(1) Any commissioned officer is eligible to serve on any court-martial for the trial of any person who may lawfully be brought before such court for trial.

(2) Any warrant officer is eligible to serve on a court-martial for the trial of any person, other than a commissioned officer, who may lawfully be brought before such court for trial.

(3)(a) Any enlisted member, who is not a member of the same unit as the accused, is eligible to serve on a court-martial for the trial of any enlisted member of an armed force who may lawfully be brought before such court for trial, but he shall serve as a member of a court only if, before the conclusion of a session called by the military judge prior to trial or, in the absence of such a session, before the court is assembled for the trial of the accused, the accused personally has requested in writing that enlisted members serve on it. After such request, the accused may not be tried by a court-martial the membership of which does not include enlisted members in a number comprising at least one-third of the total membership of the court, unless eligible enlisted members cannot be obtained on account of physical conditions or military exigencies. If such members cannot be obtained, the court may be assembled and the trial held without them, but the assembling authority shall make a detailed written statement, to be appended to the record, stating why they could not be obtained.

(b) In this section, the word unit means any regularly organized body as defined by the Governor, but in no case may it be a body larger than a company, squadron, or body corresponding to one of them.

(4)(a) When it can be avoided, no member of the military forces may be tried by a court-martial any member of which is junior to him in rank or grade.

(b) When convening a court-martial, the convening authority shall detail as members thereof such members of the military forces as, in his opinion, are best qualified for the duty by reason of age, education, training, experience, length of service, and judicial temperament. No member of the military forces is eligible to serve as a member of a court-martial when he is the accuser or a witness for the prosecution or has acted as investigating officer or as counsel in the same case.