A first lieutenant on the reserve active-status list of the Army, Air Force, or Marine Corps or a lieutenant (junior grade) on the reserve active-status list of the Navy who has failed of selection for promotion to the next higher grade for the second time and whose name is not on a list of officers recommended for promotion to the next higher grade shall be separated in accordance with

Subsection (a) does not apply (1) in the case of an officer retained as provided by regulation of the Secretary of the military department concerned in order to meet planned mobilization needs for a period not in excess of 24 months beginning with the date on which the President approves the report of the selection board which resulted in the second failure, or (2) as provided in section 12646 or 12686 of this title.

For the purposes of this chapter, an officer of the Army, Air Force, or Marine Corps on a reserve active-status list who holds the grade of first lieutenant, and an officer of the Navy on a reserve active-status list who holds the grade of lieutenant (junior grade), shall be treated as having failed of selection for promotion if the Secretary of the military department concerned determines that the officer would be eligible for consideration for promotion to the next higher grade by a selection board convened under section 14101(a) of this title if such a board were convened but is not fully qualified for promotion when recommending for promotion under section 14308(b)(4) of this title all fully qualified officers of the officer’s armed force in such grade who would be eligible for such consideration.