USMC- Mission of the Marine Corps

The Marine Corps shall: Be organized, trained and equipped to provide Fleet Marine Forces for service with the U.S. Fleet in the seizure or defense of advanced Naval bases, and for the conduct of such land operations essential to the prosecution of a naval campaign.
Provide detachments for service on armed vessels of the U.S. Navy, and security detachments for the protection of property at Naval stations and bases.
In connection with the Army, Navy, and Air Forces, develop the tactical techniques and equipment employed by landing forces in amphibious operations.
Train and equip Marine forces for airborne operations in coordination with the Army, Navy and Air Forces..
Maintain four fully equipped and manned Divisions/Wings. Marine Regular forces shall comprise three of these Divisions/Wings. The fourth shall be the Marine Reserve.