((a)) The Secretary concerned shall maintain for each armed force under the jurisdiction of that Secretary a single list of all warrant officers (other than warrant officers described in ) who are on active duty.

((b)) The Secretary concerned may establish competitive categories for promotion. Warrant officers in the same competitive category shall compete among themselves for promotion.

((c)) Before convening a selection board under , the Secretary concerned shall determine for each grade (or grade and competitive category) to be considered by the board the following:

((1)) The maximum number of warrant officers to be recommended for promotion.

((2)) A promotion zone for warrant officers on the warrant officer active-duty list.

((d)) The position of a warrant officer on the warrant officer active-duty list shall be determined as follows:

((1)) Warrant officers shall be carried in the order of seniority of the grade in which they are serving on active duty.

((2)) Warrant officers serving in the same grade shall be carried in the order of their rank in that grade.

((3)) A warrant officer on the warrant officer active-duty list who receives a temporary appointment or a temporary assignment in a grade other than a warrant officer grade or chief warrant officer grade shall retain his position on the warrant officer active-duty list while so serving.

((e)) A chief warrant officer may not be considered for promotion to the next higher grade under this chapter until the officer has completed two years of service on active duty in the grade in which the officer is serving.