A First Sergeant is a rank, an E-8 pay grade, as surjimmy pointed out, but it is not unique to the MP MOS (Military Occupational Specialty). There are First Sergeants in every field in the Corps. It is a senior enlisted rank, equal in pay grade to a Master Sergeant, who also an E-8. The next step for a First Sergeant is Sergeant Major, the Master Sergeants' line go to the Master Gunnery Sergeant rank. These two are at the top of the enlisted ranks in the Marine Corps. The senior most enlisted Marine in the USMC is the Sergeant Major of the Marine Corps, who serves as the Commandant's top enlisted advisor.
A direct answer with regards to your question is "yes". There are First Sergeants who are MP's by virtue of their MOS.
A direct answer with regards to your question is "yes". There are First Sergeants who are MP's by virtue of their MOS.
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