Mission

The Marine Corps serves as a versatile combat element, and is adapted to a wide variety of combat operations. The Marine Corps was initially composed of infantry combat forces serving aboard naval vessels, responsible for security of the ship, its captain and officers, offensive and defensive combat during boarding actions, by acting as sharpshooters, and carrying out amphibious assaults. The Marines fully developed and used the tactics of amphibious assault in World War II, most notably in the Pacific Island Campaign.

Since its creation in 1775 the Corps' role has expanded significantly. The Marines have a unique mission statement, and, alone among the branches of the U.S. armed forces, "shall, at any time, be liable to do duty in the forts and garrisons of the United States, on the seacoast, or any other duty on shore, as the President, at his discretion, shall direct." In this special capacity, charged with carrying out duties given to them directly by the President of the United States, the Marine Corps serves as an all-purpose, fast-response task force, capable of quick action in areas requiring emergency intervention.

The Marine Corps possesses organic ground and air combat elements, and relies upon the US Navy to provide sea combat elements to fulfill its mission as "America's 9-1-1 Force." Ground combat elements are largely contained in three Marine divisions, or "MarDivs." The 1st Marine Division is based out of Camp Pendleton, California, the 2nd out of Camp LeJeune, North Carolina, while the third is based on Okinawa, Japan. Recon battalions are composed of the elite Marines, and their mission is to scout the enemy or even to penetrate the enemy line.

Air combat elements are similarly grouped in the first, second and third Marine wings.

Marine tactics and doctrine tends to emphasize aggressiveness and the offensive, compared to Army tactics for similar units. The Marines have been central in developing groundbreaking tactics for maneuver warfare; they can be credited with the development of helicopter insertion doctrine and modern amphibious assault.

The Marines also maintain an operational and training culture dedicated to emphasizing the infantry combat abilities of every Marine. All Marines receive training first and foremost as riflemen, and thus the Marine Corps at heart functions as an infantry corps. The Marine Corps is famous for the saying "Every Marine is a rifleman."

While the Marine Corps does not necessarily fill unique combat roles, only when combined do the US Army, Navy, and US Air Force overlap every area that the Marine Corps covers. As a force, the Marines consistently use all essential elements of combat (air, ground, sea) together. While the creation of joint commands under the Goldwater-Nichols Act has improved interservice coordination between the larger services, the Marine Corps' ability to permanently maintain integrated multi-element task forces under a single command provides a special ability to respond to flexibility and urgency requirements.

The Marines argue that they do not and should not take the place of the other services, any more than an ambulance takes the place of a hospital. Nonetheless, when a pressing emergency develops, the Marines essentially act as a stopgap, to get into and hold an area until the larger machinery can be mobilized. The opinions of other military men and politicians have, at times, differed, and President Harry S. Truman considered abolishing the Corps as part of the 1948 reorganization of the military. As Harry Truman said, "The only propaganda machine that rivals that of Stalin is that of the United States Marine Corps." Truman felt that the Marines were useless, despite their many successes in World War Two and Korea. The United States Marine Corps is mainly used as an immediate resource of troops that can be deployed immediately to any part of the world. The Marines do not win wars by themselves. Their mission is to hold an area until the heavy reinforcements (i.e. the Army) arrive. Note that in the Second Iraq War Marines were deployed first while Army units organized themselves.

An example of this coordinated, time-sensitive capability could be seen in 1990, when the 22nd Marine Expeditionary Unit (22nd MEU) conducted Operation Sharp Edge, a noncombatant evacuation operation, or NEO, in the west African city of Monrovia, Liberia. Liberia suffered from civil war at the time, and civilian citizens of the United States and other countries could not leave via conventional means. Sharp Edge ended in success. Only one reconnaissance team came under fire, with no casualties incurred on either side, and the Marines evacuated several hundred civilians within hours to U.S. Navy vessels waiting offshore.