A matross was a soldier of artillery, who ranked next below a gunner.
The duty of a matross was to assist the gunners in loading, firing and sponging the guns. They were provided with firelocks, and marched with the store-wagons, acting as guards. In the United States Army, a matross ranked as a private of artillery.
The word is probably derived from French matelot, a sailor.[1] The OED states that the word is borrowed from the Dutch Matroos ('a sailor of the lowest rank'), and is cognate with similar terms in German, Danish and Swedish.[2]
References
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Matross". Encyclopædia Britannica. 17 (11th ed.). Cambridge University Press. p. 890.