10 U.S.C. § 713: State Department: assignment or detail as couriers and building inspectors

(a) Upon the request of the Secretary of State, the Secretary of a military department may assign or detail members of the armed forces under his jurisdiction for duty—(1) as inspectors of buildings owned or occupied abroad by the United States; (2) as inspectors or supervisors of buildings under construction or repair abroad by or for the United States; and (3) as couriers of the Department of State. (b) The Secretary concerned may assign or detail a member for duty under subsection (a) with or without reimbursement from the Department of State. However, a member so assigned or detailed may be paid the traveling expenses authorized for officers of the Foreign Service of the United States. These expenses shall be paid from appropriations of the Department of State.