US$12 billion (A$15 billion) is not a lot of money for developing a fighter jet. But it turns out to be a steep bill if you build only 90 units.

Yet Japan has decided it has little choice but to spend that money to create a combat aircraft for the 2030s. The government is going ahead with its F-X program, though work has not passed what is usually regarded as the critical point of commitment, the launch of full-scale development. It is close, however.

Lockheed Martin will backstop Mitsubishi Heavy Industries (MHI) in overall development of the F-X, according to a defence ministry announcement made on 18 December, but other companies from the UK and the US will help with propulsion and avionics. The F-X will almost certainly have strong technological links with the British Tempest fighter program, which has a similar timescale for entry into service.

Lockheed Martin or its rival Boeing was always most likely to be chosen as the lead technology support company to help MHI, because Japan relies on the US for protection. The other contender was BAE Systems.

The development budget hasn’t been announced but it was leaked to the Kyodo news agency and the Tokyo Shimbun newspaper: at least ¥1.2 trillion (A$15 billion). This is more than the A$11 billion that South Korea is budgeting for its KF-X fighter, but modest compared with the US$72 billion (in fiscal 2012 dollars) that the US expects finally to spend on F-35 development.

The problem is that Japan is reportedly aiming to build only 90 F-Xs. If so, the development cost per aircraft will be about A$170 million—an enormous amount even if some of that is the result of inflation. Unit production costs should be spectacular, since the fighter will be unusually large and its factories won’t get far down the learning curve before the program finishes. Also, Japan likes to build aircraft slowly (and therefore inefficiently), to keep factories working.

The defence ministry in Tokyo has been pushing and preparing for more than 10 years to build an indigenous aircraft to replace the MHI F-2 strike fighter. The government, after considering direct importation or collaboration in foreign programs, decided in 2018 to go ahead with a Japan-led effort.

It had good reasons for doing so, though the decision will have to be judged finally against the unit cost of each aircraft. The three best justifications for developing the F-X are that Japan wants full control of the configuration, the next US fighters won’t be available for export, and Japan needs a design that may not suit other countries.

And, no, just buying more F-35s was never a likely option. Japan wants the first F-X to enter service in 2035, by which time the F-35 won’t be a modern fighter: it will have been operational for 20 years and clocked up 34 years since entering full-scale development.

Also, arms importers dislike the control over equipment configuration wielded by supplier countries, either contractually or by withholding intellectual property. This is especially a problem for a country, such as Japan, that develops its own airborne weapons and sensors and wants freedom to integrate them.

Nonetheless, Japan has previously shrugged and chosen the best that the US has to offer: the F-4 Phantom in the late 1960s and the F-15 Eagle a decade later. But the US refused to supply the F-22 Raptor and cannot be expected to export its forthcoming fighters as soon as Japan needs them, if they are ever exported at all. They are still mostly secret.

Finally, the defence ministry’s studies early last decade came up with an awkward conclusion: that Japan should operate very big, twin-engine fighters to provide sufficient range and endurance. Smaller fighters could be afforded in greater numbers, but, since they would soon run out of fuel, fewer would be available on station.

The result is that the ministry’s F-X design concepts are enormous: larger than the F-22, which has an empty weight of 19.7 tonnes. (The F-35A, which is not a small aircraft, is only two-thirds as heavy as the F-22.) The F-X is shaping up as so a big a brute that I have suggested the nickname ‘Godzilla’.

The size decision is awkward, not only because bigger aircraft cost more to develop, but because Japan cannot rely on other countries agreeing as partners to build something similar. The two programs into which the F-X could have been merged were the UK’s Tempest and (apparently never seriously considered) the French–German–Spanish Future Combat Air System. Early concepts for both have indeed been large, but neither is close to program launch and either could easily be trimmed before a final design is chosen. Japan wants to get moving now.

Still, Japan will probably save some money by sharing systems with the Tempest. After long and often unsatisfactory experience in multinational aircraft development, London has determined that it won’t spend years in negotiations with partners to agree on developing a common aircraft that none would be happy with. Instead, the model is an invitation for other countries to cooperate as far as suits them. They would not need even need to use the same airframe. This is good for Godzilla.

For example, Japan can build its big, bespoke airframe but use an engine that can be developed by its own IHI Corporation and Rolls-Royce, and also be used in the Tempest. Indeed, Rolls-Royce has proposed exactly that, noting that Japan has useful materials technology.

Britain and Japan are already working on applying an advanced radar technology, element-level digital beam forming, to aircraft. And they are developing a version of the MBDA Meteor missile with an active, electronically scanned array.

Still, Japan has awarded its first prize to Lockheed Martin, which will work with Northrop Grumman in supporting MHI on the overall integration of the F-X. Lockheed Martin has become the most practiced of any company in supporting foreign fighter development: it stood behind MHI in developing the F-2 and is doing the same job with Korea Aerospace Industries on the KF-X.

Since finalisation of a concept design has been awaiting input of the top-level integration partner, F-X development cannot yet be fully launched. But the parliament this month allocated ¥73.1 billion to the program for the fiscal year beginning April 2021, suggesting that it is about to get fully underway.