United States Marine Corps (USMC) is a branch of the United States armed forces.
While concerned almost exclusively with shipboard security service and amphibious warfare in its formative years, the Marine Corps has evolved to fill a unique, multi-purpose role within the modern United States military. It 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 (e.g. the U.S. Army) arrive. In Operation Iraqi Freedom Marines were deployed first while Army units organized themselves.
Both the Marine Corps and the United States Navy fall under the umbrella of the Department of the Navy. While organizationally separate forces, the two services work closely together.
The Marine Corps is the second smallest of the five branches of the United States armed forces. Only the United States Coast Guard, part of the Department of Homeland Security, is smaller.
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.
Since its creation in 1775 the Corps' role has expanded significantly. The Marines fully developed and used the tactics of amphibious assault in World War II, most notably in the Pacific Island Campaign. 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 inter-service 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.