10 U.S.C. § 8456

(a) If the annual quota of midshipmen from— (1) enlisted members of the Regular Navy and the Regular Marine Corps; (2) enlisted members of the Navy Reserve and the Marine Corps Reserve; or (3) at large by the President; is not filled, the Secretary may fill the vacancies by nominating for appointment other candidates from any of these sources who were found best qualified on examination for admission and not otherwise nominated. (b) If it is determined that, upon the admission of a new class to the Academy, the number of midshipmen at the Academy will be below the authorized number, the Secretary may fill the vacancies by nominating additional midshipmen from qualified candidates designated as alternates and from other qualified candidates who competed for nomination and are recommended and found qualified by the Academic Board. At least three-fourths of those nominated under this subsection shall be from qualified alternates under paragraphs (2) through (8) of section 8454(a) of this title, and the remainder shall be from qualified candidates who competed for appointment under any other provision of law. An appointment of a nominee under this subsection is an additional appointment and is not in place of an appointment otherwise authorized by law. (c) The failure of a member of a graduating class to complete the course with his class does not delay the appointment of his successor.