Wilderness Tavern http://vhs4.vahistorical.org/vhsima...SnedenDiary/Vol4/Mss5.1.Sn237.1.Vol4_0273.jpg - Wilderness Tavern served as Early's Division Hospital at the Battle of the Wilderness. The tavern is located near Locust Grove. Surgeon Edwin Phillips of the 6th Vermont, the surgeon left behind in charge of the Union wounded after the Confederate victory.
The most important thing about "Field hospitals" is they shouldn't be confused with "General Hospitals" established in cities and towns. The field hospitals were temporary. They were set up/organized by brigade and/or division. It was the usual practice for the senior brigade and division surgeons to select the locations for and set up the field hospitals. In my research, I have found field hospitals as close as 1 mile in the rear of the initial line and as far as 5 miles in the rear. Even then, sometimes 5 miles is not far enough to the rear ....depending on where the rear was and where it wound up being, as lines shifted. They were not moved forward - once set up, and the operations underway, they remained in place and usually, if overrun, the whole lot - patients, doctors, nurses, and stewards - were captured. Interestingly, Ive never run across mention of one being moved back either. I suppose once the enemy was that close, they just surrendered.
Think of a Field Hospital as a makeshift treatment location which might have been a warehouse, a barn, a house, a few tents thrown up in haste - or worse. This is the Cunningham Farm which served as Field Hospital for Wofford's brigade at Gettysburg - located almost exactly 1 mile in the rear of West Confederate Avenue, where Wofford's brigade lined up on July 2, 1863.
Most any substantial building was suitable for establishing a field hospital. In most cases, the building itself was not the hospital, but the surrounding outbuildings, barns, grounds, etc. The main building may have been used as an "operating room" and housed a few of the higher ranking officers who were badly wounded, but the majority of the wounded would have been in tents (if any were available) and on the surrounding grounds. Where buildings weren't available, tents and shade trees were the norm. The presence of a spring of cool potable water and/or the nearness of the building to a branch of the creek were advantageous.
The regimental surgeons were usually with their respective regiments and rendered immediate aid on the field. At least until the number of injured required them to move to the field hospital to assist the brigade and division surgeons with operations etc. All the men (officers and enlisted) of the brigade who were wounded were initially treated at the brigade or division field hospital. Whichever side held the field evacuated their wounded as soon as the patients were stabilized enough to transport. Those wounded were removed to the various General Hospitals of that side - sometimes at great distance. Those that could not be transported were consolidated at one location and were cared for by their own surgeons, left behind for the purpose. Wounded prisoners fell into the hands of the enemy, along with a few medical personnel, left behind to care for the wounded as best they could.