The commission of an officer shall be vacated by death, by acceptance by proper authority of resignation, by discharge on account of inefficiency, for physical disqualifications, when dropped from the rolls for an absence without leave for three months, by discharge to accept a commission in the United States Army, United States Air Force, United States Navy, or a reserve component thereof, when transferred to the United States Army Reserve upon the expiration of six months as a member of the Inactive National Guard, upon a finding by the Adjutant General that the officer is a security risk as a result of subversive activity, for personal traits of character, or by dismissal pursuant to sentence of a general court-martial.