10 U.S.C. § 136

(a) There is an Under Secretary of Defense for Personnel and Readiness, appointed from civilian life by the President, by and with the advice and consent of the Senate. A person may not be appointed as Under Secretary within seven years after relief from active duty as a commissioned officer of a regular component of an armed force. (b) Subject to the authority, direction, and control of the Secretary of Defense, the Under Secretary of Defense for Personnel and Readiness shall perform such duties and exercise such powers as the Secretary of Defense may prescribe in the areas of military readiness, total force management, military and civilian personnel requirements, military and civilian personnel training, military and civilian family matters, exchange, commissary, and nonappropriated fund activities, personnel requirements for weapons support, National Guard and reserve components, and health affairs. (c) The Under Secretary of Defense for Personnel and Readiness takes precedence in the Department of Defense after the Under Secretary of Defense (Comptroller). (d) The Under Secretary of Defense for Personnel and Readiness is responsible, subject to the authority, direction, and control of the Secretary of Defense, for the monitoring of the operations tempo and personnel tempo of the armed forces. The Under Secretary shall establish, to the extent practicable, uniform standards within the Department of Defense for terminology and policies relating to deployment of units and personnel away from their assigned duty stations (including the length of time units or personnel may be away for such a deployment) and shall establish uniform reporting systems for tracking deployments.