• Provide Fleet Marine Forces of combined arms, together with supporting air components, for service with the United States Fleet in the seizure or defense of advanced naval bases and for the conduct of such land operations as may be essential to the prosecution of a naval campaign.
  
  
• Provide detachments and organizations for service on armed vessels of the Navy, and security detachments for the protection of naval property at naval stations and bases.
  
  
• Develop, in coordination with the Army, Navy, and Air Force, the doctrines, tactics, techniques, and equipment employed by landing forces in amphibious operations. The Marine Corps shall have primary interest in the development of those landing force doctrines, tactics, techniques, and equipment which are of common interest to the Army and the Marine Corps.
  
  
• Provide, as required, Marine forces for airborne operations, in coordination with the Army, the Navy, and the Air Force and in accordance with doctrines established by the Joint Chief of Staff.
  
  
• Develop, in coordination with the Army, the Navy, and the Air Force, doctrines, procedures, and equipment of interest to the Marine Corps for airborne operations which are not provided for by the Army.
  
  
• Be prepared, in accordance with integrated joint mobilization plans, for the expansion of the peacetime components to meet the needs of war.
  
  
• Perform such other duties as the President may direct.
  
  

The collateral functions of the Marine Corps are to:

• Maintain a Marine Corps Reserve for the purpose of providing trained units and qualified individuals to be available for active duty in the Marine Corps in time of war or national emergency and at such other times as the national security may require.
  
  
• Provide Marine officer and enlisted personnel in support of the Department of State security program overseas.
  
  

The implied functions of the Marine Corps are to:

• Organize, train, and equip Marine Corps forces for assignment to unified and specified commands in support of national war plans.
  
  
• Assign such forces to unified and specified commands, as directed.
  
  
• Support Marine Corps and other forces assigned to unified and specified commands, as directed.
  
  
• Be prepared, in accordance with integrated joint mobilization plans, to expand peacetime components to meet the needs of war.
  
  
• Marine Corps aviation shall be organized to provide supporting air components for the Fleet Marine Forces in the seizure or defense of advanced naval bases and in the conduct of such land operations as may be essential to the prosecution of a naval campaign; and, as a collateral function, to participate as an integral component of naval aviation in the execution of such other Navy functions as the fleet commanders may direct.
  
  

Marine Corps Manual, Chapter 1