Persons hereafter commissioned as officers of the national guard shall be selected from the following classes:

(1)  Officers or enlisted persons of the national guard;

(2)  Officers, active or retired, reserve officers, and former officers of the United States army, air force, navy, marine corps, or coast guard, enlisted men and former enlisted persons of the United States army, air force, navy, marine corps, or coast guard who have received an honorable discharge therefrom;

(3)  Graduates of any of the United States military and naval academies;

(4)  Graduates of schools, colleges, universities, and officers’ training camps, where they have received military instruction under the supervision of an officer of the armed forces on active duty who certified their fitness for appointment as commissioned officers;

(5)  For the technical branches or staff corps and departments, such other civilians as may be specially qualified for duty therein; and

(6)  Or otherwise, as the above classes shall be changed or altered by the laws of the United States and the regulations issued thereunder.