First Sergeant
The First Sergeant is the highest ranked enlisted Marine in a detachment or regiment. The First Sergeant is in charge of all of the Marine enlisted affairs, coodinating with various company and platoon sergeants, and is roughly analogous to the Chief of the Boat. As such they act as a bridge and closing the gap between the enlisted personnel and the Officers.
The rank of a First Sergeant varies from Staff Sergeant (in a platoon strength detachment), Gunnery Sergeant or Master Sergeant in a double platoon or company detachment to Sergeant Major in a regiment. On some ships, the Marine Detachment might have a First Sergeant who is a Sergeant, but that is rare.
The First Sergeant reports to the Marine Commanding Officer or Marine Executive Officer in a detachment setting and Regimental Colonel or the regimental executive officer in a regimental setting.