Marines from which country, and in which period? For the Royal Marines in the 20th Century, their duties would resemble that of the Royal Navy officers aboard. In battle, the Marines would man one of the ship's turrets. They would also man an appropriate proportion of the ship's secondary armament and its AA guns. The Marine Band would man the ship's transmitting station, the room from which the fire-control equipment was operated. The Marine officers, much like the RN's gunnery officers, would command the men carrying out these tasks. When not in battle, the Marine officers were responsible for the health and welfare of their men - ensuring that they were fed and housed properly. They would also command their men in carrying out routine maintenance and repair.