Sergeant Major of the Marine Corps is a billet position of the UNSC Marine Corps. Only Sergeant Majors can be selected to hold the billet, and it is technically a staff non-commissioned officer rank. The Sergeant Major of the Marine Corps is equal to the rank of Master Chief Petty Officer of the Navy, Sergeant Major of the Army, and Chief Master Sergeant of the Air Force.
The Sergeant Major of the Marine Corps is selected by the Commandant of the Marine Corps. The SgtMajMC is the senior enlisted member in the Marine Corps, with a 3-star protocol equivalency. The SgtMajMC represents the entire Marine Corps enlisted force, and speaks on behalf of the enlisted members of the service to Marine Corps and UNSCDF senior leadership.