(a) Notwithstanding section 635 or 636 of title 10, United States Code, as added by this Act, but subject to subsection (b), a regular officer of the Army or Air Force—“(1) who on the effective date of this Act [Sept. 15, 1981] is serving in or is on a list of officers recommended for promotion to the temporary grade of brigadier general or major general;
“(2) whose regular grade on such date is below such temporary grade; and
“(3) who is promoted pursuant to section 601(a) to the regular grade equivalent to such temporary grade,
shall be subject to mandatory retirement for years of service in accordance with the laws applicable on the day before the effective date of this Act to officers in the permanent grade he held on such date. However, such an officer shall not be subject to a mandatory retirement date which is earlier than the first day of the month following the month of the thirtieth day after he completes 30 years of service as computed under section 3927(a) or 8927(a), as appropriate, of title 10, United States Code, as in effect on the day before the effective date of this Act.
“(b)(1) The Secretary of the Army or the Secretary of the Air Force, as appropriate, may convene selection boards under this section for the purpose of recommending from among officers described in subsection (a) officers to be selected to be subject to mandatory retirement for years of service in accordance with the laws applicable on the day before the effective date of this Act [Sept. 15, 1981] to officers in the permanent grade to which such officers were promoted pursuant to section 601(a) or to officers in a lower permanent grade higher than the permanent grade held by such officers on the day before the effective date of this Act.
“(2) Upon the recommendation of a selection board convened under this section, the Secretary concerned may select officers described in subsection (a) to be subject to mandatory retirement in accordance with the provisions of section 3922, 3923, 8922, or 8923, as appropriate, of title 10, United States Code, as in effect on the day before the effective date of this Act [Sept. 15, 1981], rather than in the manner described in subsection (a).
“(3) Any selection board convened under this section shall be convened in accordance with the provisions of section 3297 or 8297, as appropriate, of title 10, United States Code, as in effect on the day before the effective date of this Act [Sept. 15, 1981].
“(c) This section does not apply to an officer who—“(1) is sooner retired or separated under another provision of law;
“(2) is promoted to the permanent grade of brigadier general pursuant to section 601(a) and is subsequently promoted to the permanent grade of major general under chapter 36 of title 10, United States Code, as added by this Act; or
“(3) is continued on active duty under section 637 of title 10, United States Code, as added by this Act.