National Command Authority (NCA) is a term that was used by the Department of Defense of the United States to refer to the ultimate source of lawful military orders.
The NCA was first alluded to in a 1960 Department of Defense document. It included at least the president of the United States as commander-in-chief and the secretary of defense. The term has no statutory or constitutional basis and was replaced in 2002 in favor of explicitly referring to the president and/or the secretary of defense.
The term also refers to communications with the commanding officers of the Unified Combatant Commands to put U.S. forces into action.
Authorization of a nuclear or strategic attack
Only the president can direct the use of nuclear weapons by U.S. Armed Forces, through plans like OPLAN 8010-12. The president has unilateral authority as commander-in-chief to order that nuclear weapons be used for any reason at any time.