This article is from the U.S. Civil War FAQ, by Justin M. Sanders firstname.lastname@example.org with numerous contributions by others.
[Compiled with the assistance of Stephen Schmidt
<email@example.com> and Dominic J. Dal Bello
(A good source of information is Richard Zimmermann, _Unit Organizations
of the Civil War_.)
First, always remember 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 be the ideal, your mileage
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).
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 regts organized before the war (1st-10th) were 10
company regiments like the volunteers. When the NEW Regular regts. were
authorized, a different organization was used. The new Regular regts were
organized 8 companies to a battalion and 2 battalions to the regiment.
Thus new Regular regts 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
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 5th N.Y. Infantry Brigade 4000 Brig Genl 3rd Brigade (US) ** Division 12000 Maj. Genl Cleburne's Division (CS) ** Corps 36000 Maj. Genl* IIIrd Corps (US) ** Army Maj. Genl+ Army of Tennessee (CS) ++ * or Lt. Gen. in the South + or Gen. in the South ** Numerical designation was used in the North, the Commander's name was typically used in the South, e.g. Forrest's 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.