So I was rereading Sharpe's Trafalgar, and while I know Bernard Cornwell isn't always the best about some stuff in terms of historical accuracy, I had a couple questions about the use of marines onboard during the Napoleonic wars. What did marines do when they weren't fighting? What happened if their officers were killed? Could sailors become marines? And what was the organizational relationship between marines and sailors? Were they mutually exclusive? Could a ship's officer be named by a captain to be in charge of the marines? Thanks for your help!
Sharpe is fun reading, but not always accurate. Anyhow, I wrote about Marines before and you may be interested in that answer:
But to answer directly, without the link:
What did marines do when they weren't fighting?
Generally speaking, they would have sentry duties, or would be engaged in cleaning or drill (make-work is a thing in any military organization), or to provide unskilled labor for working the ship. Marines could learn seamanly skills, if their major would allow for it, but could not be ordered aloft without their consent.
What happened if their officers were killed?
Their sergeants, then corporals, would take over. But they were always under the ultimate discipline of the captain of the ship and the naval chain of command.
Could sailors become marines?
In theory, I don't see why a sailor couldn't enlist in the Marines between voyages, but I don't think it would be likely. The sailors saw the Marines as partly there to guard them against mutiny, and generally looked down upon the Marines.
what was the organizational relationship between marines and sailors?
Marines formed their own separate "division" within the ship (sailors were divided into watches, then divisions within those) with their own officers. Marines were generally commanded by a captain, who would get a brevet promotion to "major" so that there would only be one captain aboard a ship, and no confusion over chain of command.
Could a ship's officer be named by a captain to be in charge of the marines?
The major of Marines reported to the captain, so if he were incapacitated or killed the captain could name a successor (although command would likely pass to his lieutenant, then on down). The captain had pretty absolute powers over his command anyhow, and could relieve any officer of his duties and confine him to quarters, but doing that without a solid reason would get him in trouble with the Admiralty.