(a) Special courts-martial may be convened by--

(1) any person who may convene a general court-martial;

(2) the commanding officer of a force of the organized militia, or of a garrison, fort, camp, station, air base or other place where members of a force of the organized militia are on duty;

(3) the commanding officer of a division, brigade, detached or separate battalion, or corresponding unit of the army national guard, the New York guard or of any other land force of the organized militia;

(4) the commanding officer of a wing, group, detached or separate squadron or corresponding unit of the air national guard;

(5) the commanding officer of any naval vessel, and the commanding officer of any area, brigade, battalion, division, marine battalion or separate marine company of the naval militia;

(6) the commanding officer of any separate or detached command or group of detached units of any of the forces of the organized militia placed under a single commander; or

(7) the commanding officer or officer in charge of any other command when empowered by the adjutant general.

(b) When any such officer is an accuser, the court shall be convened by superior competent authority, and may in any case be convened by such authority when deemed advisable by him.