Civil War Unit Organization | Regiments, Brigades, Divisions, Corps, Army | Order of Battle

What is a regiment?
What is a brigade?

This presentation outlines unit structure during the American Civil War. Both the north and the south used the same organizational structure.

We will illustrate the organizational structure used in the civil war by example of the 1st Corps of the Army of the Potomac at Gettysburg.

The most basic infantry unit in the civil war is a regiment. Regiments are named by a number and a state. When you hear the designation of a number and a state, like the 19th Indiana, you know that this is a regiment.
Regiments can vary in size. Some regiments have as many as 5 or 6 hundred men, while smaller regiments might be below 200 men. Regiments in the middle range are about 300 men. A colonel will often command a regiment, although when officers are wounded or killed, an officer of lower rank will be put in command. Colonel Samuel Williams commanded the 19th Indiana regiment at Gettysburg.

Regiments can be divided into smaller units called companies. Companies might typically have around 50 men, and they are often commanded by a captain or major. So, a regiment of 300 men may have 6 companies of about 50 men. It is rare for a civil war unit to be separated below company level.

The 19th Indiana is grouped with other regiments. Let's add four more regiments alongside the 19th Indiana. We have the 24th Michigan under Colonel Henry Morrow, the 2d Wisconsin under Colonel Lucius Fairchild, the 6th Wisconsin under Colonel Rufus Dawes, and the 7th Wisconsin under Colonel William Robinson. These five regiments make a brigade. A smaller brigade may have fewer regiments and a larger brigade may have more regiments.

The standard commander of a brigade is the appropriately named "brigadier general," but a colonel of one of its regiments may take command of a brigade if the brigadier general is wounded or killed. At Gettysburg, this particular brigade was under Brigadier General Solomon Meredith, and it was nicknamed the "iron brigade."

Depending on the size of the individual regiments, we may have a brigade force somewhere between 1,500 men to over 2,000 men. Just as regiments vary, so will brigades, because brigades are dependent on the number of men in those regiments.

In front of Meredith's brigade is a second brigade. This brigade is commanded by Brigadier General Lysander Cutler. Cutler's brigade is composed of 6 regiments, the 7th Indiana under Colonel Ira Grover, the 76th New York under Colonel Andrew Grover, the 84th New York under Colonel Edward Fowler, the 95th New York under Colonel George Biddle, the 147th New York under Colonel Francis Miller, and the 56th Pennsylvania under colonel William Hofmann.

We now have two brigades. Multiple brigades form a division. This division is under Brigadier General James Wadsworth. Divisions are large units that may have several thousand men. A brigadier general or a major general may command a division.

Let's add another division to the field. this second division is outlined here is commanded by Brigadier General John Robinson. This highlighted row here is composed of five regiments, which form a brigade under Brigadier General Gabriel Paul. the regiments in this brigade are the 16th Maine, the 13rd Massachusetts, the 94th New York, the 104th New York, and the 107th Pennsylvania.

The second row is another brigade in this division, formed by six regiments: the 12th Massachusetts, the 83rd New York, the 97th New York, the 11th Pennsylvania, the 88th Pennsylvania, and the 90th Pennsylvania.

A third division is shown here. This division is under Major General Abner Doubleday. We can see three rows in this division. The first row is a brigade under Colonel Biddle. He has four regiments in his brigade, one regiment from New York and three regiments from Pennsylvania. The next row is a second brigade, this one under Colonel Roy Stone. This brigade has three regiments from Pennsylvania. The third row is a brigade under Brigadier General George Stannard. This brigade is composed of 5 regiments from Vermont.

These three divisions, composed of a total of 7 brigades, in turn composed of many regiments, form a corps under Major General John Reynolds. A corps is a very large body of thousands of men. Multiple corps make up the Army of the Potomac.

The same unit organization is used for the Army of Northern Virginia.

Film by Jeffrey Meyer
Images from the Library of Congress
Satellite image from Google Maps