Rishi Sunak has announced a collaboration between the UK, Italy and Japan to develop a new fighter jet that uses artificial intelligence.
The prime minister says the joint venture aims to create thousands of UK jobs and strengthen security ties.
The nations will develop a next generation fighter – due to enter service in the mid-2030s – that will eventually replace the Typhoon jet.
It is hoped the new Tempest jet will carry the latest weapons.
Mr Sunak said the partnership would "keep the country safe from the new threats that we face" as he visited RAF Coningsby in Lincolnshire on Friday.
He said: "We're one of the few countries in the world that has the capability to build technologically advanced fighter aircraft."
Work on developing it is already under way – with the aim to create a combat aircraft that will provide speed stealth, use advanced sensors and even artificial intelligence to assist the human pilot when they are overwhelmed, or under extreme stress.
It could also be flown without a pilot's input if required and could be able to fire hypersonic missiles.
But building such a complex aircraft is extremely expensive – developing the F35 jet was the most expensive programme ever undertaken by the Pentagon – so Britain has been looking for partners.
Italy was already on board, and the addition of Japan is a significant move – at a time when Britain is building closer ties with allies in the Indo-Pacific region worried about a more assertive China.
Other countries could still join the programme. France, Germany and Spain are already working together on their own separate design – as is the United States.
BAE Systems at Warton and Samlesbury will play a key role in developing Tempest in Britain. Japan's Mitsubishi Heavy Industries and Italy's Leonardo are among the other companies involved.
For the UK, this agreement is not just about security but also economics. The hope is that developing a new fighter jet could create and sustain thousands of UK jobs and open doors to more arms exports.
Ahead of the visit to RAF Coningsby, Mr Sunak said: "The security of the United Kingdom, both today and for future generations, will always be of paramount importance to this government.
"That's why we need to stay at the cutting-edge of advancements in defence technology – outpacing and out-manoeuvring those who seek to do us harm.
"The international partnership we have announced today with Italy and Japan aims to do just that, underlining that the security of the Euro-Atlantic and Indo-Pacific regions are indivisible.
"The next-generation of combat aircraft we design will protect us and our allies around the world by harnessing the strength of our world-beating defence industry – creating jobs while saving lives."
John Healey, Labour's shadow defence secretary, said his party backed the partnership but warned about training.
"Ministers must make clear how this fits with wider plans for the RAF's future, including how they will prevent delays in fast-jet pilot training," he said.
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