Mitsubishi is the prime contractor for modernisation of 96 Japan Air Self-Defence Force McDonnell Douglas F-4EJ Phantoms. The first updated F-4EJKai was delivered in 1989. Improvements include installation of a Westinghouse APG-66J pulse- Doppler radar as well as other avionics upgrades.
Formerly known as the FS-X, a Mitsubishi-developed derivative of the Lockheed Martin F-16, powered by the GE F110-129s, was flown for the first time in October 1995. A second prototype was flown in December 1995.
The aircraft is intended to replace the Japan Air Self-Defence Force's Mitsubishi F-1 support fighter from 1999.