A Matross was the term for a private in a train of artillery (a gunner's mate). One of the soldiers who assisted the gunners in loading, firing, and also sponging the guns to stop them overheating. "They carried flintlocks and marched with store wagons, acting as guards" 
In the earlier years, approximately to 1800, only the term matross was used, while in later years, only the term gunner is used.
- ↑ A Tug on the Thread by Diana Quick pub. 2009