Marine Expeditionary Company

A Marine Expeditionary Company (MEC) is a small embarked formation of the UNSC Marine Corps, designed to be attached to a frigate sized vessel of the UNSC Navy. The MEC is air-assault mechanized infantry company of around 200 personnel, as such it is capable of being airlifted and has its own ground transport vehicles.

Mission
The MEC as a quick reaction force for UNSC patrol vessels tasked with patrolling worlds or responding to an armed crisis. Like most Marine formations, the MEC is highly mobile and punchy, but lacking much in the way of support assets. The MEC relies on its home base, the transporting vessel, to handle long range fire support, long range air defense, and repairs and replenishment.

Ground Combat Element
The Ground Combat Element (GCE) was divided up into four platoons:
 * Two Mechanized Marine Platoons, which perform most of the infantry fighting and intelligence-gathering in the field. They are generally subdivided into three small squads of eight to thirteen Marines, with one devoted to heavy weapons, another to a rifleman team, and the last hosting a reconnaissance team who can in a pinch double up as rifle infantry. Each platoon was granted the use of a single armored troop transport, most commonly a M874 Pangolin or M723 Kangaroo, and two M12 Warthogs.
 * One Special Purpose platoon, which follow a similar structure to Mechanized Marine Platoons. Composed of the most elite members of an MEC, Special Purpose platoons are trusted to achieve unorthodox, sensitive goals that require a degree of skill that the regular rank-and-file lack.
 * One armor platoon, which consists of five vehicles: two M808 Scorpion tanks, two M9 Wolverines for air defence, and a single M61 Cougar for scouting missions.

Aviation Combat Element
The Aviation Combat Element consists of the following:
 * 1 D96-TCE Albatross
 * 1 flight of Pelican dropships, for a total of six.
 * 1 squadron of VTOL attack craft, usually AV-14 Hornets, for a total of 12.

Auxiliary Combat Element
In order to reduce manpower size and eliminate the need for bulky equipment, the MEC trades out a logistics combat element in favor of a multipurpose force capable of dynamically swapping from combat to support roles whenever necessary. This normally revolves around the transportation of personnel, supplies, and material, as well as a very basic ability to repair equipment and treat injuries in the field, although the MEC is still reliant on continuous support from their mothership. Among other things, it consists of 12 M12 Warthogs.

History
The Marine Expeditionary Company is a relatively new formation, coming into existence in the closing days of the UNSC-CMA Cold War. It was part of a so-called "No eggs in one basket" doctrine of dividing up ground combat capability among multiple vessels rather that relying on large troop ships and carriers. Though ultimately this fell through as the MEC did not have the long term operational capacity or support elements of a much larger formation and home base. Instead the MEC found use as a singular quick reaction force that can be deployed rapidly anywhere within the system to respond to crisis.

This formation saw fantastic success during the Insurrection, as the MEC was found to be of perfect size, strength and reactability to crush flares of insurgent activity. As the UNSC was not fighting a near-peer opponent, there was significantly less risk of retaliation in force against the home base frigate, allowing the aforementioned vessel to closely partake in operations with its company.

Come the Human-Covenant War however, with the role of the UNSC being the clear underdog on the conflict, the faults of the MEC had once again become clear. Targets of opportunity for the formation were few and far between, given that the Covenant were a vastly superior opponent both in numbers and technology - and with the rapid loss of vessels with the UNSC Navy, MEC formations were being disbanded so that frigates could be pressed into the role of pure fleet warships.

As the UNSC adapted to their new foe, the MEC evolved both in composition and employment. By 2531, it was deployed tactically as a rapid maneuver force that could quickly exploit breakthroughs and weaknesses within enemy lines. Even by the end of the war, some frigates still contained an embarked MEC formation, albeit with largely mismatched equipment and fluid force composition, as wartime attrition had become a major issue for the UNSC.