US Marine Corps Mission: The United States Marine Corps serves as an amphibious force-in-readiness. As outlined in 10 U.S.C. § 5063 and as originally introduced under the National Security Act of 1947, it has three primary areas of responsibility:

• The seizure or defense of advanced naval bases and other land operations to support naval campaigns;
• The development of tactics, technique, and equipment used by amphibious landing forces; and
• Such other duties as the President may direct.

This last clause, while seemingly redundant given the president's position as Commander-in-chief, is a codification of the expeditionary duties of the Marine Corps. It derives from similar language in the Congressional acts "For the Better Organization of the Marine Corps" of 1834, and "Establishing and Organizing a Marine Corps" of 1798. In 1951, the House of Representatives' Armed Services Committee called the clause "one of the most important statutory — and traditional — functions of the Marine Corps." It noted that the corps has more often than not performed actions of a non-naval nature, including its famous actions in the War of 1812, at Tripoli, Chapultepec, numerous counter-insurgency and occupational duties (such as those in Central America), World War I, and the Korean War. While these actions are not accurately described as support of naval campaigns nor as amphibious warfare, their common thread is that they are of an expeditionary nature, using the mobility of the Navy to provide timely intervention in foreign affairs on behalf of American interests.

In addition to its primary duties, the Marine Corps has missions in direct support of the White House and the State Department. The Marine Band, dubbed the "President's Own" by Thomas Jefferson, provides music for state functions at the White House. Marines guard presidential retreats, including Camp David, and the Marines of the Executive Flight Detachment of HMX-1 provide helicopter transport to the President and Vice President, using the call signs "Marine One" and "Marine Two" respectively.

By authority of the 1946 Foreign Service Act, the Marine security guards of the Marine Embassy Security Command provide security for American embassies, legations, and consulates at more than 140 posts worldwide.