Marines are the heavy, hardened, and highly-trained fighting force of Starfleet. Their expertise exceeds that of the standard officer in fields such as Diplomacy and Combat. Marines are rarly called upon by Starfleet vessels because the situations usually do not involve conflict, and if they do, it is not usually necessary to call help. The Corps also make many unofficial First Contact missions on planets which are under heavy conflict. These planets remain classified until official First Contact is made.
SFMC is broken into many Divisions, the most known one, the Special Forces Operations Command (SFOPCOM), serving combat tours in the Gamma Quadrant, the Marine Corps of Engineering, Sciences, Secutity, Command Corps and Medial Corps all have troops stationed on board federation ships, to provide that extra hand in the event of an emergency, if the Captain is smart enough to use their expertise.
The Marine Corps is a seperate branch from the Federation, therefore, Starfleet Admirals have no jurisdiction over the actions of the Marines, and cannot give orders and expect somthing to happen. SFMCHQ is located in a remote region of the Northwest Territories of Canada. The base is not open to any visitors who are not enlisted in the Marine Corps, unless given instruction by the Marine General.
All Diplomatic information may be made clear here, as well as non-classified military information will be set forward for other miltaries to view.