10 U.S.C. § 7229: Command: commissioned officers of Army Medical Department

(a) Except as provided in subsection (b), a commissioned officer of the Army Medical Department is not entitled to exercise command because of his rank, except within the Army Medical Department. (b) An officer of the Medical Service Corps may exercise command of troops that are not part of the Army Medical Department whenever authorized by the Secretary of the Army. The Secretary of the Army may delegate such authority to appropriate commanders as the interest of the Army may require.