United States Colonial Marine Corps

"These Colonial Marines are very tough hombres. They're packing state-of-the-art firepower, there's nothing they can't handle." ―Burke to Ripley, regarding the USCM (from Aliens)

The United States Colonial Marine Corps (USCMC), commonly known as just the Colonial Marines, is the United Americas' primary "force-in-readiness", founded in 2101.
The National Security Act of 2101 formally established the Colonial Marines and its structure. At its peak in 2165 during the Tientsin campaign, the USCM numbered over 240,000 Marines; by 2179 that number had dropped to 165,000, with a further 50,000 in reserve.
They specialize in force projection, being able to operate independently in environments far from home for extended periods thanks to their technological prowess and sizeable space fleet at their disposal. The Colonial Marines are the successor to the United States Marine Corps and are at permanent readiness for immediate deployment across human-controlled space without any additional reinforcement, training or provisioning.
The Colonial Marines, along with the United States Army, are part of the United Americas Allied Command. The primary duties of the Colonial Marine Corps are to maintain security for all United Americas signatories and at all extraterrestrial colonies that fall under the United America's control, and serve as the vanguard of any major combat operation.
They have fought on more than two dozen worlds, including Tientsin (8 Eta Bootis A III), Helene 215, Linna 349, BG-386, LV-1201, LV-742 and the infamous LV-426 "Acheron".
Enemies that the Colonial Marines have fought against included human rebels, Xenomorph, local lifeforms found on other planets, Yautja, U.P.P personnel, and Weyland-Yutani PMCs.

Organization

The Corps is roughly split between the supporting establishment and operating forces. The former includes recruitment, training, research and development, administrative and logistical duties, while the latter performs combat operations. Approximately 58 percent of Marines are in the operating forces.
The operating forces are divided into four combat divisions and four aerospace wings, along with their required support groups. A fifth combat division and aerospace wing also exist as reserves.

Marine Space Force

All combat forces within the Corps are organized into three Marine Space Forces, which answer directly to US Space Command. Each MSF is given the primary responsibility of security their designated areas, though the realities of space mean these areas frequently overlap, while the practicalities of frontier operations mean forces typical operate in autonomous task forces of regimental size or less.

Aerospace Wing

The Colonial Marine Aerospace Wing is responsible for providing aerospace support and airmobility to a Marine Space Force. The Wing itself is largely an administrative formation; in practice much of its elements are attached directly to a Division as an integral element.
Each Wing is divided into a Drop Group, a Tactical Group, and a Support Group. The Drop Group is assigned to operate with Marine ground elements as dedicated support, and consists of approximately 200 dropships. The Tactical Group is assigned reconnaissance, ground-attack and air superiority missions, and averages six to eight squadrons of AD-19C/D Bearcat and AD-17A Cougar strikeships, along with UD-4 "Cheyenne" dropships and UD-22 "Navaho" gunships. The Support Group is assigned CasEvac, search and rescue, psyops and other miscellaneous operations, and consist of 100 dropships and 30 heavy-lift shuttles.

Divisions

Each Colonial Marine Division is a balanced force of combat, service and support elements allowing for orbital assault and sustained ground operations. The Division is organized around three infantry regiments.

Marine Assault Unit

The Marine Assault Unit, or MAU, is the building block of Colonial Marine combat forces, a reinforced battalion designed for independent deep-space operations far from reinforcement or logistical support. At minimum each MAU has the logistical capacity for thirty days of combat operations.
The MAU is commanded by a headquarters platoon, with a logistics platoon, maintenance company and medical unit attached for non-combat support. Additional combat-oriented support units include a reconnaissance platoon, scout-sniper squad, and a combat engineer platoon. A heavy ordinance company is also attached for heavy fire support and aerospace defense, and can include self-propelled artillery, anti-ballistic and anti-space systems.
Two to four infantry companies provide the heart of the MAU, with each company incorporating support elements such as mortars, anti-tank and SAM missiles that can be distributed among their line platoons. If sufficient starlift capacity is available, an armored company of fourteen tanks may also be attached.
An Aerospace Drop Group and some Attack Group elements are also attached to the MAU, while the number and type of United States AeroSpace Force Fleet units varies according to mission type and size.

Rifle Platoon

The organization of the rifle platoons represents the Colonial Marines doctrine of small, autonomous infantry units capable of independent action on a non-linear battlefield. The platoon commander, a lieutenant, is assisted by one or two Synthetics as technical and scientific advisers, medics and drivers. The platoon is divided into two sections, which are further divided into two squads of four Marines each. Each section is led by a sergeant and includes a driver for the M577 Armored Personnel Carrier. In addition, during Drop operations each section is assigned a UD-4 dropship from the aerospace company team. Including the platoon commander and crews for the dropships and APCs, a full-strength rifle platoon would number twenty-five Marines, though in practice the platoon often operates with fewer personnel.
Organic support weaponry for the platoon includes eight M240 Incinerator Units, eight UA 571-C Automated Sentry Guns, two M78 PIGs or M5 RPGs, eighteen M83 SADAR rockets, and one M402 Multiple-Launch Mortar, along with sufficient sensor equipment to establish an overlapping detection matrix with a frontage of over one kilometer.

Combat Synthetic Platoon

Sometime after bolstering their ranks with the artificial womb (A.W.) soldiers, the Colonial Marine Corps also started to experiment with bolstering their ranks with combat androids, specifically ones that followed the Three Laws of Robotics. Much more cost effective and lower maintenance then their human counterparts these models were seen in action early as 2192. Much more humanistic then previous models, some were known to experience even the most intense human emotions such as falling in love. Still self-aware of their origins, these Synthetic models were precursors to later advanced models.

Squads

The rifle squad consists of four Marines: A Corporal, a Lance Corporal, and two Privates/Privates First Class. The squad is broken up into two fireteams, the Rifle Team and the Gun Team. The Rifle Team consists of two riflemen armed with M41A Pulse Rifles, while the Gun Team consists of a gunner armed with the M56 Smartgun and a rifleman armed with a M41.