Before forming the Japanese Self-Defense Forces after World War II, Japan did not have a separate air force. Aviation operations were carried out by the Imperial Japanese Army Air Service and the Imperial Japanese Navy Air Service. Following World War II, the Imperial Japanese Army and Navy were dissolved and later replaced by the JSDF with the passing of the 1954 Self-Defense Forces Law, with the JASDF as the aviation branch.
Major units of the JASDF are the Air Defense Command, Air Support Command, Air Training Command, Air Development and Test Command, and Air Materiel Command. The Air Support Command is responsible for direct support of operational forces in rescue, transportation, control, weather monitoring and inspection. The Air Training Command is responsible for basic flying and technical training. The Air Development and Test Command, in addition to overseeing equipment research and development, is also responsible for research and development in such areas as flight medicine.
The Air Defense Command has northern, central, and western regional headquarters located at Misawa, Iruma, and Kasuga, respectively and the Southwestern Composite Air Division based at Naha on Okinawa. All four regional headquarters control surface-to-air missile units of both the JASDF and the JGSDF located in their respective areas.
The JASDF maintains an integrated network of radar installations and air defense direction centers throughout the country known as the Basic Air Defense Ground Environment. In the late 1980s, the system was modernized and augmented with E-2C Hawkeye airborne early warning aircraft. The nation relies on fighter-interceptor aircraft and surface-to-air missiles to intercept hostile aircraft. Both of these systems were improved from the beginning of the late 1980s. Outmoded aircraft were replaced in the early 1990s with more sophisticated models, and Nike-J missiles have been replaced with the modern Patriot PAC-2 and PAC-3 system. The JASDF also provides air support for ground and sea operations of the JGSDF and the JMSDF and air defense for bases of all the forces. Base defenses were upgraded in the late 1980s with new surface-to-air missiles, modern antiaircraft artillery and new fixed and mobile aircraft shelters.