Why ARES is an ARRL-sponsored field organization: any licensed amateur who registers their skills and equipment with the local Emergency Coordinator can serve, and no other membership or government tie is required. It is a volunteer public service group, not a licensing class or a certification program. Its counterpart, RACES, is the civil-defense service activated by government emergency management authorities under FCC rules.
Watch out The military message-handling description fits MARS (Military Auxiliary Radio System), and the RACES certification choice confuses ARES with the separate government-activated civil emergency service.
ARES = Amateurs Registering Equipment and Skills. ARRL volunteers, not military, not a class.