Size of Civil War Era Units It is important to understand that most Civil War units in the field were only at anywhere between 20% to 40% of their full strength. Thus, while in theory a company contained 100 men, and would be recruited at that size, by the time they reached the army they'd be down to 60 or so and after the first battle down to 40 or so. The full-strength sizes are given below, so remember to knock them down by 50% or more when reading about units engaged in battles.
Second, due to casualties among the officers, frequently units would find themselves commanded by an officer one or two grades below the rank he should have for the job (e.g., a regiment commanded by a lieutenant colonel or major). Third, keep in mind that in the early stages of the war and in the more remote areas (such as the Trans-Mississippi), unit organizations tended to deviate more from the norm. What follows will is the authorized strengths, not the numbers who were actually in the field.
I. Infantry Units.
The basic unit is the company, commanded by a captain
100 men = 2 platoons = 4 sections = 8 squads
A company has the following officers (commissioned and non-coms):
Captain (1), 1st. Lieut. (1), 2nd. Lieut. (1)
1st Sgt. (1), Sgts. (4) and Corporals (8).
Plus 2 musicians.
When the company was divided into platoons, the captain commanded one and the 1st Lt. the other. There was a sergeant for each section, and a corporal for each squad. The 1st Sgt. "ran" the whole company.
BATTALION and REGIMENT.
Battalions and regiments were formed by organizing companies together. In the volunteers (Union and Confederate), 10 companies would be organized together into a regiment. The regiment was commanded by a colonel. A regiment has the following staff (one of each):
Col.; Lt. Col.; Major; Adjutant (1st Lt); Surgeon (maj.);
Asst Surgeon (capt.); Quartermaster (lieut); Commissary (lieut);
Sgt-Major; Quartermaster Sgt.
There were also volunteer organizations containing less than 10 companies: if they contained from 4-8 companies, they were called battalions, and usually were commanded by a major or lieutenant colonel. The (Union) Regular regiments organized before the war (1st-10th) were 10 company regiments like the volunteers. When the NEW Regular regiments. were authorized, a different organization was used. The new Regular regiments were organized 8 companies to a battalion and 2 battalions to the regiment. Thus new Regular regiments contained 16 companies. These regiments frequently fought as battalions rather than as single regiments. However, often the 2nd battalion could not be recruited up to strength, in which case they fought as a single regiment.
A brigade is formed from 3 to 6 regiments and commanded by a brigadier general. The South tended to use more regiments than the North, thus having bigger brigades. At some times in the war, some artillery would be attached to the infantry brigade: see the Artillery section below. Each brigade would also have a varying number of staff officers.
A division is commanded by a major general and is composed of from 2 to 6 brigades. In the North usually 3 or 4, but in the South normally 4 to 6. Thus, a Southern division tended to be almost twice as large as its Northern counterpart, if the regiments are about the same size. At some times in the war, some artillery or, less often, cavalry might be attached: see the Cavalry and Artillery sections below. Each division would also have a varying number of staff officers.
A corps is commanded by a major general (Union) or a lieutenant general (Confederate) and is composed of from 2 to 4 divisions. Again the North tended to have 2 or 3, while the South had 3 or 4. Each corps would also have a varying number of staff officers.
Corps within a geographic department were aggregated into armies. The number of corps in an army could vary considerably: sometimes an army would contain only 1 corps and other times as many as 8. Armies were commanded by major generals in the North, and usually by full generals in the South. Corps and armies usually had some artillery and cavalry attached: again, see below. Each army would also have a varying number of staff officers.
To summarize, the nominal strengths and commanding officers were:
UNIT MEN Commander Example NAME
Company 100 Captain Co. A (but not J, looks like I)
Regiment 1000 Colonel 38th N.C. Infantry
Brigade 4000 Brig Genl 3rd Brigade (US) **
Division 12000 Maj. Genl Pender's Division (CS) **
Corps 36000 Maj. Genl* IIIrd Corps (US) **
Army Maj. Genl+ Army of Northern Virginia (CS) ++
* or Lieutenant General in the South
+ or General in the South
** Numerical designation was used in the North, the Commander's name was typically used in the South, e.g. A. P. Hillís Corps.
++ The South mainly used the name of the area or state where the army operated. Rivers were used primarily as names in the North, e.g. Army of the Cumberland.
COMPANY or TROOP.
The basic unit is the troop or company, organized pretty much the same way as an infantry company. The nominal strength was 100. If the troop dismounted for battle, 1 man in 4 would stay behind to guard the horses.
BATTALION and REGIMENT.
In the Union volunteers, 12 cavalry troops form a regiment commanded by a colonel. The Confederate Cavalry used a 10 company regiment. Again, the (Union) Regulars had a different organization: in the Regular units 2 troops form a squadron, 2 squadrons form a battalion, and 3 battalions form a regiment. And again, there were groups of 4-8 companies of volunteer cavalry which are called battalions.
BRIGADE, DIVISION, and CORPS.
Initially, each Union cavalry regiment was assigned to an infantry division. The Confederates brigaded their cavalry together. The Union eventually adopted this organization as well. As the war progressed, both sides formed cavalry divisions (again the South took the lead). The North also formed cavalry corps, and the South later also adopted this innovation.
The basic unit of artillery is the battery, which has 4 to 6 guns, is commanded by a captain, and has 4 lieutenants, 12 or so sergeants and corporals, and 120 or so privates. It typically had 4 guns in the South and 6 guns in the North. Batteries were a subdivided into gun crews of 20 or so, and into sections of 2 gun crews, 2 or 3 sections per battery. A gun crew was commanded by a sergeant and a section by a lieutenant.
BATTALION or BRIGADE.
At the start of the war, each side assigned one battery attached to each infantry brigade, plus an artillery reserve under the army commander. By mid-1862, larger organizations were used. The basic unit contained 3 or 4 batteries of artillery; it was called a battalion in the South and a brigade in the North (same unit, just a different name) and it was commanded by a colonel, lieutenant colonel, or major.
After 1862, it was typical for each infantry division to have an artillery battalion attached, and each corps or army to have a reserve of two to five battalions. Each division's artillery usually fought along side the infantry, while the corps/army reserves were used to form the massed batteries. The artillery reserve was commanded by a brigadier general or colonel.
The Union organized some "heavy artillery" units, regiments containing 10 artillery batteries (about 1800 men) which had training both as infantry and as artillerists. They were organized in much the same way as infantry units, but were quite a bit larger to provide enough men to run the bigger guns in these batteries. Originally raised to man the defenses of Washington, in 1864 they joined the Grant's army, and then served more as infantry. Many of these men lost their lives during the Battle of Cold Harbor north of Richmond in the Summer of 1864.
Both sides raised special regiments of engineers. They were organized similarly to the infantry regiments and were expert in building forts, entrenchments, bridges, and similar military construction. They were combatants but usually didn't do any fighting, instead continued to work on construction even when under fire.
Both sides raised special sharpshooter units. The Confederate units tended to be independent companies, but the Union raised two sharpshooter regiments (Berdan's 1st and 2nd US Sharpshooters). These regiments were organized as infantry. Usually they were assigned to skirmish duty, or they would be allowed to roam around the battlefield to find good positions from which to shoot at enemy officers in the rear.
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