The UK is to join forces with Italy and Japan to develop next-generation fighter jets to respond to future security threats.
Rishi Sunak launched the programme today at RAF Coningsby, in Lincolnshire, where he saw a model of the new jet being developed.
Downing Street hopes the Tempest jets will be in the skies by 2035.
The planes are 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 other countries is hoped to share the costs and ensure the RAF can easily work with its closest partners.
Mr Sunak said the defence partnership will ensure the UK and allies are "outpacing and out-manoeuvring those who seek to do us harm".
"We're one of the few countries in the world that has the capability to build technologically advanced fighter aircraft," the Prime Minister said.
"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.”
