(a) Notwithstanding any other provision of this title, whenever the Secretary determines that it is necessary to reduce the number of Reserve officers in an active status in any grade to provide a steady flow of promotion, or that there is an excessive number of Reserve officers in an active status in any grade, the Secretary may appoint and convene a retention board to consider all of the Reserve officers in that grade in an active status who have 18 years or more of service for retirement, except those officers who—

(1) are on extended active duty;

(2) are on a list of selectees for promotion;

(3) will complete 30 years total commissioned service by June 30th following the date that the retention board is convened; or

(4) have reached age 59 by the date on which the retention board is convened.

The retention board shall select and recommend a specified number of the officers under consideration for retention in an active status.

(b) This board shall—

(1) to the extent practicable, consist of at least 50 per centum Reserve officers;

(2) consist only of officers who are senior in rank to any officers being considered by that board; and

(3) to the extent practicable, consist of officers who have not served on the last previous retention board which considered officers of the same grade.

(c) Subject to section 12646 of title 10, a Reserve officer who is not recommended for retention in an active status under this section shall be given an opportunity to transfer to the Retired Reserve, if qualified, but unless so transferred shall, in the discretion of the Secretary, be transferred to the inactive status list or discharged on June 30 next following the date on which the report of the retention board is approved.

(d) The provisions of section 2117 of this title shall, to the extent that they are not inconsistent with this subchapter, apply to boards convened under this section.