If the office of Adjutant General is vacated because of the death, resignation or retirement of the Adjutant General prior to the normal expiration of his term of office, the Governor shall appoint an officer of the active South Carolina National Guard, who is of field grade rank or higher and who has a minimum of fifteen years' active commissioned service in the South Carolina National Guard, to fill out the unexpired term of the former incumbent. The appointee, upon being duly qualified, shall be subject to all the duties and liabilities incident to the office and receive the compensation provided by law for the Adjutant General during his term of service.