In designating a competitive category of officers pursuant to section 649a of this title, the Secretary of a military department shall specify the number of opportunities for consideration for promotion to be afforded officers of the armed force concerned within the category for promotion to each grade above the grade of first lieutenant or lieutenant (junior grade), as applicable.

The Secretary of a military department may modify the number of opportunities for consideration for promotion to be afforded officers of an armed force within a competitive category for promotion to a particular grade, as previously specified by the Secretary pursuant subsection (a) or this subsection, not more frequently than once every five years.

The Secretary of Defense may modify the number of opportunities for consideration for promotion to be afforded officers of an armed force within a competitive category for promotion to a particular grade, as previously specified or modified pursuant to any provision of this section, at the discretion of the Secretary.

The number of opportunities for consideration for promotion to be afforded officers of an armed force within a competitive category for promotion to a particular grade, as specified or modified pursuant to any provision of this section, may not exceed five opportunities.

If, by reason of a reduction in the number of opportunities for consideration for promotion under this section, an officer would no longer have one or more opportunities for consideration for promotion that were available to the officer before the reduction, the officer shall be afforded one additional opportunity for consideration for promotion after the reduction.