3-21. State and federal Army leaders apply doctrinal principles that will ensure all Army forces achieve unity of effort when state military and federal military units are partners in a response. Army units supporting civil authorities are likely to serve alongside military partners under different chains of command. The particular duty status of a unit (the legal standing of the organization) determines its chain of command and in some cases the missions it may undertake in the homeland. Depending on their status, units may be described as federal forces or state forces. However, the inclusion of National Guard units within either category varies.