10 U.S.C. § 7034

(a) There is a Vice Chief of Staff of the Army, appointed by the President, by and with the advice and consent of the Senate, from the general officers of the Army. (b) The Vice Chief of Staff of the Army, while so serving, has the grade of general without vacating his permanent grade. (c) The Vice Chief of Staff has such authority and duties with respect to the Department of the Army as the Chief of Staff, with the approval of the Secretary of the Army, may delegate to or prescribe for him. Orders issued by the Vice Chief of Staff in performing such duties have the same effect as those issued by the Chief of Staff. (d) When there is a vacancy in the office of Chief of Staff or during the absence or disability of the Chief of Staff— (1) the Vice Chief of Staff shall perform the duties of the Chief of Staff until a successor is appointed or the absence or disability ceases; or (2) if there is a vacancy in the office of the Vice Chief of Staff or the Vice Chief of Staff is absent or disabled, unless the President directs otherwise, the most senior officer of the Army in the Army Staff who is not absent or disabled and who is not restricted in performance of duty shall perform the duties of the Chief of Staff until a successor to the Chief of Staff or the Vice Chief of Staff is appointed or until the absence or disability of the Chief of Staff or Vice Chief of Staff ceases, whichever occurs first.