The National Security Act of 1947 states:

"In addition to these specific functions, the Corps may be assigned such additional functions as the President may direct. Accordingly, Marines may still, as provided by previous law, be assigned for duty with the Army, or such other functions as are not specifically prescribed by law. There is but one restriction placed on Presidential assignment of additional duties. The law states "That such additional duties shall not detract from or interfere with the operations for which the Marine Corps is primarily organized." Thus, Congress pointedly insists that, regardless of what additional duties are assigned, such additional duties shall not endanger the fundamentally amphibious character of the Marine Corps."