 Junior Marines on their first enlistment typically serve two years with the unit before receiving orders to a standard Marine Infantry battalion for the rest of their enlistment.NCO's, SNCO's, and Officers may come from virtually any MOS in the Marine Corps, and are typically have at least four years in the Marine Corps.NCO's and above are considered to be on a career enhancing "B-billet", or Special Duty Assignment, and typically serve three years with the battalion.