S.C. Code § 25-1-590
Officers and enlisted men of the National Guard of South Carolina must be retired by order of the commander-in-chief with a promotion of one grade, effective the date of retirement or medical discharge at the request of an officer or enlisted man upon completion of twenty or more years of honorable service in the National Guard of South Carolina, the Armed Forces of the United States, and reserve components of these branches, except that the last ten years of that service must have been in the South Carolina National Guard, or in the National Guard of the United States, and provided that the individual concerned was a member of the South Carolina National Guard at the time he was ordered to active duty in the National Guard of the United States status. The years of service requirements shall not apply to members of the National Guard of South Carolina who are medically discharged prior to the completion of at least twenty years of qualifying military service, so long as the individual's discharge is characterized as honorable. A commissioned officer holding the grade of major general upon retirement must be retired in that grade; a warrant officer holding the grade of chief warrant officer upon retirement must be retired in that grade; and an enlisted man holding the highest authorized enlisted grade upon retirement must be retired in that grade.
Retired officers and retired enlisted men shall draw no pay or allowances except when placed on duty. They must be subject to temporary detail by the commander-in-chief, and while on this duty, shall receive the same pay and allowances as officers and enlisted men of the same rank on the active list. On all occasions of duty or ceremony, retired officers and enlisted men shall take rank below officers and enlisted men of the same grade on the active list.
S.C. Code § 25-1-590