icon What is the Corps?

The United States Marine Corps is America’s amphibious force-in-readiness. While that seems like a mouthful, it makes sense because of our country’s position as a maritime nation with worldwide interests. The fundamental mission of the Corps can be simplified as readiness. This mission, combined with the Marine state of mind and culture, makes the Corps what it is today: a national force-in-readiness, prepared in fact and required by law to “perform such other duties as the President may direct,” which means “ready for anything.” Marines and Marine Corps missions have long been associated with the sea and with amphibious operations. The word “Marine” itself comes from the Latin “marinus,” meaning “related to the sea.” The “amphibious” comes from the Greek “amphibion”–literally, “living a double life.” Marines today have a dual responsibility: to remain ready to serve on land, sea, and in the air and to maintain the expert skills required for amphibious operations.

Marine expeditionary forces of all sizes deploy by land, sea, or air. They provide the Nation’s only major capability to forcibly enter any hostile area from the sea. They can proceed without interruption from a naval to land campaign with the ability to build up a strong fighting force. They are a combined force having all elements of combat power. Their versatility and responsiveness lend a significant dimension to the options available to our leaders in time of crisis.

Today’s Marine Corps emphasizes three fundamentals: readiness, versatility, and the totally integrated capabilities of the Marine air-ground team. Operational readiness is the Marines’ top priority. It is the cornerstone of the Marine Corps’ existence as a fighting military organization.

Versatility refers to the Marines’ method of tailoring air-ground teams in size, structure, and striking power to meet worldwide needs. It ensures, too, that Marine forces will remain flexible enough at all times “to perform such other duties as the President may direct,” a mission deliberately expressed in general terms to permit the Marines to respond swiftly, when needed, as a general-purpose force.

The air-ground team originated in the U.S. Marine Corps. Marine aviation operates not just as a support for ground combat elements, but also as a fully integrated component of Marine expeditionary organizations.

So, today, as in the past, Marines must, and do, cast a constant eye seaward … and beyond.


The present structure, missions, and functions of the Marine Corps are set forth in the National Security Act of 1947, amended several times in subsequent years. This act states that the Marine Corps’ minimum peacetime structure shall consist of “not less than three combat divisions and three aircraft wings, and such other land combat, aviation and other services as may be organic therein.” In addition, the Marine Corps maintains a 4th Marine Division (MarDiv) and Marine Aircraft Wing (MAW) in the standing Marine Forces Reserve (MFR).

To carry out its missions, the Marine Corps is periodically authorized personnel strength levels, which will permit it to maintain the forces stipulated by the National Security Act. During peacetime, these strength levels have remained essentially the same since 1953, providing an active duty strength of around 175,000 Marines. In addition, the MFR maintains a strength of approximately 100,000 made up of the Selected Marine Corps Reserve (SMCR), the Individual Ready Reserve (IRR), the Individual Mobilization Augmentee (IMA), and the Active Reserve (AR).

Beginning with their primary mission, the following specified missions have been assigned to the Marines under the National Security Act and its amendments.

The first mission is to provide Marine air and ground forces for service with the fleet as landing forces in the conduct of amphibious operations. This mission reflects the Marine Corps’ statutory role as America’s force-in-readiness and calls into play the full resources of the Navy and the Marine Corps operating together.

To execute an amphibious operation (assault, raid, demonstration, withdrawal) successfully requires special skills and equipment, intensive training, and the highest possible measure of coordination among the many different elements of the amphibious task force (ATF). It is costly, but in addition to its major objectives, it produces a range of other capabilities—to conduct rescue missions or to demonstrate force in a situation that could otherwise escalate into a major crisis.

The second mission is the oldest Marine Corps mission—duty afloat aboard armed vessels of the Navy.

The third mission is to develop in coordination with other services, the tactics, techniques, and equipment for landing forces in amphibious operations. It is a logical extension of the primary mission and establishes a distinct Marine Corps responsibility with respect to the other armed services.

The fourth mission is to be prepared for wartime expansion in accordance with Joint Mobilization Plans. It is common to all the armed services. Simply stated, mobilization plans require the activation of Marine Forces Reserve (MARFORRES).

The fifth mission is to perform such other duties as the President may direct. As noted earlier, this mission was deliberately expressed in general terms in the National Security Act. It permits the President to call upon Marines as a ready force in times of crisis. The Marine Corps is the only one of the armed services assigned such a mission by law.

