Joint Chiefs of Staff
The Joint Chiefs of Staff is comprised of "the Chairman, the Vice Chairman, the Chief of Staff of the Army, the Chief of Naval Operations, the Chief of Staff of the Air Force, and the Commandant of the Marine Corps." 
"The collective body of the JCS is headed by the Chairman (or the Vice Chairman in the Chairman's absence), who sets the agenda and presides over JCS meetings. Responsibilities as members of the Joint Chiefs of Staff take precedence over duties as the Chiefs of Military Services. The Chairman of the Joint Chiefs of Staff is the principal military adviser to the President, Secretary of Defense, and the National Security Council (NSC), however, all JCS members are by law military advisers, and they may respond to a request or voluntarily submit, through the Chairman, advice or opinions to the President, the Secretary of Defense, or NSC. The executive authority of the Joint Chiefs of Staff has changed." 
"In World War II, the U.S. Joint Chiefs of Staff acted as executive agents in dealing with theater and area commanders, but the original National Security Act of 1947/also (PL 235 - 61 Stat. 496; U.S.C. 402) saw the Joint Chiefs of Staff as planners and advisers, not as commanders of combatant commands. In spite of this, the 1948 Key West Agreement allowed members of the Joint Chiefs of Staff to serve as executive agents for unified commands, a responsibility that allowed the executive agent to originate direct communication with the combatant command. Congress abolished this authority in a 1953 amendment to the National Security Act. Today, the Joint Chiefs of Staff have no executive authority to command combatant forces. The issue of executive authority was clearly resolved by the Goldwater-Nichols DOD Reorganization Act of 1986: 'The Secretaries of the Military Departments shall assign all forces under their jurisdiction to unified and specified combatant commands to perform missions assigned to those commands...'; the chain of command 'runs from the President to the Secretary of Defense; and from the Secretary of Defense to the commander of the combatant command.'"