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First Manassas: Order of Battle

Prior to the Civil War the United States only had 16,000 men to fill the ranks in the military. After the Union garrison at Fort Sumter fell to Beauregard's Confederates, President Lincoln, realizing that more soldiers were needed to heal the country, called for additional 75,000 volunteer enlistments in the army. In less than four months the United States Military quadrupled in size. Union General Irvin McDowell, leader of the 37,000 man Army of Northeastern Virginia, commanded the largest Army ever assembled in American history.

Commanding such large forces in times of battle required skill and maneuvering. In order to facilitate organized movement the Armies were broken down into smaller sections. Both the Union and Confederate armies consisted of three branches of service. The Infantry, being the most populous, maneuvered on foot, while the cavalry relied on the horse, and the artillery handled the cannons.

The largest organized section within an army was known as a corps. Comprising of between 10,000 to 20,000 men, corps were not in use until later battles of the Civil War. Within a corps there were two or three divisions of between 6,000 - 8,000 men. Only McDowell's army, not yet large enough to function at a corps level, used divisions as its largest body of individuals. The Confederate armies under Johnston and Beauregard operated in smaller sections known as brigades. A brigade was comprised of three to five regiments numbering from 400- 1,000 men each. Regiments were organized in state localities and given numerical identification. Men, both North and South who joined the armies enlisted at their nearest towns, in which the men were further grouped into smaller units known as companies. These companies consisted of soldiers from the same localities and given alphabetical identification within the regiment. This organizational system of the armies is known as the Order of Battle.