The Federation Marine Corps is one of the elite forces of the Federation of Neu Normandie. Formed out of elements of the Imperial Marine Corps, immediately following the declaration of the Federation, there are two main missions for the FMC.
The first mission is that of ships guards. There are Marine detachments on all vessels of cruiser size and above. These ships guards serve in two roles. They guard against mutiny by the sailors; rare now but not uncommon in the days immediately following the withdrawal of the imperial forces. In this role the Marines are billeted between the crew and officers with two Marines in power armor always manning the one hatch that separates officer's country from the crew.
The second role of the ship's guards is to serve in boarding actions. The Marine detachment will both defend against enemy boarding attempts and, much more to their tastes, board enemy ships, capturing them for the Federation.
The second major mission area for the FMC is to secure a planet head on an enemy planet. The transition from space to terra firma is, by far, the most difficult of all military missions. The FMC specializes in dropping to a planet and securing a planet hold which can support the landing of larger Army forces.
The nature of the mission demands that the FMC be equipped with grav vehicles. While grav technology is mindbogglingly expensive, it is the only way to reliably accomplish the mission of seizing a planet head. The FMC uses dropships for follow on forces, primarily logistics and mechs, but the main force will be dropped from low orbit in grav vehicles.
The FMC is task organized into mixed air/space/ground task forces of battalion strength. There are Marine Divisions but they are administrative rather than operational organizations. The divisions are force providers for the fleet and the strike elements.
The basic building block of the combat force is the Marine Planetary Assault Unit (MPAU). The MPAU, (pronounced M-POW), is built around a rifle battalion. To this is attached a command element, an aerospace element and a logistics element. The MPAU is capable of capturing a heavily defended spaceport and holding it long enough for the Army's forces to arrive by drop ship.
The MPAUs serve aboard ship, located close to the action. As such they are often the first force available when a crisis erupts. This fact has resulted in an additional, unofficial, mission being added to the mission set of the FMC's MPAUs. They are often called upon to land on a planet under attack and add some firepower and elite skill to the local defense forces. While this is not an official mission the pragmatic nature of the Corps means that all MPAUs are trained to conduct training of indigenous forces.
The FMC is the go-to force in the most trying of circumstances. When the Federation needs forces on a planet immediately they turn to the FMC and it's aggressive infantry to accomplish the mission, whatever it is.