Organization and Function

The overall organization of the Marine Corps falls into two broad categories: the operating forces and the supporting establishment. Together they comprise more than 90 percent of the total strength of the Marine Corps.

Operating Forces

Marine Security Forces. Marines provide approximately 3,400 Marines to the Marine Corps Security Forces (MCSF), protecting key naval installations and facilities worldwide. Although not assigned to combatant commands, they are part of the operating forces of the Marine Corps. These security forces include Fleet Antiterrorist Support Team (FAST) companies and Marine security force companies in the continental United States (CONUS) and abroad. Formerly made up of dozens of Marine Barracks and Detachments, these declined in number over the years and then reformed in 1986 into MCSF companies, monitored by a single battalion headquarters.

Marine Security Guard Detachments. Under authority of the Foreign Service Act of 1946, the Marine Corps has a collateral mission of providing security guards for American embassies, legations, and consulates. For this duty, the Marine Corps Embassy Security Guard number approximately 1,000 Marines at 174 posts (also known as detachments) organized into 9 regional MSG commands and located in over 135 countries in 18 time zones, as well as its headquarters at Marine Corps Base, Quantico.

Marine Corps Forces. In 1992, Marine Corps “componency” was established, and Marine Corps component commanders, who are referred to as the Commander, Marine Corps Forces (COMMARFOR), were assigned or designated for each of the five geographic combatant commands. The former Fleet Marine Forces, Atlantic (FMFLANT) and Fleet Marine Forces, Pacific (FMFPAC) were redesignated Marine Corps Forces, Atlantic (MARFORLANT) and Marine Corps Forces, Pacific (MARFORPAC), respectively, and assumed the missions and responsibilities of service component commands. Headquarters, Fleet Marine Forces, Europe (FMFEUR), was redesignated Headquarters, Marine Corps Forces, Europe (MARFOREUR). Marine Corps component planning liaison cells were established in Central Command (CENTCOM) and Southern Command (SOUTHCOM). Upon the redesignation of the U.S. Atlantic Command as U.S. Joint Forces Command, the former MARFORLANT became Marine Corps Forces Command (MARFORCOM).

In addition to providing Marine Corps representation to each combatant command, these Marine Corps components have assumed most of the administrative and logistics requirements previously performed by Fleet Marine Forces. This change allowed the Marine Corps units of the air-ground task forces to concentrate on combat operations. The new joint force organization, supported by the activation of Marine Corps components, significantly changed the operational environment in which Marine Corps forces deployed and operated. Marine Corps forces also are provided to naval commands by the Marine Corps component commander, who also may perform the duties of a Fleet Marine Forces Commanding General with the status of a naval type commander. Assignments as a Commander, Marine Corps Forces, and Commanding General, Fleet Marine Forces, have separate, distinct command relationships and missions. For example, Commander, MARFORPAC—the Marine Corps component commander—provides Marine Corps forces to the Commander, U.S. Pacific Command. As the Commanding General, FMFPAC—a naval type commander—Commander, MARFORPAC, provides Marine air-ground task forces (MAGTFs) to the Commander, U.S. Pacific Fleet. The Marine Forces contain ground and aviation combat elements and logistics elements. The largest of these elements are the MarDiv, the MAW, and the Marine Logistics Group (MLG).

Marine Division. The mission of the MarDiv is to execute amphibious assault operations and such other operations as may be directed. The MarDiv must provide the ground combat power to an ATF and conduct subsequent land operations in any operational environment. The division commander fights by using combined arms tactics and tailors the force to the demands of each mission. The division is composed of a headquarters; infantry and artillery regiments; and tank, amphibious assault vehicle, light armored reconnaissance, reconnaissance, and combat engineer battalions, with approximately 18,000 personnel and more than 1,000 combat vehicles.

Marine Aircraft Wing. The MAW is task organized to provide a flexible and balanced aviation organization that is capable of providing the full range of aviation operations in a variety of areas without the requirement for prepositioned support, control, and logistical facilities. The MAW is the smallest unit with the inherent capability of performing all six functions of Marine aviation. The MAW is composed of a headquarters, a control group, a support group and fixed- and rotary-wing aircraft groups, with approximately 18,000 personnel and 350 aircraft. Aviation organizations smaller than a wing can provide the capabilities to accomplish any or all of the six aviation functions by using task organization.

