((a)) Each officer of the Regular Coast Guard appointed under who is serving in the grade of lieutenant (junior grade) or lieutenant and who has failed of selection for promotion to the grade of lieutenant or lieutenant commander, respectively, for the second time shall:
((1)) be honorably discharged on June 30 of the promotion year in which his second failure of selection occurs; or
((2)) if he so requests, be honorably discharged at an earlier date without loss of benefits that would accrue if he were discharged on that date under clause (1); or
((3)) if on the date specified for his discharge in this section he is eligible for retirement under any law, be retired under that law on that date.
((b)) Each officer subject to discharge or retirement under subsection (a) may elect to revert to his permanent grade.