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"In 1982, the Japanese government announced that they were seeking a new warplane to succeed the Mitsubishi F-1 fighter support aircraft. This led to a project known as the Next Fighter Support Aircraft, or FS-X. The Japanese government contacted several foreign aircraft manufacturers to see if existing types could meet the FS-X requirement. At the same time, the indigenous Japanese aircraft industry was approached to see if it were practical for them to come up with a solution. Very rapidly, the contenders narrowed down to the F-16 Fighting Falcon, the F/A-18 Hornet, the Panavia Tornado IDS, and a possible indigenous aircraft. An important requirement was the use of a Japanese-built datalink system and the ability to carry the ASM-1 antiship missile.
The formal requirement was issued on November 22, 1985. The aircraft was to have the ability to carry up to four antiship missiles. In addition, the aircraft had to be able to carry 2-4 short-range AAMs and 2-4 medium- range AAMs, although not necessarily at the same time as the antiship missiles were being carried. An important requirement was a minimum combat radius of 450 nautical miles.
After looking over the responses, the Japanese Defense Agency concluded that no existing aircraft was able to meet these requirements. Only an indigenously-developed aircraft would do. The three foreign contenders complained bitterly about being ruled out in favor of an as-yet-nonexistent paper design. In addition, US and European governments became involved because of the large trade inbalances that existed between Japan and the economies of the USA and Europe, and they pressured the Japanese government for a reconsideration. As a result of the controversy, in April of 1986 the Japanese Defense Agency reissued its request, and all three foreign contenders issued revised proposals.
The question now came down to whether a co-development of an existing foreign aircraft would be selected, or if an entirely indigenous aircraft would have to be developed from scratch. The choice of an entirely new indigenous design would of course have pleased the Japanese aviation industry, but the cost would have been quite high and the project might be subject to lengthy delays due to the need to start from scratch. If a foreign design were selected instead, a considerable Japanese contribution to the project would be required. The Tornado development was eliminated at an early stage because of vague and unspecified concerns about a co-development project with European aircraft industries being somehow incompatible with Japanese security concerns. The revised F/A-18 was dropped soon thereafter because of its high cost. On September 11, 1987, it was announced that the choice had narrowed down to an indigenous aircraft, or a development of the F-15 or F-16.
On October 21, 1987, the Japanese government announced that it had ruled out the solely indigenous option, and that it had selected a development of the F-16C/D as the choice for the FS-X. The decision was undoubtedly due to a lot of pressure from the US government. The deal was also rather controversial in the USA at the time, with critics charging that the US was giving away too much technology to a competitor. Japanese Air Self Defense Force (JASDF) announced plans to acquire as many as 130 FS-Xs to replace the Mitsubishi F-1 fighter bomber.
The prime contractor for the FS-X was Mitsubishi Heavy Industries, in collaboration with General Dynamics (now Lockheed Martin). Fuji Heavy Industries and Kawasaki Heavy Industries were important subcontractors. It was agreed that 60 percent of the work would be done in Japan, with the remaining 40 percent of the work being done by American industries.
Mitsubshi was assigned the responsibility for the forward fuselage and for all final assembly, with Kawasaki supplying the central fuselage, the landing gear doors, and the engine access doors. Fuji is responsible for the radome, the air intake, the starboard wing (except for the leading edge flaps), wing root fairings, the starboard wing flaperon, vertical tail surface and horizontal tail surface. General Dynamics (later Lockheed Martin) was given the port wing (with the exception of the flaperon), the starboard wing leading edge flaps, and the rear fuselage. "