The President or the Secretary concerned may drop from the rolls of the armed force concerned any Reserve—
(1)
who has been absent without authority for at least three months;
(2)
who may be separated under section
12687 of this title by reason of a sentence to confinement adjudged by a court-martial; or
(3)
who is sentenced to confinement in a Federal or State penitentiary or correctional institution after having been found guilty of an offense by a court other than a court-martial or other military court, and whose sentence has become final.