Deputy Prime Minister Richard Marles and UK Secretary of State John Healey have inked a 50-year agreement to strengthen ties around the AUKUS nuclear submarine agreement.
AUKUS, formed with the UK and US in 2021 amid China's rising military ambition, is designed to enable Australia to build and deliver its own nuclear-powered attack submarines in the early 2040s.
But the future of the $560 billion deal has been under a cloud since the Trump administration initiated a 30-day review to examine if it meets its "America-first" criteria.
Mr Marles expressed confidence about the US's ongoing involvement in the partnership, a sentiment echoed by Mr Healey and UK Foreign Secretary David Lammy.
Trade Minister Don Farrell denied the so-called Geelong treaty risked annoying the US, arguing it did the opposite.
"The message that the Americans will get out of this is that the other two parties to AUKUS are very, very supportive of the continuation of the project," he said.
The coalition has backed the bilateral agreement but opposition foreign affairs spokeswoman Michaelia Cash said it raised questions.
"Was the US brought in on this? Did they know about it? What was their response to it?" she said.
Maritime security expert Jennifer Parker, who served for more than 20 years with the Royal Australian Navy, said media and commentators were "reading way too much" into the timing of the treaty.
She noted the bilateral agreement was first announced at a trilateral AUKUS meeting in the UK in September, attended by the then-US Secretary of Defense Lloyd Austin.
"It's the hard work of nine months of treaty negotiations to end up in this spot," the Australian National University expert associate told AAP.
"The announcement, in the midst of the US review, is helpful to stabilising some of the conversation around AUKUS."
Although details of the treaty will remain sheltered from public view until it is tabled in federal parliament, Ms Parker said it seemed to deal with elements of AUKUS likely to differ from the US review.
The treaty appeared to primarily focus on phase three of the trilateral deal, which includes the UK transferring nuclear-powered submarine capability to Australia with US permission.
Australia will pay $5 billion to support British industry in designing and producing nuclear reactors to power the future AUKUS-class subs.
It is separately slated to acquire at least three Virginia-class nuclear-powered submarines from the US in the early 2030s.
Ms Parker said the US review was unlikely to be "catastrophic" for AUKUS as it was significantly in its interest.
But she acknowledged there could be some "tweaks around the edges".
"We know the current US administration wants to put their own stamp on each deal," the defence analyst said.
"I don't think they will, but if the US refuse to sell us submarines in the 2030s, that doesn't mean AUKUS has failed.
"It means there's a capability gap between Australia's building of SSNs (Australia's nuclear-powered submarines) and the phase-out of the Collins class."
With signing formalities done and dusted, Mr Marles, Mr Healey, Mr Lammy and Australian Foreign Minister Penny Wong toured the HMS Prince of Wales in Darwin amid Talisman Sabre exercises.
The war games, which began on July 13, encompass more than 35,000 personnel from 19 militaries across three weeks.
The HMS Prince of Wales is the first UK aircraft carrier to visit Australia since 1997.
"As threats are increasing, partnerships like the UK and Australia matter more than ever," Mr Healey told reporters on Sunday.
"By exercising together and being more ready to fight, we deter better together."
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