10 U.S.C. § 138

(a) (1) There are 20 Assistant Secretaries of Defense. (2) The Assistant Secretaries of Defense shall be appointed from civilian life by the President, by and with the advice and consent of the Senate. (b) (1) The Assistant Secretaries shall perform such duties and exercise such powers as the Secretary of Defense may prescribe. (2) (A) One of the Assistant Secretaries is the Assistant Secretary of Defense for Special Operations and Low Intensity Conflict. The principal duty of the Assistant Secretary shall be the overall supervision (including oversight of policy and resources) of special operations activities (as defined in section 167(k) of this title ) and low intensity conflict activities of the Department of Defense. The Assistant Secretary is the principal civilian adviser to the Secretary of Defense on special operations and low intensity conflict matters and (after the Secretary and Deputy Secretary) is the principal special operations and low intensity conflict official within the senior management of the Department of Defense. A person may not be appointed as Assistant Secretary within seven years after relief from active duty as a commissioned officer of a regular component of an armed force. Subject to the authority, direction, and control of the Secretary of Defense, the Assistant Secretary shall do the following: (i) Exercise authority, direction, and control of all special-operations peculiar administrative matters relating to the organization, training, and equipping of special operations forces through the administrative chain of command specified in section 167(f) of this title . (ii) Assist the Secretary and the Under Secretary of Defense for Policy in the development and supervision of policy, program planning and execution, and allocation and use of resources for the activities of the Department of Defense for the following: (I) Irregular warfare, combating terrorism, and the special operations activities specified by section 167(k) of this title . (II) Integrating the functional activities of the headquarters of the Department to most efficiently and effectively provide for required special operations forces and capabilities. (B) In the discharge of the responsibilities specified in subparagraph (A)(i), the Assistant Secretary is immediately subordinate to the Secretary of Defense. Unless otherwise directed by the President, no officer below the Secretary may intervene to exercise authority, direction, or control over the Assistant Secretary in the discharge of such responsibilities. (3) One of the Assistant Secretaries is the Assistant Secretary of Defense for Legislative Affairs. The principal duty of the Assistant Secretary shall be the overall supervision of legislative affairs of the Department of Defense. (4) One of the Assistant Secretaries is the Assistant Secretary of Defense for Nuclear Deterrence, Chemical, and Biological Defense Policy and Programs. The Assistant Secretary is the principal civilian adviser to the Secretary of Defense on nuclear deterrence policies, operations, and associated programs within the senior management of the Department of Defense. The principal duty of the Assistant Secretary shall be the overall supervision of nuclear deterrence policy, resources, and activities of the Department of Defense. (A) Subject to the authority, direction, and control of the Secretary of Defense, the Assistant Secretary shall— (i) advise and assist the Secretary of Defense, the Deputy Secretary of Defense, the Under Secretary of Defense for Acquisition and Sustainment, and the Under Secretary of Defense for Policy in the development and supervision of policy, program planning and execution, and allocation and use of resources for the activities of the Department of Defense on all matters relating to the sustainment, operation, and modernization of United States nuclear forces as defined in section 499c(d) of this title ; (ii) communicate views on issues within the responsibility of the Assistant Secretary directly to the Secretary of Defense and the Deputy Secretary of Defense without obtaining the approval or concurrence of any other official within the Department of Defense; (iii) serve as the Staff Director of the Nuclear Weapons Council established by section 179 of this title ; (iv) serve as the principal Department of Defense civilian responsible for oversight of portfolio management for nuclear forces established by section 499c of this title ; (v) serve as the principal interface with the Department of Energy on issues relating to nuclear fuels; (vi) in coordination with the Assistant Secretary of Defense for Energy, Installations, and Environment, advise the Secretary of Defense on nuclear energy matters; and (vii) advise and assist the Secretary of Defense, the Deputy Secretary of Defense, the Under Secretary of Defense for Acquisition and Sustainment, and the Under Secretary of Defense for Policy on all matters relating to the defense against chemical, biological, and other weapons of mass destruction. (B) Unless otherwise directed by the President or statute, no officer other than the Secretary of Defense, Deputy Secretary of Defense, the Under Secretary of Defense for Acquisition and Sustainment, and the Under Secretary of Defense for Policy may intervene to exercise authority, direction, or control over the Assistant Secretary in the discharge of responsibilities specified in subparagraph (A). (5) One of the Assistant Secretaries is the Assistant Secretary of Defense for Space Policy. The principal duty of the Assistant Secretary shall be the overall supervision of policy of the Department of Defense for space warfighting. (6) One of the Assistant Secretaries is the Assistant Secretary of Defense for Industrial Base Policy. The Assistant Secretary shall advise the Under Secretary of Defense for Acquisition and Sustainment on industrial base policies. (7) One of the Assistant Secretaries is the Assistant Secretary of Defense for International Armaments Cooperation, who shall report directly to the Under Secretary of Defense for Acquisition and Sustainment. The principal duty of the Assistant Secretary shall be to carry out section 133b(b)(10) of this title . (8) One of the Assistant Secretaries is the Assistant Secretary of Defense for Energy, Installations, and Environment. The principal duty of the Assistant Secretary shall be the overall supervision of matters relating to energy, installations, and the environment for the Department of Defense. (9) One of the Assistant Secretaries is the Assistant Secretary of Defense for Cyber Policy. The principal duty of the Assistant Secretary shall be the overall supervision of policy of the Department of Defense for cyber. The Assistant Secretary is the Principal Cyber Advisor described in section 392a(a) of this title . (c) Except as otherwise specifically provided by law, an Assistant Secretary may not issue an order to a military department unless— (1) the Secretary of Defense has specifically delegated that authority to the Assistant Secretary in writing; and (2) the order is issued through the Secretary of the military department concerned. (d) The Assistant Secretaries take precedence in the Department of Defense after the Secretary of Defense, the Deputy Secretary of Defense, the Secretaries of the military departments, the Under Secretaries of Defense, the officials serving in positions specified in section 131(b)(4) of this title , and the Deputy Under Secretaries of Defense. The Assistant Secretaries take precedence among themselves in the order prescribed by the Secretary of Defense. (e) The number of Deputy Assistant Secretaries of Defense may not exceed 62.