The Prime Minister said that a defence partnership with Italy and Japan to develop next-generation fighter jets will help “keep the country safe from the new threats that we face”.
Downing Street aims for the jets, called Tempest in the UK, to take to the skies by 2035 and serve as a successor to the RAF Typhoon.
They are being developed in response to military bosses’ fears that air dominance is being threatened.
Rishi Sunak launched the first major phase of the programme during a visit to RAF Coningsby, in Lincolnshire, on Friday.
Mr Sunak was shown Typhoon aircraft and went into a hangar to view a model of the Tempest jet that is being developed.
He told reporters the announcement of the defence partnership was “incredibly important”.
“That’s important because it means we can keep the country safe from the new threats that we face.
“It also adds billions to our economy and supports tens of thousands of jobs across the country.
“But it’s also good for our international reputation.
Mr Sunak said that the defence partnership will ensure the UK and allies are “outpacing and out-manoeuvring those who seek to do us harm”.
Ahead of the visit, he 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 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.”
The jet is expected to be able to fly faster than the speed of sound, and have the capability of firing hypersonic weapons in the future.
Working with the allies is hoped to share the costs and ensure the RAF can easily work with its closest partners, with the new Tempests being compatible with other Nato partners’ jets.
The partnership merges the UK and Italy’s future combat air system (FCAS) projects with the Japanese F-X programme.
Ministers hope that other countries may buy into GCAP in due course.