10 U.S.C. § 14701a

(a) In General .— The Secretary of the military department concerned may authorize a reserve commissioned officer in a grade above O-2 to remain on the reserve active-status list after the date otherwise provided for the separation or retirement of the officer under section 14505, 14506, or 14507 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) Military Specialties .— The 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 the reserve active-status list as provided in subsection (a). (c) Duration of Continuation .— An officer continued on the reserve active-status list pursuant to this section shall, if not earlier retired, transferred to the Retired Reserve, or discharged, be separated in accordance with section 14513 or 14514 of this title, as applicable, on the first day of the month after the month in which the officer completes 40 years of commissioned service. (d) Regulations .— 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).