Marine Logistics Group. The MLG is a composite grouping of functional organizations that provide combat service support (CSS) beyond the organic capability of supported units to all elements of the force. In this respect, it is structured to support, in garrison or deployed, a one division/one wing configured force. All elements of the MLG are structured to provide task-organized subordinate elements to support independently deployed battalions, regiments and equivalent organizations, or geographically separated units in garrison. The MLG headquarters provides general and direct support and sustained CSS in all levels of conflict. The MLG includes approximately 9,000 personnel and thousands of pieces of support equipment.

Supporting Establishment

The Marine Corps supporting establishment provides, trains, maintains, and supports the operating forces. The supporting establishment includes: Training and Education Command (TECOM); Training Command (TRNG CMD); Marine Corps Recruit Depot San Diego (MCRD SD); Marine Corps Recruit Depot Parris Island (MCRD PI); Education Command (EDCom); Marine Air Ground Task Force Training Center (MAGTFTC); Marine Corps Systems Command research, development, and evaluation organizations; supply installations; Reserve activities; certain Marine Corps bases, barracks, and air stations; Headquarters Battalion, Headquarters Marine Corps (HQMC); and miscellaneous small activities.

Marine Air-Ground Task Forces

The MAGTF is the principal organization used by Marine Corps operating forces for the conduct of all missions across the range of military operations, both combat and noncombat. MAGTFs are balanced, combined arms forces with assigned ground, aviation, and sustainment elements. They are flexible, task-organized forces that can respond rapidly to a contingency anywhere in the world and are able to conduct a variety of missions. (See Figure 1-1.)

Figure 1-1. MAGTF

Although organized and equipped to participate as part of naval expeditionary forces, MAGTFs also have the capability to conduct sustained operations ashore. A MAGTF provides a combatant commander or other operational commander with a versatile expeditionary force that is capable of responding to a broad range of crisis-and-conflict situations. MAGTFs are organized, trained, and equipped to perform missions ranging from humanitarian assistance to peacekeeping to full-scale combat and can operate in permissive, uncertain, and hostile environments. They may be shore or seabased in support of joint and multinational major operations and/or campaigns. MAGTFs deploy as amphibious, air-contingency or maritime prepositioning forces (MPFs), either as part of a naval expeditionary force or via strategic lift. They can present a minimal or a highly visible presence and are able to project combat power ashore in measured degrees or can provide secure staging areas ashore for follow-on forces. MAGTFs are prepared for immediate deployment overseas into austere operating environments, bringing all means necessary to accomplish the mission. When deployed aboard amphibious shipping, MAGTFs maintain a continuous presence at strategic locations around the globe and can be moved rapidly to and indefinitely stationed at the scene of potential trouble. The MAGTF provides the joint forces commander with the capability of reconstitution, which is the ability of an expeditionary force to regenerate, reorganize, replenish, and reorient itself for a new mission without having to return to its home base. MAGTF operations are built on a foundation of six special core competencies: expeditionary readiness, combined arms operations, expeditionary operations, seabased operations, forcible entry from the sea, and reserve integration.

The primary characteristics of the MAGTF (and of Marine Corps Forces) are summarized thus:

  • Organized, trained, and equipped for combat essential to the prosecution of a naval campaign to seize objectives against the best and most modern equipped enemy.
  • A balanced force of combined arms and services.
  • Primarily trained, organized, and equipped for offensive employment.
  • Adaptable to the active defense of advanced naval bases.
  • Trained, equipped, and ready for prompt and effective employment in any climate or terrain.
  • Trained and equipped for airborne operations as required, in accordance with policies and doctrines of the Joint Chiefs of Staff.
  • Provided with sufficient organic CSS capability to establish and sustain combat power in the execution of normal missions and capable of supporting—
    • Supply.
    • Maintenance.
    • Transportation.
    • Deliberate engineering.
    • Services.
    • Health services.
  • Provided with organic aviation units primarily organized, trained, and equipped to operate in conjunction with ground units in amphibious operations and capable of performing—
    • Offensive air support (OAS).
    • Antiair warfare (AAW).
    • Assault support.
    • Air reconnaissance.
    • Electronic warfare (EW).
    • Control of aircraft and missiles.

