These are not the same unit...sounds like your ancestor was one of the "galvanized" yankees who was a Confederate who while in prison, agreed to join and was sent west to be on the frontier to guard against Indians. Damon was asking about a state unit the 3rd Arkansas INfantry, not 3rd US volunteers. Many Confederates joined out of prison but with the promise they would not fight their families etc but go west and defend against the Indians.