Organization and Rank
A Civil War army consisted of many small parts that were joined together in stair-step fashion to make larger units. There were six basic units of organization. The smallest was a company, which had around 100 men. The largest was an army, which could have many thousands of men.
A company was the basic unit in a Civil War army.
A company had approximately 100 men and was commanded by a captain.
Companies were named with the letters A–K
(J was not used because it looked too much like I.)
A regiment usually contained ten companies.
A regiment had approximately 1,000 men and was commanded by a colonel.
If the unit had only four to eight companies, it was called a battalion rather than a regiment.
A brigade contained an average of four regiments.
A brigade had approximately 4,000 men and was commanded by a brigadier general.
Union brigades were named with numbers, but Confederate brigades were often named after their current or former commanding officers.
A division contained three to five brigades.
A division had approximately 12,000 men and was commanded by a major general.
Confederate divisions tended to contain more brigades than their Union counterparts. Confederate divisions often had twice as many men as Union divisions had.
A corps contained an average of three divisions.
A corps had approximately 36,000 men and was commanded by a major general (Union) or a lieutenant general (Confederate).
An army comprised from one to eight corps.
An army was commanded by a general.
The Union often named its armies after rivers or waterways, i.e., Army of the Potomac. The Confederacy named its armies after states or regions, i.e., Army of Northern Virginia.