Although MAGTFs are task organized, each has the same basic structure, regardless of its size or mission. A MAGTF has four core elements: a command element (CE), a ground combat element (GCE), an aviation combat element (ACE), and a logistics combat element (LCE). The CE is the MAGTF headquarters. It is task organized to provide command and control capabilities (including intelligence and communications) necessary for effective planning, direction and execution of all operations. The GCE is task organized to conduct ground operations in support of the MAGTF mission. It is normally formed around an infantry organization reinforced with requisite artillery, reconnaissance, armor, and engineer forces and can vary in size and composition from a rifle platoon to one or more MarDivs.

The ACE is task organized to support the MAGTF mission by performing some or all of the six functions of Marine aviation. The ACE is normally built around an aviation organization that is augmented with appropriate air command and control, combat, combat support, and CSS units. The ACE can operate effectively from ships, expeditionary airfields or austere forward-operating sites and can readily and routinely transition between seabases and expeditionary airfields without loss of capability. The ACE can vary in size and composition from an aviation detachment with specific capabilities to one or more MAWs.

The LCE is task organized to provide the full range of CSS functions and capabilities needed to support the continued readiness and sustainability of the MAGTF as a whole. It is formed around a LCE headquarters and may vary in size and composition from a support detachment to one or more Marine Landing Groups (MLGs).

Marine Expeditionary Force

The Marine expeditionary force (MEF) is the principal Marine Corps warfighting organization. It is capable of missions across the range of military operations, through amphibious assault and sustained operations ashore in any environment. With appropriate augmentation, the MEF CE is capable of performing as a joint task force (JTF) headquarters. There are three standing MEFs: I MEF, based in southern California and Arizona; II MEF, based in North and South Carolina; and III MEF, based in Japan and Hawaii. Each standing MEF consists of a permanent CE and a MarDiv, MAW and MLG.

Marine Expeditionary Brigade

The Marine expeditionary brigade (MEB) is used for missions across the range of military operations, through amphibious assault and sustained operations ashore in any environment that does not require the combat power or sustainment of a MEF. With appropriate augmentation, the MEB CE is capable of performing as a JTF headquarters. The MEB is built around a reinforced regiment, a Marine aircraft group (MAG) and a combat logistics regiment (CLR). The MAG will contain all types of aircraft required by the mission. Presently, the MEB CEs remain cadred in the reserve or encapsulated in the MEF CE organizations, to be activated when required for a specific mission. As with the Marine expeditionary unit (MEU), below, they are even-numbered when organized in the Atlantic and odd-numbered in the Pacific theaters.

Marine Expeditionary Unit (Special Operations Capable)

The Marine expeditionary unit (special operations capable) (MEU(SOC)) is the standard forward-deployed Marine expeditionary organization. MARFORCOM and MARFORPAC deploy forward-deployed MEU(SOC)s
to the Mediterranean Sea, the western Pacific and the Indian Ocean or Arabian Gulf region. The MEU(SOC) can be thought of both as a self-contained operating force capable of missions of limited scope and sustainment and as a leading element of an entire MEF. The MEU routinely receives special training before deploying that results in it being designated as “special operations capable.” To receive the certification, the entire organization undertakes an intensive 26-week, standardized predeployment training program that includes a qualifying exercise and a final evaluation. The MEU must demonstrate competence across the entire spectrum of required capabilities, be able to plan and execute any assigned mission within six hours of notification and conduct multiple missions simultaneously. The MEU receives selected personnel and equipment as required to provide enhanced conventional and selected maritime special operations capabilities. There are seven standing MEU(SOC) CEs. Residing within I MEF are the 11th, 13th, and 15th MEU(SOC)s; residing within II MEF are the 22d, 24th, and 26th MEU(SOC)s; residing within III MEF is the 31st MEU(SOC). Although each MEU(SOC) is task organized, a typical MEU(SOC) includes:

  • A permanent CE.
  • An infantry battalion reinforced with artillery, reconnaissance, engineer, armor, assault amphibian units, and other detachments as required.
  • A reinforced helicopter squadron with transport, utility and attack helicopters, a detachment of vertical/short takeoff and landing (V/STOL) fixed-wing attack aircraft, and other detachments as required.
  • A task-organized LCE.

