The Federation's Fleet Marine Forces (FMF) were combined general and special purpose forces within the United Federation Marine Corps that performed expeditionary warfare, planetary landing operations, fighter operations, and ship boarding actions from Starfleet vessels.
The FMF provided Starfleet with a responsive force that could conduct operations in any spectrum of combat.
A four-star General commanded the combined Fleet Marine Forces, answering directly to the Commandant.
As of 2376, there were three operating forces:
Fleet Marine Force, Alpha Quadrant - headquartered at Starbase
Fleet Marine Force, Beta Quadrant - headquartered at Starbase
Each FMF is normally commanded by a Lieutenant General and was either an Infantry Officer or an Aviation Officer. His Executive Officer was required to be from the opposite branch. The smallest unit of an FMF was the Marine Expeditionary Unit.