Units are designated and organized hierarchical structures where personnel are assigned. Units come in different forms, each fulfilling a specific need. Units belong to a parent Command, Branch, Program, or Affiliate depending on their structure, with some specialized units belonging to multiple parents. Units are assigned to geographical Area Commands when not deployed. Generally units follow a set chain-of-command with clearly defined leadership and accountability. Units are led by a Unit Leader who is assisted by a Second-In-Command.