McRae's battalion was not part of the Arkansas State Troops organization. It was mustered directly into Confederate service as the 3rd Battalion Arkansas Volunteers on July 15, 1861, and as such was assigned to McCulloch's Confederate brigade. It was reorganized as a regiment and redesignated as the 21st Regiment Arkansas Infantry (not to be confused with the "other" 21st Arkansas Infantry) on December 3, 1861. It was redesignated as the 15th Arkansas Infantry in October 1862, and, to avoid confusion with Josey's 15th Arkansas Regiment, was redesignated as the 15th (Northwest) Arkansas Infantry in February 1863.