10 U.S.C. § 111

(a) The Department of Defense is an executive department of the United States. (b) The Department is composed of the following: (1) The Office of the Secretary of Defense. (2) The Joint Chiefs of Staff. (3) The Joint Staff. (4) The Defense Agencies. (5) Department of Defense Field Activities. (6) The Department of the Army. (7) The Department of the Navy. (8) The Department of the Air Force. (9) The unified and specified combatant commands. (10) Such other offices, agencies, activities, and commands as may be established or designated by law or by the President. (11) All offices, agencies, activities, and commands under the control or supervision of any element named in paragraphs (1) through (10). (c) If the President establishes or designates an office, agency, activity, or command in the Department of Defense of a kind other than those described in paragraphs (1) through (9) of subsection (b), the President shall notify Congress not later than 60 days thereafter.