(a) General rule.--It shall be an affirmative defense in a trial by court-martial that, at the time of the commission of the acts constituting the offense, the accused, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of the acts. Mental disease or defect does not otherwise constitute a defense.

(b) Burden of proof.--The accused has the burden of proving the defense of lack of mental responsibility by clear and convincing evidence.

(c) Instructions or findings by military judge.--Whenever lack of mental responsibility of the accused with respect to an offense is properly at issue, the military judge shall:

(1) in a court-martial not composed of only a military judge, instruct the members of the court as to the defense of lack of mental responsibility under this section and charge them to find the accused guilty, not guilty or not guilty only by reason of lack of mental responsibility; or

(2) in a court-martial composed of only a military judge, find the accused guilty, not guilty or not guilty only by reason of lack of mental responsibility.

(d) Finding of not guilty.--Notwithstanding section 5717 (relating to number of votes required), the accused shall be found not guilty only by reason of lack of mental responsibility if:

(1) a majority of the members of the court-martial present at the time the vote is taken determines that the defense of lack of mental responsibility has been established; or

(2) in the case of a court-martial composed of only a military judge, the military judge or summary court-martial officer determines that the defense of lack of mental responsibility has been established.