(a) Assignment of Forces.—(1) As directed by the Secretary of Defense, the Secretaries of the military departments shall assign specified forces under their jurisdiction to unified and specified combatant commands or to the United States element of the North American Aerospace Defense Command to perform missions assigned to those commands. The Secretary of Defense shall ensure that such assignments are consistent with the force structure prescribed by the President for each combatant command.

(2) A force not assigned to a combatant command or to the United States element of the North American Aerospace Defense Command under paragraph (1) shall remain assigned to the military department concerned for carrying out the responsibilities of the Secretary of the military department concerned as specified in section 7013, 8013, or 9013 of this title, as applicable.

(3) A force assigned to a combatant command or to the United States element of the North American Aerospace Defense Command under this section may be transferred from the command to which it is assigned only—

(A) by authority of the Secretary of Defense; and

(B) under procedures prescribed by the Secretary and approved by the President.

(4) Except as otherwise directed by the Secretary of Defense, all forces assigned to a unified combatant command shall be under the command of the commander of that command. The preceding sentence applies to forces assigned to a specified combatant command only as prescribed by the Secretary of Defense.

(b) Chain of Command.—Unless otherwise directed by the President, the chain of command to a unified or specified combatant command runs—

(1) from the President to the Secretary of Defense; and

(2) from the Secretary of Defense to the commander of the combatant command.