The rank ensign denoted the most junior of officers whose job was to carry the ensign or flag. They had other duties that are listed in Von Steubenís Bluebook (pp. 139-140). The Dictionary of Weapons and Military Terms
(NY: McGraw Hill, 1973) says ...a commissioned officer in the British army who carried the ensign or flag...p. 152.
The derivation of the term sergeant is from the Latin, servire, meaning to serve. A man who had long service gained a position of responsibility and a measure of authority by virtue of service rather than a commission. (West Point Military History Series, Thomas E. Griess (ed.). (NJ: Avery, 1985) Definitions and Doctrine of the Military Art, p. 44. Therefore a sergeant major would be a very senior enlisted man, also known as an non-commissioned officer. His duties are listed in the Bluebook right after those of the ensign.
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