Tenn. Code Ann. § 58-1-410

During such time as the state guard is not activated, the adjutant general is authorized and empowered, on the approval of the governor, to set up and maintain a reserve organization of the state guard upon a voluntary basis under such system as to the adjutant general may seem most feasible in order to provide means for the creation of an armed force in case the national guard of the state be again called into federal service.