The President may appoint, by and with the advice and consent of the Senate, one Commandant for a period of four years, who may be reappointed for further periods of four years, who shall act as Chief of the Coast Guard. The term of an appointment, and any reappointment, shall begin on June 1 of the appropriate year and end on May 31 of the appropriate year, except that, in the event of death, retirement, resignation, or reassignment, or when the needs of the Service demand, the Secretary may alter the date on which a term begins or ends if the alteration does not result in the term exceeding a period of 4 years. The Commandant shall be appointed from the officers on the active duty promotion list serving above the grade of captain who have completed at least ten years of active service as a commissioned officer in the Coast Guard. The Commandant while so serving shall have the grade of admiral.