This is a list of United States Air Force squadrons. It covers both the independent United States Air Force (USAF) and its period as a branch of the US Army culminating as the Army Air Forces up to 1947. All numbered USAF squadrons are assigned numbers from 1 to 999, with the block 101 to 300 being reserved for the Air National Guard. Generally speaking the numbers in the 900 block are post World War II units, they may however be consolidated units with lineage and heraldry dating back to World War II or even early as part of the Air Service. The only official source of lineage information is provided by the Air Force Historical Research Agency at Maxwell Air Force Base, Alabama. The only official sources of heraldry information are the AFHRA and the Institute of Heraldry, Fort Belvoir, Virginia.