McDonnell F-4EJ Kai Phantom II

Last revised February 26, 2000

F-4EJ Kai was the designation applied to existing Japanese-built F-4EJ fighters that were upgraded in a modernization program initiated in July of 1984. The goals of the program were to bring JASDF F-4EJs up to standards appropriate for the 1990s and to extend their service lives well into the 21st century.

The F-4EJ Kai (the suffix "Kai" means "extra" or "augmented") is fitted with the Westinghouse AN/APG-66J pulse-Doppler radar, which is much smaller and lighter than the original APQ-120, but has more operating modes with better lookdown, shootdown capability. Externally, the installation of the new radar can be distinguished by the presence of a new radome which has fore and aft strengthening ribs.

The F-4EJ Kai has a a new central computer, a Kaiser heads-up display, a Hazeltine AN/APZ-79 IFF system, and a license-built Litton LN-39 inertial navigation unit.

A new J/APR-6 radar homing and warning system is fitted. Twin aft-facing radomes for this system are mounted on the fin tip and forward-facing antennae are mounted on the wingtips. A new, much taller UHF blade antenna is mounted on the dorsal spine, and the lower UHF antenna on the undercarriage door is larger in size. These are about the only externally-visible distinguishing points between the F-4EJ and the F-4EJ Kai.

The aircraft often carries a 610-US gallon F-15 fuel tank on the centerline. This tank is stressed to take higher g-loads than was the original F-4 centerline tank. The F-4EJ Kai can also carry the Westinghouse AN/ALQ-131 advanced multimode electronic countermeasures pod. This pod has a wide range of modules and has reprogrammable software which make it capable of quickly countering new threats.

The F-4EJ Kai can launch the AIM-7E/F Sparrow and the AIM-9L/P Sidewinder air-to-air missiles. In addition, the F-4EJ Kai can carry and launch the Mitsubishi ASM-1 antiship missile. This missile has a launch weight of about 1345 pounds and is powered by a Nissan Motors solid rocket engine. It has midcourse guidance provided by an inertial system acting in conjunction with a radar altimeter which maintains an altitude just above the tops of the waves during the final run-in to the target. Terminal guidance is provided by an active radar seeker mounted in the nose. A 440-pound high-explosive warhead is carried.

Plans to fit slatted wings to the F-4EJ Kai were ruled out on the basis of cost.

The first F-4EJ Kai flew on July 17, 1984, and the 306th Hikotai accepted its first example on November 24, 1989.

Fourteen RF-4EJs had been built by McDonnell for the JASDF. In parallel with the Kai upgrade of the F-4EJ fighter, the existing RF-4EJs were also refurbished and upgraded as RF-4EJ Kai. The RF-4EJ Kai incorporated many of the same modifications as did the F-4EJ Kai, and had the AN/APQ-99 radar replaced with a new Texas Instruments AN/APQ-172 radar. A new inertial navigation system was fitted, as well as an infrared reconaissance system, digital cockpit displays, and a VHF radio to replace the existing UHF system.

Because the JASDF perceived a need for more RF-4EJs, a contract was given to Mitsubishi Electric for the conversion of 17 F-4EJ fighters to reconnaissance configuration. Some confusion has resulted from this conversion, since these aircraft are also designated RF-4EJ Kai. They retained the original radar, RWR, and navigation set of the F-4EJ, and they retain the complete armament capability of the F-4EJ. These converted fighters are being equipped with digital avionics, including a Texas Instruments APQ-172 radar, a heads-up display, a podded Thomson-CSF Raphael SKAR, and a large Elint pod developed by Mitsubishi. The first example converted was 37-6406.

The first F-4EJ Kai flew in 1984, and the 306th Hikotai accepted its first example on November 24, 1989. It had originally been planned to upgrade 110 of the 125 surviving F-4EJs to Kai standards, but this was later changed to only 96. Seventeen of the remaining 29 were to be adapted to the reconnaissance role under the designation RF-4EJ Kai. 12 were retired. Three JASDF squadrons are currently equipped with the F-4EJ Kai (306 Hikotai at Komatsu, 301 Hikotai at Nyutabaru, andd 802 Hikotai at Naha), and they should remain with the JASDF until well after the year 2000. Although the upgrade to the F-4EJ has prolonged the service life of Japanese Phantoms, they cannot be expected to continue on indefinitely and the replacement of the F-4EJ Kai by some more modern fighter aircraft will soon be necessary.

The following JASDF serial numbers are known to have been converted to F-4EJ Kai standards:

17-8302, 27-8305, 27-8306, 37-8308, 37-8312/8324, 47-8328/8334, 47-8337/8342, 47-8345, 47-8346, 47-8348, 47-8351/8357, 47-8360, 47-8362, 47-8366, 47-8367, 47-8369, 57-8375, 57-8377, 67-8378, 67-8379, 67-8381, 67-8384, 67-8386/8391, 77-8394, 77-8395, 77-8398/8402, 77-8404, 87-8407, 87-8410, 87-8411, 87-8413/8415, 97-8416, 97-8417, 97-8420/8427, 07-8428, 07-8431, 07-8434/8436, 17-8437/8440.


  1. McDonnell Douglas Aircraft Since 1920: Volume II, Rene J. Francillon, Naval Institute Press, 1990.

  2. McDonnell F-4 Phantom: Spirit in the Skies. Airtime Publishing, 1992.

  3. The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.

  4. United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian, 1989.

  5. The Illustrated Encyclopedia of Aircraft Armament, Bill Gunston, Orion, 1988.

  6. Japanese Self Defence Force Air Arms, Riccardo Niccoli, Air International, Vol 50 No 1 (1996).

  7. Koku Phantom, Yoshitomo Aoki, Air Forces Monthly, March 2000.

  8. F-4EJ Kai serials from Michel Klaver