All officers of the National Guard shall be appointed and commissioned by the Governor, through the Adjutant General.
Within the organization, insofar as practicable, all appointments and promotions shall be based on professional qualifications, efficiency, length of service in grade, length of commissioned service, and demonstrated command and staff ability at the appropriate level, and will be effected only when an appropriate vacancy exists in the applicable table of organization and equipment or table of organization or distribution.
Va. Code § 44-27