((a)) ** .—** The Secretary of the military department concerned may authorize an officer in a grade above grade O–2 to remain on active duty after the date otherwise provided for the separation or retirement of the officer in section 632, 633, 634, 635, or 636 of this title, as applicable, if the officer has a military occupational specialty, rating, or specialty code in a military specialty designated pursuant to subsection (b).
((b)) ** .—** Each Secretary of a military department shall designate the military specialties in which a military occupational specialty, rating, or specialty code, as applicable, assigned to members of the armed forces under the jurisdiction of such Secretary authorizes the members to be eligible for continuation on active duty as provided in subsection (a).
((c)) ** .—** An officer continued on active duty pursuant to this section shall, if not earlier retired, be retired on the first day of the month after the month in which the officer completes 40 years of active service.
((d)) ** .—** The Secretaries of the military departments shall carry out this section in accordance with regulations prescribed by the Secretary of Defense. The regulations shall specify the criteria to be used by the Secretaries of the military departments in designating military specialties for purposes of subsection (b).