From Classic Encyclopedia 1911
MATROSS, the name (now obsolete) for 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 storewagons, acting as guards. In the American army a matross ranked as a private of artillery. The word is probably derived from Fr. matelot, a sailor.