Union Hospital Steward, Army of the Potomac, 1863
Each regiment was authorized to have one hospital steward, who was often chosen by the regimental surgeon from the enlisted men in the unit. They were non-commissioned officers who ranked on the same level as a sergeant major.

Army regulations specified that men selected as hospital stewards had to be of good character: "temperate, honest, and in every way reliable, as well as sufficiently intelligent, and skilled in pharmacy." Temperance was an important quality since one responsibility of the hospital steward was controlling and dispensing medicinal whiskey. As he was responsible for keeping many medical records, the steward also needed to be literate and intelligent.

His other duties included assisting the field surgeon in operations, supervising hospital cooks and nurses, and even prescribing drugs and performing minor operations during emergencies. One of his jobs was to carry the medical knapsack into the field, so the surgeon could have medical supplies immediatly at hand. Army doctors relied heavily on hospital stewards for the day-to-day management of their department.

Regulations called for Union hospital stewards to wear the red-trimmed uniform of artillerymen. Their uniform insignia, authorized in 1851, consisted of an emerald green, yellow-edged, half-chevron that bore a two-inch-long yellow caduceus (staff with two entwined snakes and two wings at the top), the distinctive symbol of the medical profession. Another distinct insignia of the hospital steward was the "U.S." surrounded by braids on top of  their caps. Hospital stewards of volunteer regiments, however, were known to wear a variety of different uniforms and insignia.