10 U.S.C. § 14003

(a) Position on List .— Officers shall be carried on the reserve active-status list of the armed force of which they are members in the order of seniority of the grade in which they are serving in an active status. Officers serving in the same grade shall be carried in the order of their rank in that grade. (b) Effect on Position Held by Reason of Temporary Appointment or Assignment .— An officer whose position on the reserve active-status list results from service under a temporary appointment or in a grade held by reason of assignment to a position has, when that appointment or assignment ends, the grade and position on that list that the officer would have held if the officer had not received that appointment or assignment.