Washington during the Civil War, and when that proved inadequate, Myer chose Fort Whipple, on Arlington Heights overlooking the national capital. The school remained there for over 20 years and ultimately was renamed Fort Myer.

Signal Corps detachments participated in campaigns fighting Native Americans in the west, such as the Powder River Expedition of 1865.