10 U.S.C. § 611

(a) Whenever the needs of the service require, the Secretary of the military department concerned shall convene selection boards to recommend for promotion to the next higher permanent grade, under subchapter II of this chapter, officers on the active-duty list in each permanent grade from first lieutenant through brigadier general in the Army, Air Force, Marine Corps, or Space Force and from lieutenant (junior grade) through rear admiral (lower half) in the Navy. The preceding sentence does not require the convening of a selection board in the case of officers in the permanent grade of first lieutenant or, in the case of the Navy, lieutenant (junior grade) when the Secretary concerned recommends for promotion to the next higher grade under section 624(a)(3) of this title all such officers whom the Secretary finds to be fully qualified for promotion. (b) Whenever the needs of the service require, the Secretary of the military department concerned may convene selection boards to recommend officers for continuation on active duty under section 637 of this title or for early retirement under section 638 of this title . (c) The convening of selection boards under subsections (a) and (b) shall be under regulations prescribed by the Secretary of Defense.