Special-Purpose Marine Air-Ground Task Force

A special-purpose MAGTF (SPMAGTF) is a MAGTF temporarily formed to conduct a specific mission. It normally is formed when a standing MAGTF is either inappropriate or unavailable. SPMAGTFs are organized, trained, and equipped to conduct a wide variety of missions ranging from crisis response, to regionally focused training exercises, to peacetime missions. Their SPMAGTF designation derives from the mission they are assigned, the location in which they will operate, or the name of the exercise in which they will participate (e.g., “SPMAGTF (X),” “SPMAGTF Somalia,” “SPMAGTF UNITAS,” “SPMAGTF Andrew,” etc.). A SPMAGTF may be any size, but normally it is the size of a MEU (or smaller) with narrowly focused capabilities chosen to accomplish a particular mission. It may be task organized deliberately from the assets of a standing MEF or may be formed on a contingency basis from an already-deployed MAGTF to perform an independent, rapid-response mission of limited scope and duration. By definition, SPMAGTFs include all four of the basic elements of a MAGTF.

Disposition and Readiness

Headquarters, Marine Forces Command (MARFORCOM) is located in Norfolk, Virginia. Its major units comprise the II MEF, headquartered at Camp Lejeune, North Carolina. The MEF has three major subordinate commands (MSCs): 2d MarDiv; 2d MLG, both headquartered at Camp Lejeune; and 2d MAW, headquartered at Marine Corps Air Station (MCAS), Cherry Point, North Carolina.

Headquarters, Marine Forces Pacific (MARFORPAC) is located in Hawaii. Its major units are the I MEF, headquartered at Camp Pendleton, California, and the III MEF, headquartered in Okinawa, Japan. I MEF in California has three MSCs: 1st MarDiv and 1st MLG, located at Camp Pendleton, and 3d MAW, based at MCAS, Miramar. III MEF includes forward-deployed forces from I MEF and II MEF and has 3d MarDiv, 3d MLG, and 1st MAW as its MSCs, all located in Okinawa. Some units of III MEF are based permanently in Hawaii at Marine Corps Base, Kanehoe Bay, Hawaii.

In addition, units of the Reserve division-wing team—and 4th MarDiv and 4th MAW, headquartered in New Orleans under the Commander, Marine Corps Forces Reserve (MARFORRES)—train alongside regular Marine units and maintain the same high standards of readiness as the active forces. This side-by-side training supports overall readiness, the team concept and the “Total Force” policy. They are supported by the 4th MLG of MARFORRES, headquartered in New Orleans, Louisiana.

The Marine Corps demonstrates its global perspective in more than 40 major exercises conducted annually around the globe. Operating literally in “every clime and place,” Marines take part in cold-weather training in Europe and Korea, as well as a variety of multinational exercises in other parts of the world.

The Marine Corps routinely conducts about 5 Integrated Training Exercises (ITXs) each year at the unique air-ground combat training center located at Twentynine Palms, California. In the open, unrestricted environment of the Mojave Desert, the readiness and combined arms capabilities of all elements of the Marine air-ground team and total force take part in exercises and receive evaluations. Each exercise includes live firing and is built around an infantry unit. Exercises are supported by fixed- and rotary-wing aircraft, artillery, light-armored reconnaissance vehicles, amphibious assault vehicles, engineers, and tanks. The exercises provide realistic training to prepare today’s Marines for tomorrow’s battlefields.


The Marine Corps exists in readiness for instant combat prepared for the battlefields of the future. Marines expect to be “first to fight.” The close relationship between Marine Corps forces and the U.S. Navy helps ensure that ready Marine forces will be on or near the scene when a crisis erupts.
Marine Corps forces fulfill a broad range of general purpose missions. Equally important during peacetime, they serve as essential elements of U.S. deterrence. They project U.S. influence abroad by assisting diplomatic efforts, providing humanitarian relief and protecting U.S. nationals, embassy personnel, and American interests abroad. In times of impending crisis, they provide a stabilizing influence or an on-the-scene initial response with a balanced combat capability within the MAGTF framework. They are capable of being rapidly deployed and rapidly reinforced, and they arrive combat-equipped and fully ready for action.

By any standards, Marine training has always been—and will remain—tough, realistic and extremely demanding. Marines ‘Train as they fight and fight as they are trained’ in order to survive in combat. Among the Corps’ unchanging priorities is the team concept—Marines train and fight as a team. The fully integrated air-ground team stands at the core of the Marine battle ethic, bringing all of the weapons and firepower available to the combat Marine, in a well-coordinated combined arms array.

The overall mission of the Marine Corps has been defined by tradition and statute. Its organization and functions are keyed to its enduring task as a force-in-readiness. Since 1775, Marines have served “to advantage by sea when required.” In pressing that “advantage by sea”—and land and air—Marines have founded proud traditions and established an enviable history.