The leaders of the US, UK and Australia have unveiled new details of their plan to create a fleet of next generation nuclear-powered submarines.
Under the Aukus agreement, Australia will first receive at least three nuclear-powered submarines from the US.
The allies will also work together to create a new fleet using cutting-edge technology, including reactors made by Rolls-Royce in the UK.
The pact is aimed at countering China's influence in the Indo-Pacific region.
Speaking with the other leaders in San Diego, California, US President Joe Biden stressed that the boats would not have nuclear weapons and would not jeopardise Australia's commitment to being a nuclear-free country.
Under the deal outlined on Monday, members of the Royal Australian Navy (RAN) will be embedded at US and UK submarine bases from this year to gain the necessary skills to use the submarines.
From 2027, the US and UK will base a small number of nuclear subs at a RAN base in Perth, Western Australia, before Australia buys three American Virginia-class submarines in the early 2030s - with options to purchase two more.
After that, the plan is to design and build an entirely new nuclear-powered submarine for the UK and Australian navies, called SSN-AUKUS.
This attack craft will be built in Britain and Australia to a British design, but use technology from all three countries.
President Biden said all three countries were committed to ensuring that the region would remain free and open. He was flanked by the prime ministers of Australia and the UK - Anthony Albanese and Rishi Sunak, respectively.
"Forging this new partnership, we're showing again how democracies can deliver our own security and prosperity... not just for us but for the entire world," he said.
As part of Monday's announcement, the US has also pledged a total of $4.6bn (£3.7bn) over the next few years to build its submarine construction capacity and to improve maintenance of its Virginia-class submarines.
Australia's Anthony Albanese said the submarine plan would create thousands of new jobs and marked the "biggest single investment in Australia's defence capability in all of its history".
"This will be an Australian sovereign capability, commanded by the royal Australian navy and - sustained by Australian workers in Australian shipyards with construction to begin this decade," said Mr Albanese.
He also noted that the agreement marks the first time in 65 years and only the second time in history that the US has shared its nuclear propulsion technology.
UK Prime Minister Sunak said that in the 18 months since the pact was unveiled, the challenges to global stability had only grown.
"Russia's illegal invasion of Ukraine, China's growing assertiveness, the destabilising behaviour of Iran and north Korea - all threaten to create a world codefined by danger, disorder and division."
As part of his visit to the US, Mr Sunak has also pledged to increase defence spending by nearly £5bn ($6bn) over the next two years to counter threats from hostile states.
The pact has repeatedly drawn criticism from China. Beijing's foreign ministry spokesperson, Mao Ning, last week reiterated Beijing's position that the pact risked creating an arms race and "undermines peace and stability in the Asia-Pacific region".
"We urge the United States, Britain and Australia to abandon the Cold War mentality and zero-sum game, faithfully fulfil their international obligations, and do more to contribute to regional peace and stability," he said.
Touching on the concern about the West boosting its military presence in the Indo-Pacific, US National Security Advisor Jake Sullivan insisted that Washington had no intention of creating a new Nato-like alliance.
While all three leaders have been keen to stress how the deal will strengthen their co-operation and contribute to global stability, it hasn't been without its political fallout.
In 2021, Australia scrapped a multi-million dollar submarine agreement with France in favour of the trilateral agreement - causing a political rift with Paris.
After President Emmanuel Macron pushed his unpopular pension bill through Parliament without a vote, demonstrations about the changes broke out again.