(a) Retirement for Years of Service.—(1) Except as provided in subsection (b), an officer of the Navy or Marine Corps serving as a permanent professor at the Naval Academy in the grade of commander or lieutenant colonel who is not on a list of officers recommended for promotion to the grade of captain or colonel, as the case may be, shall, if not earlier retired, be retired on the first day of the month after the month in which the officer completes 28 years of active commissioned service.

(2) Except as provided in subsection (b), an officer of the Navy or Marine Corps serving as a permanent professor at the Naval Academy in the grade of captain or colonel who is not on a list of officers recommended for promotion to the grade of rear admiral (lower half) or brigadier general, as the case may be, shall, if not earlier retired, be retired on the first day of the month after the month in which the officer completes 30 years of active commissioned service.

(b) Continuation on Active Duty.—(1) An officer subject to retirement under subsection (a) may have his retirement deferred and be continued on active duty by the Secretary of the Navy.

(2) Subject to section 1252 of this title, the Secretary of the Navy shall determine the period of any continuation on active duty under this section.

(c) Eligibility for Promotion.—A permanent professor at the Naval Academy in the grade of commander or lieutenant colonel who is continued on active duty as a permanent professor under subsection (b) remains eligible for consideration for promotion to the grade of captain or colonel, as the case may be.

(d) Retired Grade and Retired Pay.—Each officer retired under this section—

(1) unless otherwise entitled to a higher grade, shall be retired in the grade determined under section 1370 of this title; and

(2) is entitled to retired pay computed under section 8333 of this title.