And: Lineage. Air Force Instruction 84-105, para 2.1.1, states, "The lineages of permanent organizations are continuous. Neither inactivation nor disbandment terminates their lineage or heraldry." Lineage entails tracing the organizational actions affecting the history of an organization. The official USAF statement of lineage forms the foundation of the organization's history and governs the organization's inheritance of emblem and honors. A basic policy of the Air Force is that each organization will have a unique lineage. This policy was in effect in the War Department when military aviation was under the Army and has been continued by the United States Air Force since its inception in 1947. No two organizations can have the same lineage, although at different times in their existence they may have possessed similar or even identical designations. A description of the lineage system may be found in Air Force Instruction 38-101 "Air Force Organization." The Air Force is composed of primary organizations called units and establishments. Units divide among three primary categories: squadrons (the numbered flight is considered a "small" squadron), miscellaneous (a category including such organizations as bands, infirmaries, hospitals, etc.), and headquarters. The headquarters organizations serve as headquarters for establishments. Establishments are Air Force organizations at group echelon or higher, having a headquarters organization as their primary component.