According to Article XIV, Revised Regulations of the U.S. Army, 1861, "The Secretary of War selects from the sergeants of the line of the army, who may have faithfully served eight years (four years in the grade of non-commissioned officer), as many Ordnance Sergeants as the service may require, not exceeding one to each military post." Furthermore, "Ordnance Sergeants will be assigned to posts [not regiments] when appointed, and are not to be transferred to other stations except by orders from the Adjutant-General's office." It further states, "When a non-commissioned officer receives the appointment of Ordnance Sergeant, he shall be dropped from the rolls of the regiment or company in which he may be serving at the time." And also, "Ordnance Sergeants are to be considered as belonging to the non-commissioned staff of the post, under the orders of the commanding officer. They are to wear the uniform of the Ordnance Department, with the distinctive badges prescribed for the non-commissioned staff of regiments of artillery; and they are to appear under arms with the troops at all reviews and inspections, monthly and weekly."
"Each military post may have an ordnance sergeant, whose duty it is to take charge of all surplus ordnance at the post. He is enlisted for the position, and belongs to the post, and is not removed when the troops are changed." Hence, there were no "infantry ordnance sergeants" in Union regiments with sky blue chevrons and stars.
Confederate Army Regulations of 1863 quoted the U.S. Army Regulations word for word, save for the section on dress. According to that section, the ordnance sergeant would supposedly wear red trim and chevrons, as the Confederate Army did not have a separate Ordnance Department, and the duties of such fell under the artillery branch of the service.
May 20, 1862, the duties of the Confederate regimental ordnance sergeants were officially spelled out by the chief of ordnance: "Duties of ordnance-sergeants. "First. To obey the direction of the division ordnance officer of the brigade ordnance officer (if the brigade is a separate command) in all relative to care and preservation of arms and duties connected therewith. "Second. To take charge of all supplies, arms, and ammunition of the regiment and make returns of the same according to "Ordnance regulations." Issues to be made on written requisitions approved by the colonel or commanding officer of the regiment; which requisitions are to be filed with his "Return of property.' "Third. To take charge of the ordnance wagon or wagons attached to each regiments, and to see that it always contains at least fifteen rounds per man of the regiment--surplus arms or accouterments to be turned over to the brigade or division ordnance officer. "Fourth. To supervise the condition of the arms of the regiment and get a detail of at least two mechanics to assist him in the necessary repairs to the arms, an account of these repairs to be kept as far as possible against each man of the regiment; repairs to be made on the order of the colonel of the regiment. "Fifth. To take charge of the arms and accouterments of the sick of the regiments in hospitals, which will be kept until the sick are sent to the general hospital, when their arms be turned over to the brigade or division depots. "Sixth. In battle it will be the duty of the ordnance-sergeants to remain with the ammunition wagons and act with the details assigned to them from the regiments, under the orders of the ordnance officer, in supplying the troops with ammunition, collecting arms of the killed and wounded, and securing captured arms and ammunition."
While Union ordnance sergeants were few in number and marked by a distinctive uniform, Confederate ordnance sergeants were as numerous as Confederate infantry regiments, whose colors they may have also adopted.