Matrosses first appeared on the establishment in 1639. They were Gunners' Assistants, ie the 'servitor Gunners' or 'inferior Gunners' of former years upgraded and given a more respectable title. Unlike their predecessors they were all on the same rate of pay, somewhat lower than the Gunner's.
The word comes from the German matrossen meaning sailors because the tasks allotted them in action, ie traversing, loading, firing, sponging, manning dragropes, etc, were deemed to be sailors' work. They were less highly trained technically than Gunners.
Matrosses were armed with muskets and bayonets, for their duties included guarding the guns and wagons on the march, and assisting when breakdowns occurred. Later they also took over from the Fusiliers the job of preventing the Drivers running away when the shooting started. (Until 1793 drivers were civilians.)
In 1783 the rank of Matross was abolished, all serving Matrosses being elevated to the rank of Gunner. They had earned it, for their record was no less distinguished than that of Gunners, as the following story typifies:
During the Siege of Gibraltor (1779-83) a shell penetrated the hospital near where a Matross lay injured, and bursting near him took off both his legs. Before he died in great pain he uttered no word except to express his regret that he had not been hit while in action on the gun position.