|Unit Designator||Commander||Sub Units||Number of Men|
|Brigade||Brigadier General||2-5 Regiments||2-5,000|
|Division||Major General||10 Regiments||10,000|
|Corps||Lieutenant General||2-5 Divisions||2-50,000|
Platoons were designated by ordinal numbers, First Platoon, etc.
Companies were designated by the letters A through K, skipping the letter J. In Old English script, used by the Army on many official documents, the capital forms for both I and J were written the same way. [The letter J is a late addition to the alphabet and derived from I. There was no J or K in Roman Latin, only I and C. His name was spelled: Iulius Caesar, and pronounced: Yulius Kaisar.]
Regiments were designated by ordinal numbers and a state or US/CS designation, i.e. the 10th New York Militia, the 10th Alabama Infantry, or the 10th US Infantry.
Armies were designated by their primary area of action or responsibility: the Army of Tennessee, the Army of the Potomac, etc.
Other types of units were normally known by the name of their first commander: Hardee's Corps, Thomas' Division, although there was an official ordinal number for them somewhere in the paperwork.
A complete name could be lengthy: 1st Platoon of Company G of the 69th New York Infantry of the Irish Brigade of the Army of the Potomac, more so for Privates than Generals.
A Platoon had one Sergeant, two Corporals and twenty Privates/Recruits.
A Company had one Captain, one First Lieutenant, one Second Lieutenant, and one First Sergeant to control things.
A Regiment had one Colonel, one Lieutenant Colonel, one Major, and a Sergeant Major for line functions.
Larger Units had separate "headquarters companies" dedicated to staff functions that were counted as part of a General's Staff.
The basic combat unit for Civil War era commanders was the Regiment.
State Regiments, the vast majority of all units in the War, were usually recruited from within a geographical area [county/city] of a state. The Regimental Officers were appointed by the Governor of the state, and the Company Officers were elected by the men of the Company.
Later in the War there was some effort to ensure a certain level of fitness of officers, but the average Colonel was as new to military life as every man who served under him.
|First Sergeant||Lieutenant Colonel|
|Sergeant Major||Brigadier General|
Staff Sergeant is the modern name of the Non-Commissioned Officers who had special, non-combat roles: Quartermaster Sergeant, Ordnance Sergeant, etc. They had a "staff", rather than a "line" function, and served in headquarters units.
Brigadier was originally a rank of its own without General added to it.
Major General was originally Sergeant Major General, which is the reason a Major General is outranked by a Lieutenant General.
If you look at the list you can see that Majors were originally Sergeant Major Colonels, in the same pattern used for Generals.
At the beginning of the war there were only 16,000 men in the Federal Army and Major General was the highest rank.
Professional Army Officers were given 'Brevet' appointments two or more levels above their permanent rank, to allow the volunteer units to fill in from the bottom.
This is why George Custer died a Lieutenant Colonel, his General's star was a Brevet rank than ended with the War.
Although dead, George Washington was promoted twice during the Civil War, to facilitate promoting U.S. Grant to Lieutenant General, Washington's final rank, and then to promoting Grant to General.
Washington got another promotion to General of the Armies of the United States during World War I, so that General John Pershing could be promoted to the rank of General of the Army.