As the US, Taiwan and Australia struggle to assemble forces to face the challenge of a rapidly arming China, Japan is planning to discard good equipment that could be kept in service.

It proposes to throw away more fighters than are in all of Australia’s air combat squadrons, and it’s sticking with a policy of retiring submarines long before other countries would regard the vessels as worn out.

Fighters and submarines would be central in any war to defend Taiwan. Fighters would intercept bombers and other strike aircraft trying to get within weapon range, and they’d provide protective cover to friendly forces.

Fighters Japan could choose to keep are F-15 Eagles. They’d need deep modernisation, but Japan is already running an excellent upgrade program for some F-15s it plans to retain.

Money to upgrade more should be available as Tokyo lifts defence spending to 2% of GDP by 2027 from a long-standing limit of 1%. A defence build-up plan published in December is clearly not spending all that money.

Indeed, suspending equipment retirements and extending manufacturing programs are relatively easy ways to usefully spend a rising defence budget while officials and service officers work on complex new programs that won’t produce results for many years.

The potential addition to Japanese air combat capability is huge: 132 F-15s that, instead of being scrapped or probably relegated to training, could have advanced avionics and weapons and be fully fit for the front line.

Japan has 200 Eagles, survivors of 213 bought in the 1980s and 1990s from Boeing predecessor company McDonnell Douglas, and Mitsubishi Heavy Industries (MHI). Most are F-15Js, single-seaters similar to F-15Cs used by the US Air Force, and the rest are two-seat F-15DJs, equivalent to US F-15Ds.

About half of Japan’s F-15s were delivered without a 1980s upgrade called the ‘Multi-Stage Improvement Program’ (MSIP). The other half got the MSIP features which included wiring to support the Raytheon AIM-120 AMRAAM air-to-air missile. So Japanese MSIP F-15s are easier to upgrade, and most have already been upgraded once.

Now the country is four years into a second upgrade program that is lifting MSIP F-15Js to a new standard called F-15JSI, for Japan Super Interceptor. In important respects it matches the hot Eagle version in production for the US Air Force, the F-15EX. Note that the unstealthy F-15, offering high flight performance and able to carry a large load, is still in demand by the USAF, Qatar and, persuasively, Israel.

For situational awareness and targeting, upgraded Japanese F-15s will have thoroughly modern Raytheon APG-82 radars and BAE Systems ALQ-250 Epawss passive-radio outfits. They will carry a probably large load of AMRAAMs (the Ministry of Defense in Tokyo declines to say how many), plus the highly capable Mitsubishi Electric AAM-4B air-to-air missile. Later, the AAM-48’s intended far-flying successor, the Anglo-Japanese JNAAM, will probably appear on F-15JSIs.

Adding strike to their traditional air-superiority role, F-15JSIs will also carry Lockheed Martin AGM-158 Jassm air-to-surface missiles of an undisclosed version.

The F-15JSI is likely to be competitive against the Shenyang Aircraft J-16, the fighter that Aviation Week analysts estimate China is building fastest. The upgraded Japanese fighters would certainly be powerful tools against H-6 bombers and their salvoes of cruise missiles.

Japan’s remarkably extensive F-15 upgrade work is costing just ¥3.5 billion (US$27 million) per aircraft, the Defense Ministry says. That compares with the US$80-90 million fly-away cost of a new F-15EX or Lockheed Martin F-35A Lightning II.

The problem? Only the 68 F-15Js of MSIP standard are to be modernised. The pre-MSIP F-15Js and F-15DJs are to be disposed of and replaced with F-35s. And the 30-odd MSIP F-15DJs are presumably intended to become just training aircraft as their combat competitiveness fades.

Yet the entire Japanese F-15 fleet could be upgraded and retained—an opportunity that seems all the more stark when one considers that the US Air Force is struggling to keep a sufficient fighter force.

The Defense Ministry says studies by the USAF and Mitsubishi show that the country’s F-15 force is theoretically capable of serving until the mid-2060s. Most of these fighters have not been flown a lot.

If Japan chose to upgrade and keep them all, it could still receive the 105 F-35s intended to replace the pre-MSIP F-15s. The new aircraft are due to arrive from 2034 to 2038, but accelerating orders is surely a possibility.

So, the fighter fleet, which is now intended to remain at its current level of about 330, could grow by about a third. The effective improvement would be greater than that because the MSIP F-15DJs would be modernised.

To achieve this higher force level, MHI and its system suppliers, notably Raytheon and BAE, would have to step up production. That could be a challenge.

The Japan Air Self-Defense Force would have to attend to the usual measures associated with expanded air power—finding more pilots, technicians and ground facilities.

The easiest decision for Tokyo is to extend the JSI upgrade to the MSIP F-15DJs which would require just a little more engineering, exploiting work already done for the two-seat F-15s being built for Qatar and the USAF.

Going further to also upgrade the pre-MSIP F-15Js and F-15DJs would add only a little more complication, industry executives tell me, even though Japanese policy discussion tends to treat those aircraft as incurably unfit for improvement because of their lack of MSIP features. A reasonable guesstimate is that their upgrades might each be up to US$4 million more costly but they’d still be bargains.

That increment would allow for the possibility that the oldest aircraft, when opened up for modernisation, could turn out to have unexpected problems, such as corrosion.

A compensating effect of modernising more aircraft would be the fall in unit costs to be expected from an expanded and accelerated program.

As is common in fighter fleets, Japan’s earliest F-15s are a good deal more worn than the rest because they were used intensively for training as the type was introduced about four decades ago. Maybe 30 to 40 are in that category, says a source familiar with the fleet.

That should not exclude them from upgrades since fleet usage could be managed to hold down flight hours on those aircraft. They would still be fully useful in war.

Japan puts great emphasis on stability of work at defence factories, with the usual result that its aircraft production programs run at low and uneconomical rates and equipment keeps dribbling into service long after it ceases to represent advanced design. This is becoming more unacceptable as the risk of war rises.

Conveniently, a stepped-up F-15 upgrade program could deliver results fast and still keep factory managers happy. MHI is likely to begin volume production of Japan’s next fighter in cooperation with British and Italian companies in 2031. So, an F-15 modernisation effort would ideally be wrapped up in 2030. That would be possible if the current work ramped up between now and 2027 to a steady rate of three aircraft a month, incidentally helping MHI to build up the workforce skills it would need to make future fighters.

It’s difficult to think of how Japan could more economically and rapidly improve its air force, especially in the risky 2020s.