A surprising defence-technology partnership is emerging between Japan and the UK. The cooperation is mostly preliminary but not at all basic: the two countries are working together on some of the most challenging systems used in combat aircraft. And there’s good reason to think they’ll pool resources on more such programs.

For Japan, the UK is an obvious high-capability partner for technology areas in which the US will not share its knowhow. The British no doubt see Japan as an alternative to France and Germany for sharing development costs, especially in the combat-aircraft field. Here and there, we also see signs that Japan has technology that the British would regard as valuable.

This development should be welcomed by anyone who wants to see a stronger Japan, one that gets more capability from its defence budget.

On 2 February, the UK and Japanese governments made what appears to have been their first joint mention ^[1] of an ambitious potential joint project that Tokyo had briefly discussed in Japanese text in 2018. Called ‘Jaguar’, it’s officially said to be a universal radio-frequency (RF) system. It would presumably be intended for the Japanese F-X ^[2] and UK-led Tempest ^[3] fighter programs.

Separately, Japan revealed in September that it and the UK had been working together on a powerful radar technology; we can assume this would be integral to Jaguar. The UK and Japan are also cooperating on developing an advanced version of a far-flying air-to-air missile. And Rolls-Royce has proposed cooperative development of a single engine type for the F-X and Tempest programs, which are running on somewhat parallel timescales.

All of this wouldn’t have been imaginable only a few years ago, when Japan basically didn’t cooperate with anyone in developing defence equipment. The sudden partnership with Britain has become possible because in 2014 Japan began to emerge from its military-technology shell. In that year it ended a self-imposed ban on arms exports, which had largely prevented it from joining collaborative programs.

A country can hardly cooperate in developing and making defence systems if it can’t send defence parts to the partner. So Japan has often wasted defence funds by working on technologies that friendly countries were also developing. We can now expect the Japanese defence-technology budget to stretch further.

In fact, a crack appeared in the export ban in 2013, when the government allowed Kawasaki Heavy Industries to send engine parts to Rolls-Royce for the Royal Navy. They were parts designed by Rolls-Royce, but the UK propulsion giant had stopped making them. The Royal Navy still needed them, so Japan agreed to supply—causing a few eyebrows to rise.

Before this there had been one, much larger exception to the export ban: Japan worked with the US in developing the Raytheon SM-3 Block 2A anti-ballistic-missile interceptor.

We might imagine that the US would be Japan’s preferred partner for just about any defence-technology effort—and indeed it would be, if only it were willing to share its secrets. In general, the US prefers to pay the whole cost of its most advanced work, initially keeping the resulting capability to itself and often not letting even close allies know what it’s up to.

That policy left Japan with only two strong alternatives: the UK and France. It may have preferred the UK not only because of specific technological strengths but also because of the unusually close UK military connection with the US. The choice doesn’t stop Japan from working with other countries, and indeed since 2014 it has done a little defence research with France and (in relation to marine hydrography) Australia.

The ambition of Jaguar development, which is subject to an ongoing UK–Japanese feasibility study, shows how high Tokyo is aiming in international collaboration. Jaguar would be an advanced piece of kit. Since it is described as a ‘universal’ system, it would probably be a four-in-one set-up, combining the functions of radar, passive radio-frequency detection, jamming and communications. Japan first outlined ambitions for just such an apparatus in 2004.

Traditionally, a separate system provides each of those four functions in an aircraft, though they have always had to be designed not to interfere with each other and there has been a trend towards integration, notably in the Lockheed Martin F-35 Lightning. Consolidating functions can reduce bulk and weight—for example, by sharing antennas—but the integrated system is necessarily complex and difficult to engineer.

A project on radar antenna design also reveals the scale of ambition in UK–Japanese work. The two countries have already been working together in this area, on a specific technology called element-level digital beam forming ^[4], or DBF. This concept has been applied to surface radars (reportedly including the Australian CEA Technologies radars on Anzac-class frigates) but not to aircraft radars, which is where Japan and the UK want to take it.

With element-level DBF, the entire face of an antenna can constantly receive signals in many directions, limited mainly by processing power. More conventional radars look in different directions sequentially or by splitting their antennas into segments; either way, they lose sensitivity. A radar that continuously receives in many directions has longer range and a better chance of picking up stealthy targets.

Japan has strong radar technology. It was the first country to field a radar with an active, electronically scanned array in a fighter: the Mitsubishi Electric J/APG-1 in the Mitsubishi Heavy Industries F-2, which entered service in 2000. Japan may also be the first to put that high-performance technology into the seeker of an air-to-air missile. For that job, it has chosen to modify the MBDA Meteor, a ramjet weapon that has been developed in a multinational program led by the UK. The British are helping with the upgrade. (They also provide test ranges far removed from Chinese electromagnetic listening gear.)

Although Rolls-Royce is one of the world’s three main aero-engine companies (the other two are American), it could probably learn a thing or two from Japan. In preparing for the F-X program, Japan has been working on identifying materials that can cope with extremely high temperatures, which would improve efficiency, and on squeezing down the diameter of a fighter engine to reduce drag.

As for other systems that could go into both the F-X and Tempest, Japan and the UK are still talking. Lockheed Martin will be Mitsubishi’s overall technological supporter for the F-X, helped by Northrop Grumman. But the program will run into the problem that the US companies can’t share all the information that Japan needs. Again, the solution may come from the other island nation that flanks Eurasia.