a noncommissioned officer in the navy with a rank comparable to sergeant in the army

Rank intermediate between officer and rating, and in charge of ratings. Usually messed apart from ratings, and has special privileges appropriate to his position.

a crew member who ranks between officer and rating, and is in charge of the ratings

Included gunner's mates, quartermasters, master-at-arms, carpenter, bosun and cooper, the ship's master, chaplain and surgeon