S.C. Code Ann. § 25-1-2610

(1) Any officer off or on duty with the military forces is eligible to serve as a member on all courts-martial for the trial of any person who may lawfully be brought before such courts for trial. (2) Any enlisted member of the military forces who is not a member of the same unit as the accused is eligible to serve on general and special courts-martial for the trial of any enlisted member of the military forces who may lawfully be brought before such courts for trial, but he may 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 a request, the accused may not be tried by a general or special 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 members cannot be obtained on account of physical conditions or military exigencies. If such members may not be obtained, the court may be assembled and the trial held without them, but the convening authority shall make a detailed written statement, to be appended to the record, stating why they could not be obtained. In this subsection, the word "unit" means any regularly organized body of the military forces not larger than a company, a squadron, or a body corresponding to one of them. (3) When it can be avoided, no person subject to the Code of Military Justice may be tried by a court-martial composed of any members who are junior to him in rank or grade. (4) When convening a court-martial, the convening authority shall detail as members such members of the military force 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 general or special court-martial when he is the accuser or a witness for the prosecution or has acted as investigation officer or as counsel in the same case.