On the eve of the Civil War, there were few officers of the US Army who had ever seen so much as a brigade gathered together in one place. The Regular Army was tiny and its troops were mostly scattered in small detachments at forts and frontier posts. But with the outbreak of war in 1861, armies of a size never before seen in North America took the field. The largest, the Union's Army of the Potomac, was the creation of Major General George B. McClellan, nicknamed "the Young Napoleon." Despite McClellan's talent for military organization and training, he proved no match as a commander for Robert E. Lee, but the army he built was destined to carry the cause of the Union to victory.

McClellan's organizational scheme for the infantry followed the model established by Napoleon's Grand Army. The basic tactical unit was the infantry corps, composed of three or four divisions, each divided into three or four brigades, plus an artillery brigade, for a total strength of 10,000-15,000 men. The complexity of this organization gave rise to a need for badges and flags that would permit quick identification of units and mark the locations of commanders on the battlefield. In February 1863 Army of the Potomac General Order No. 10 specified distinguishing flags for corps headquarters: blue, swallowtailed, with the number of the corps in red on a white botonee-style cross. Then General Orders No. 53  (May 1863) introduced a standard system for that army. Each corps was allotted a distinctive badge. Distinguishing flags for divisions and brigades, rectangular and triangular respectively, displayed the corps badge. A red-white-blue-green color scheme was devised to give each unit a distinctive flag. For example, a triangular flag with a blue border and a red corps badge identified the third brigade of the first division of the corps. There were also flags for the corps artillery brigade and the corps quartermaster. Finally in 1864 General Order No. 115 replaced the botonee-style cross of the corps headquarters flags with the corps badge.

Other Union armies and military departments adopted similar systems for distinguishing flags, but no Army-wide regulation governing their design was published during the Civil War. Nevertheless, the shoulder sleeve insignia and organizational flags of today's US Army can trace their origins back to these corps insignia and flags.

Each regiment of the Army received a National Color and a Regimental Color. The former was a fringed version of the Stars & Stripes inscribed with the regimental title. For cavalry and infantry the latter was dark blue with the national coat of arms over a scroll inscribed with the title of the regiment. For artillery regiments the Regimental color was yellow with crossed cannons. Several different designs were used for the Regimental Color and many regiments carried a state flag instead.  Regiments also had flank marker flags and these were variable in design. Companies and batteries had general guide flags (guidons), most often of the Stars & Stripes pattern.

See also US Army: Organizational Flags for Field Armies, Corps & Divisions

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Union Armies
Garrison & Headquarters Flags

I Corps
Army of the Potomac
II Corps
Army of the Potomac
VI Corps
Army of the Potomac
IX Corps
Army of the Potomac


XXIV Corps
Army of the James
XIV Corps
Army of the Cumberland
Cavalry Corps
Army of the Cumberland
Corps Flags
United States Colored Troops

Regimental Colors & Flags