A platoon sergeant at the Officer Candidate School at Marine Corps Base Quantico, Virginia, a base dedicated to training, educating, evaluating and screening candidates for the United States Marine Corps. In the Marines, the billet of platoon sergeant is usually held by a staff sergeant (E-6) or a gunnery sergeant (E-7), depending on the type of platoon. The sergeant's duties include taking care of the Marines and the platoon's operational control and advising the platoon commander.Photograph: John Kennicutt, U.S. Marine Corps