Twelve countries, including the UK, are set to spend more than £37bn ($50bn) over the next 10 years on a new long-range missile to protect Europe.
The Deep Precision Strike project has just been unveiled by No 10 and is due to be discussed later on Wednesday at the Nato summit in the Turkish capital, Ankara.
Sir Keir Starmer is there for his final Nato summit as prime minister. He is likely to face some criticism from US President Donald Trump for failing to set out a plan for reaching 3.5% of GDP spent on defence by 2035, a target agreed by nearly all Nato members last year.
But on Wednesday the prime minister will convene around a dozen leaders to discuss the new missile programme.
Billed as one of Nato’s most advanced weapons, it is intended to strike targets nearly 200 miles (300km) away with pinpoint accuracy, possibly extending out to 1,250 miles.
Sir Keir said the UK-led initiative would “help bring European allies together to keep Nato safe for years to come”.
Foreign Secretary Yvette Cooper said the plan was “part of a recognition that we’re in a more dangerous world”.
“This is about how we make sure we have a stronger Europe within a stronger Nato,” she told BBC Breakfast from Ankara.
But like many planned military projects in the pipeline, Deep Strike is not expected to be ready until the 2030s.
In June, US Defence Secretary Pete Hegseth announced a six-month review of the presence of US forces in Europe.
Trump has repeatedly made clear he wants Nato members to contribute more to defence spending in Europe and at last year’s Nato summit, members of the alliance agreed to spend 5% of GDP on defence and security by 2035.
Sir Keir said he was “determined” to ensure the safety of the UK and its allies, adding: “We must step up to deliver a stronger, more European Nato.”
The UK government has already committed £300bn by 2030 in the Defence Investment Plan.