Reading through this thread, there is a fundamental distinction that has to be addressed. I am conversant with the Army of the Cumberland, however, the basic principles apply.
The basic building block of Civil War armies was the regiment. Bureaucratically, no matter what duty was detailed, the individual remained on the roles of a regiment. An example is the Pioneer Corps Rosecrans created. Every regiment was ordered to detail men with timber felling, sawyers, bridge building & construction skills to man the Pioneer Corps.
The Signal Corps was created with details. It came up not existence in 1860. Officers with college level educations & steady, often mature, literate men were detailed to the nascent signal units. The official Signal Corps did not become a service branch until 1863. Only 2,500 men served in the official corps. Thousands of men were detailed for a few weeks or the duration.
There were all kinds of details levied on regiments. That is why Capt. Davis, 9th State Regiment, Signal Corps da-da-da is commonly seen.
An artillery artillery, e.g., had a number of artificers. A farrier, harness maker, wheelwright / carriage wright were essential to keep horses & equipment in shape. Six drivers / gun rode the horses. None of those individuals manned the cannons.
Capt Charles Perkins’ was an Army Quartermaster in Nashville & Murfreesboro 1863-64. He was in charge of the very busy depots in those vital logistical centers. His papers document the hiring of every kind of support personnel from washer women, laborers, gandy dancers, teamsters, etc. Those individuals did not serve in the Union military. They were temporary employees.
CSA officers & gentleman volunteer privates brought body servants with them. Unfortunately, there is a profound misunderstanding of what their status was. Enslaved body servants were the personal property of the officer they served. Legally a slave had the same status as the horse, tack, uniforms, weapons & other personal property the officer owned.
Laborers were contracted from their owners. I have copies of documents given to local slaveholders. They follow a set format. The owner is ordered to provide a certain number of male slaves, tools, wheelbarrows & six day’s rations. The laborers were not listed by name.
Union regiments, individual messes, etc., hired laundresses, cooks, laborers etc. In 1860 there were 72,000 slaves living in the counties surrounding Nashville. That was an enormous labor pool to draw on. My g-g-granny’s male slaves left. The women & children stayed home. That was common, men & boys self liberated to work for wages. Of course, whole slave communities self liberated, as well.
The body servants of officers captured at Donelson were conundrum. Legally, they were covered by the fugitive slave act. Legally, they should have been given transportation back south. It was quite a problem, an officer could be sued for the value of a slave he did not return. In the end, the Camp Chase servants were given a choose & none of the chose slavery.
A surprising number of them were freeman. The servants were given physicals. The freemen were about ten inches taller than the slaves. Gives some idea of the diet of even privileged slaves.