THE COMPANY
A Company is the basic unit of a Civil War infantry organization, and the one that every other unit is built upon. Some companies were recruited from a single area causing the company to have a large group of men from the same general area. While other companies included men from a wide variety of regions. Many Civil War companies in the Union armies began with anywhere from 75 to 125 men.
The average, "ideal" company was formed of 100 men, which equaled 2 platoons, which divided into 4 sections, or 8 squads.
It had the following officers (commissioned and non-commissioned):
One Captain, who commands the entire company.
One 1st Lieutenant, the second in command and in command of the 1st platoon.
One 2nd Lieutenant, the third in command and in command of the 2d platoon.
One 1st Sergeant, the ranking enlisted man in the company. Many of his duties were of a clerical nature, writing reports, taking musters, keeping records and tending to other paperwork. He "ran" the whole company.
Four Sergeants, ranked second, third, fourth, and fifth; two were assigned to each platoon - one for each section.
Eight Corporals, four were assigned to each platoon - one for each squad.
Two Musicians
On average about eighty Privates would complete the ranks of the average recruited company of 100 men.
Keep in mind that most Civil War units in the field were only at anywhere between 20% to 40% of their full strength. Before many units even saw combat they lost men to desertion, disease, and sickness. So, 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 above, so remember to knock them down by 50% or more when reading about units engaged in battles.
Also, due to casualties among the officers, units would often find themselves commanded by an officer one or two grades below the rank he should have for the job (for example:, a regiment commanded by a lieutenant colonel or major)
THE REGIMENT AND BATTALION
Regiments are formed by organizing companies together. In the volunteers, 10 companies would be organized together into a regiment. The companies were designated A, B, C, D, E, F, G, H, I and K. To avoid confusion, the letter "J" was not used due to its sounding like the letter "A" and looking similar to the letter "I". Volunteer infantry regiments were named for the states where they were raised, but they could be assigned anywhere.
The regiment is commanded by a Colonel and has the following staff:
Colonel
Lieutenant Colonel
Major
Adjutant (1st Lieutenant)
Surgeon (Major)
Assistant Surgeon (Captain)
Quartermaster (Lieutenant)
Commissary (Lieutenant)
Sergeant-Major
Quartermaster Sergeant
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.
THE BRIGADE
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.
THE DIVISION
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.
CORPS
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.
ARMIES
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 | NAME |
| Company | 100 | Captain | Company A |
| Regiment | 1000 | Colonel | 21st Missouri Infantry |
| Brigade | 4000 | Brigadier General | 3rd Brigade (US)** |
| Division | 12000 | Major General | Cleburne's Division (CSA)** |
| Corps | 36000 | Major General * | 3rd Corps (US)** |
| Army | | Major General + | Army of Tennessee (CSA)++ |
* 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.
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