UNIFIED COMBATANT COMMANDS :: "Operational control of the U.S. combat forces is assigned to the nation's Unified Combat Commands. The chain of command runs from the President to the Secretary of Defense to the Unified Commanders in Chief. Orders and other communications from the President or Secretary are transmitted through the Chairman of the Joint Chiefs of Staff. A Unified Combatant Command is composed of forces from two or more services, has a broad and continuing mission and is normally organized on a geographical basis. The number of unified combatant commands is not fixed by law or regulation and may vary from time to time."  (Defense Almanac).
 

U.S. European Command  U.S. Pacific Command  U.S. Joint Forces Command  U.S. Southern Command  U.S. Central Command  U.S. Space Command  U.S. Special Operations Command  U.S. Transportation Command  U.S. Strategic Command