MELBOURNE, Australia – The U.S. State Department has approved Japan’s request for an upgrade package for almost a hundred of its F-15 Eagle interceptors, paving the way for the U.S. ally to upgrade its rapidly ageing fleet.

In an Oct. 29 statement, the Defense Security Cooperation Agency also said that Congress had been notified of the approval, which has an estimated cost of $4.5 billion and runs under the foreign military sales program.

The approval will allow Japan to upgrade up to 98 of its F-15J interceptors to a “Japanese Super Interceptor (JSI) configuration,” which will see the addition of an advanced electronically scanned array (AESA) radar, new mission computers and electronic warfare equipment, as well as the integration of new munitions.

The new radar will be the Raytheon AN/APG-82(v)1 multimode AESA set that is currently being fitted on the U.S. Air Force’s F-15E Strike Eagles. Japan had requested 103 radars, including six spare sets, along with 116 Honeywell Advanced Display Core Processor II mission computers and 101 BAE Systems AN/ALQ-239 digital electronic warfare systems among the suite of upgrades. The package also will include anti-spoofing GPS gear for more precise navigation, and new radios.

Japan’s request also included “aircraft and munition integration and test support,” and although the DSCA notification did not provide more details, Japan had confirmed in its mid-term defense program announcement in late 2018 that it intended to procure the Lockheed-Martin AGM-158 Joint Air-to-Surface Standoff Missile or JASSM for long-range land attack missions and integrating such weapons into its fleet of F-15s.

The prime contractor for the program will be Boeing although the notification also revealed that the Japanese F-15JSI upgrade program will have a direct commercial sale, or DCS, element. The prime contractor for the DCS portion will be Mitsubishi Heavy Industries or MHI, with Boeing being a sub-contractor in supporting integration of the FMS and DCS elements.

The Japan Air Self-Defense Force or JASDF operates a fleet of some 200 single-seat F-15J and two-seat F-15DJ Eagle. These are all configured for the air defense role with virtually no air-to-ground capability, and serve with seven different operational squadrons throughout Japan, a training squadron, and another unit in the dedicated aggressor role, acting as the adversary during training exercises.

Japan’s fleet of F-15s was built in the 1980s, mostly by Mitsubishi Heavy Industries in Japan under license and are fitted with an indigenous electronic-warfare suite and bidirectional datalink. Of these, around 90 are have been upgraded under the multi-stage improvement program that began in 1987 and saw the aircraft fitted with improved engines and countermeasures suite.

There have been further attempts at upgrading the type over the years, however due to a variety of fiscal and political reasons Japan has never managed to carry out a fleet-wide upgrade program for its F-15s, resulting in the current fleet being in several different equipment configurations.

The most recent attempt saw only a small number of F-15Js upgraded with Link 16 and Joint Helmet Mounted Cueing Systems of JHMCS from 2007, but the project was terminated after having been drastically reduced in scope following the election of a strongly pacifist government in 2009, and a planned addition of infrared-search-and-track, or IRST, systems and the conversion of a small number of aircraft to serve in the stand-off reconnaissance role was abruptly abandoned.

As such, this latest upgrade plan for Japan’s F-15 represents another opportunity to streamline the fleet in addition to keeping the type relevant for Japan’s defense needs. Notably missing from the upgrade request was a lack of further Link 16 datalinks and cockpit upgrades to a digital glass cockpit, although there is a possibility that these could come under the DCS portion of the program given MHI has had experience with the latter from the F-2 program.

Japan also appears to be continuing the development of IRST for fighters after fitting one such system on an F-15J testbed in the early part of this decade. Recent photographs posted online by Japanese plane spotters show an F-4EJ Phantom II fighter jet serving as a flying test bed with the JASDF’s test wing located at Gifu in central Japan carrying a pod on its wing with what appears to be a lens on its nose, similar to the Lockheed-Martin IRST21 developed for Boeing’s F/A-18E/F Super Hornet.

The development of an IRST, which allows the fighter to detect and engage targets at long range without having to rely on its radar and risk exposing its own position, would also be useful to Japan’s plan to develop its next-generation fighter to replace its Mitsubishi F-2s in the 2030s.

The country is also the biggest foreign buyer of Lockheed-Martin’s F-35 Lightning II Joint Strike Fighter, with the first squadron of what will eventually be a fleet of 105 F-35As and 42 F-35Bs already operational. The F-35s will replace the JASDF’s F-4EJ Phantom II and older F-15s that will not be upgraded, with the short take-off vertical landing F-35Bs earmarked for future operations aboard Japan’s Izumo-class helicopter destroyers.

Mike Yeo is the Asia correspondent for Defense News.

More In Asia Pacific