In 1861, the United States Army had an authorized strength of 25,000 officers and men, but actual musters numbered about 16,000. The senior commanders had an average age past seventy, and Winfield Scott, the general-in-chief since 1841, was seventy-five, obese, and could not leave his chair without assistance. Of the 1,100 Regular Army officers active when Fort Sumter was fired upon, nearly 400 resigned their commissions and joined forces with the Confederate States of America. With one-third of the officer corps of the Army and one-fourth of the Navy’s joining the Confederacy, it’s little wonder that the two armies were somewhat similar in organization; all the officers had, in fact, trained with the same manuals, most particularly the one known as Hardee’s Tactics. Its author, William Joseph Hardee, after publishing the manual in 1856, served as commandant of cadets at the U.S. Military Academy until January 1861, when he resigned and subsequently was made a brigadier general in the Confederate Army.
At First Manassas, the initial full-scale conflict to pit members and former members of the U.S. Army officer corps against each other, eight of the thirteen senior Union commanders had never seen combat, whereas twelve of the fifteen Confederate generals were experienced battle commanders, most of them West Pointers. Still, as President Lincoln pointed out to General Irvin McDowell (a longtime staff officer elevated to his first command), who hesitated to do battle until his troops were more “experienced,” both sides in the coming conflict were equally “green.” Confederate General Joe Johnston commented on the outcome of the battle by saying that “whichever army had stood a while longer on that day, the other would have given way.”
The two armies facing each other, the Union Army of the Potomac and what later would be called the Army of Northern Virginia, reflected the general tendency for Confederate armies to be named for the “territory” in which they were organized and for Union armies to be named for principal rivers in their area of operation, among those the James, the Ohio, and the Tennessee. There were at least sixteen Union and twenty-three Confederate bodies known as an “army,” those on both sides often bearing the name of their “Department,” or territorial organization, such as Department of East Tennessee. Among the armies, the next largest designation was a “Corps,” and for the Federals the corps were numbered, whereas for the Confederacy most were known by the names of their commanders, as in “Longstreet’s Corps.” Each corps was divided into at least two numbered divisions (also known by the names of their commanders), which were further broken down into “brigades,” and then into “regiments,” which numbered about 1,000 men each on muster in and were the basic fighting units in most battles. They were made up of “companies” (since for the most part “battalions” were not then designated), which were further divided into “platoons,” and then “squads.” In the Union army, brigades were most often identified by a number whereas in the Confederacy they continued to bear the names of their initial commanders, most notable with the Stonewall Brigade, which retained its name even after General “Stonewall” Jackson moved on to higher commands and was subsequently killed. Exceptions to custom in the Union army were brigades known as “Irish,” “Iron,” and “Vermont,” among others. Regiments, in both armies, were usually drawn from a single area (or ethnic background or occupation, such as firemen in the “11th New York Fire Zouaves”) and bore that name as well as a number, as in 20th Maine or Eighth Georgia. Toward the end of the war, most regiments, through disease, desertion, and battle casualties, were well below their starting strength, since there was little provision at the time for replacements, except by forming new units.
In addition to infantry, there were artillery and cavalry organizations, besides the usual headquarters, quartermaster, engineer, and signal units. Each army corps included an artillery brigade (or battalion in the Confederate Army), which was divided into “batteries,” which were the basic operational units, initially limbering six cannon in the Union Army (four guns by the Spring of 1864) and usually four in the Confederacy. Most often batteries were assigned where needed in battle, combined together into a larger force, or kept in reserve.
The cavalry, which operated more or less independently as the “eyes” of field commanders, was most often formed early in the war at regimental strength, divided into battalions and then into ten or twelve “troops” designated by letters, which were further divided into “squadrons” consisting of two companies, the smallest operational unit in horseback combat. Within a year the horse soldiers were being organized into brigades, then divisions, and finally corps, and being employed as mounted infantry. Then (and forever after), many cavalry forces were popularly identified by the romantic figures that led them, most notably J.E.B. Stuart, Phil Sheridan, John Hunt Morgan, John Buford, Nathan Bedford Forrest, and Wade Hampton, as in “Hampton’s Legion.”