This is a list of Union field and company grade officers (colonels, majors, captains, lieutenants) who were promoted to general grades by brevet for their Civil War service. It contains each officer's name, substantive rank at the time of his first brevet promotion to Brigadier General, and the date(s) of his brevet promotion(s).
I produced this list of brevet promotions as a result of queries that I received from readers of the full Generals list. People would write asking why a particular general (often an ancestor) was not listed, and I would explain that there were more than 1,300 officers who were known as "General" but who gained that distinction through brevet promotions. I would further explain that I didn't have the time to extend the initial list to include brevets. Well, eventually I found some time.
A brevet rank was an honorary promotion given to an officer (or occasionally, an enlisted man) in recognition of gallant conduct or other meritorious service. They served much the same purpose that medals play today (our modern system of medals did not exist at the time of the Civil War).
A brevet rank was almost meaningless in terms of real authority. For example, a major who was a brevet colonel collected the pay of a major, wore the uniform of a major, could not give orders to lieutenant colonels, and was only eligible for commands that normally fell to majors. But he was allowed to use the title of colonel in his correspondence.
In addition, there were some unusual circumstances where brevet rank carried authority. For instance, when a force consisted partly of Regular troops and partly of state militia, command would go to the officer with the highest brevet rank (who might neither be the highest ranking regular officer nor the highest ranking volunteer!). This came up during the Mexican War on some occasions, and seems to have been designed to allow Regular officers with brevets (implying experience) to assume command over higher-ranking militia officers who had neither experience nor brevets.
An officer could also claim his brevet rank when serving on court-martial duty. Since an officer cannot be tried by officers ranking lower than himself, using brevet ranks allowed more people to qualify as possible court members.
During the war itself, brevets were very difficult to get and were a sign of valor, but on March 13, 1865, the War Department gave one brevet and sometimes two to nearly every officer on duty with the army. This angered many officers and men, who saw it as trivializing the efforts of men who won brevets in combat. (J.L. Chamberlain mentions this in his memoirs, for instance.)
Like regular ranks, brevets were kept separately for the U.S. Volunteers and the U.S. Army. Thus one man could have four ranks: an actual Volunteer rank, a brevet Volunteer rank, an actual Regular rank, and a brevet Regular rank. Brevets in the Regular army were sometimes used to honor men who had already been brevetted Major General in the Volunteers and could not be brevetted again (in the Volunteers), as no brevet Lieutenant Generals were created during the war (Winfield Scott had been made Brevet Lieutenant General [of Regulars] during the Mexican War).
Brevet ranks were authorized for the Regular Army in the Articles of War of 1806; they were authorized for the US Volunteers on March 3, 1863. Partly as a result of dissatisfaction with the end-of-war brevet giveaway, brevet promotions were discontinued in 1869; although officers who had been given brevets before that date continued to use them. They were reinstated for the Spanish-American war and continued in use until after World War I.
The Confederate army did not award brevet promotions.
There are a couple of comments to make about this. Some brevet promotions were made in the US Army between 1869 and the Spanish-American war for frontier service. An example is Frederick Benteen. Also, brevet promotions were provided for in the Confederate Army regulations, but the only Confederate brevet promotions of which I am aware are a number where enlisted men were promoted to the rank of Brevet 2nd Lt.
I have also been helped by having the Official Records on CD-ROM, available from Guild Press of Indiana
There is also a book which covers this subject in great detail - Roger Hunt and Jack Brown's Brevet Brigadier Generals in Blue which I have not used, because I respect their copyright.
Corrections and comments on the list are very welcome. Please direct them to me at firstname.lastname@example.org