((a)) The President may vacate the promotion to the grade of brigadier general or rear admiral (lower half) of an officer who has served less than 18 months in that grade after promotion to that grade under this chapter.
((b)) An officer of the Army, Air Force, or Marine Corps whose promotion is vacated under this section holds the regular grade of colonel, if he is a regular officer, or the reserve grade of colonel, if he is a reserve officer. An officer of the Navy whose promotion is vacated under this section holds the regular grade of captain, if he is a regular officer, or the reserve grade of captain, if he is a reserve officer.
((c)) The position on the active-duty list of an officer whose promotion is vacated under this section is the position he would have held had he not been promoted to the grade of brigadier general or rear admiral (lower half).