Most Civil War Units in the field varied between 25% to 60% of their full strength. In theory, a full-strength company contained 100 men, but disease, desertion & battle casualties would rapidly decrease their numbers. So while to full strength sizes are given, please remember to decrease those numbers when reading about units engaged in battle.

COMPANY

A COMPANY at FULL STRENGTH consisted of 100 men that would be commanded by a CAPTAIN. A COMPANY would be broken down into the following sub-divisions.

100 men = 2 platoons = 4 sections = 8 squads

BATTALION/REGIMENT

Organizing COMPANIES and together formed BATTALIONS and REGIMENTS. In the State volunteer organizations (Union and Confederate) 10 COMPANIES would be organized together into a REGIMENT . This regiment would have 1,000 men at full strength. In both the Union and Confederate armies, individual states were given the task of raising regiments for the armies. Thus the Regiments would be designated by the number in order or organization followed by their state name. Such as the “19th Tennessee Volunteer Infantry”, or the 125th Ohio Volunteer Infantry. A COLONEL normally commanded these regiments. There were also volunteer organizations containing less than 10 companies, if they contained from 4 to 8 companies they were called BATTALIONS, and usually were commanded by a MAJOR or LT. COLONEL.

REGULAR INFANTRY

The Union Regular regiments organized before the war (1st through 10th) were 10 company regiments in strength like the volunteer counter-parts. But, when theNEW regular army was authorized, a different organization was used. The New regular infantry was organized to 8 companies to a battalion and two battalions to a regiment. Thus, NEW regular regiments contained 16 Companies. These regiments frequently fought as Battalions rather than as a single regiment.

BRIGADE

A BRIGADE is formed from 3 to 6 regiments and commanded by a Brigadier General. So if a brigade had 4 regiments in it at full strength, it would number 4,000 men (not including staff) The South tended to use more regiments than the North. Each brigade would also have a varying number of staff officers.

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. An average Infantry Division might number around 12,000 men at full strength. Occasionally some Artillery or less often Cavalry might be attached.

CORPS

A CORPS is commanded by a MAJOR GENERAL (Union) or a LT. GENERAL (Confederate) and is composed of from 2-4 divisions. Again the North tended to have two or three, while the south would have 3 to 4. So an average Infantry Corps might average around 36,000 men at full strength. Each corps would also have a varying number of staff officers.

ARMIES

Corps within a geographic department was aggregated into armies. The number of corps in an army could vary considerably, sometimes an army would contain only one corps and often 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 Artillery and Cavalry attached. Each Army would also have a varying number of Staff Officers. Armies of the north were named after major river systems, such as:

The Army of the Ohio
The Army of the Cumberland
The Army of the Tennessee

Armies of the South were normally named after geographic areas, such as:

The Army of Tennessee
The Army of Northern Virginia

This information has been generously donated by the: TENNESSEE MUSEUM OF THE CIVIL WAR, CHATTANOOGA, TENNESSEE.