(a) An officer on the active duty promotion list becomes eligible for consideration for promotion to the next higher grade at the beginning of the promotion year in which he completes the following amount of service computed from his date of rank in the grade in which he is serving:

(1) two years in the grade of lieutenant (junior grade);

(2) three years in the grade of lieutenant;

(3) four years in the grade of lieutenant commander;

(4) four years in the grade of commander; and

(5) three years in the grade of captain.

(b) For the purpose of this section, service in a grade includes all qualifying service in that grade or a higher grade, under either a temporary or permanent appointment. However, service in a grade under a temporary service appointment under section 2125 of this title is considered as service only in the grade that the officer concerned would have held had he not been so appointed.

(c) No officer may become eligible for consideration for promotion until all officers of his grade senior to him are so eligible.

(d) Except when his name is on a list of selectees, each officer who becomes eligible for consideration for promotion to the next higher grade remains eligible so long as he—

(1) continues on active duty; and

(2) is not promoted to that grade.

(e) An officer whose involuntary retirement or separation is deferred under section 2156 of this title is not eligible for consideration for promotion to the next higher grade during the period of that deferment.

(f) The Secretary may waive subsection (a) to the extent necessary to allow officers described therein to have at least two opportunities for consideration for promotion to the next higher grade as officers below the promotion zone.