The US is set to sell Australia at least three, and up to five, Virginia-class nuclear submarines under the trilateral AUKUS partnership that also includes Britain.
But the president's budget proposal for 2025 cuts one of the submarines from the production line, raising doubts over whether second-hand vessels could be sold to Australia in the early 2030s without reducing the firepower of the US fleet.
Democrat congressman Joe Courtney, who co-chairs the bipartisan AUKUS working group in the US, said the proposal was not a fatal blow.
The budget still needed to work its way through the US Congress, which has oversight of spending, Mr Courtney said.
A year ago, Mr Albanese stood with Mr Biden and Mr Sunak at the Point Loma naval base in San Diego. (AP PHOTO)
"I don't think this is a fatal blow to AUKUS ... we've already spent and purchased parts for the second 2025 sub which is the sub that is in play here," he told ABC Radio on Thursday.
"There's going to be a tremendous amount of concerning questions when the budget hearings take place."
Previous decisions to cut back on submarines by former presidents Barack Obama and Donald Trump were reversed by Congress, he said.
Australian Defence Minister Richard Marles insisted the AUKUS partnership was a "rock solid commitment to Australia" amid the doubts.
Thursday marks one year since Prime Minister Anthony Albanese stood alongside British counterpart Rishi Sunak and US President Joe Biden to announce how Australia would acquire nuclear-powered subs under the $368 billion pact.
The US submarine industrial base is already under pressure, with lawmakers sounding the alarm about the strain.
Republican lawmakers previously moved to block legislation that would allow the US to send nuclear-powered submarines to Australia as leverage to boost military spending.
There are also concerns the agreement could be torpedoed if Donald Trump becomes president, given Mr Biden signed the deal.
One year ago, President Biden, Prime Minister Albanese, and Prime Minister Sunak announced the way forward on AUKUS. Ambassador Kennedy recently visited Osborne Naval Shipyard in Adelaide, South Australia and reflected on the one-year anniversary of the leaders' announcement:… — U.S. Embassy Australia (@USEmbAustralia) pic.twitter.com/9Nxub7h00rMarch 13, 2024
But Mr Marles dismissed suggestions the US was walking back from its pledge to AUKUS.
"There is absolutely a rock-solid commitment to Australia," he told ABC News on Wednesday.
"The fact that the American industrial base is stretched in 2024, as it was in 2023 when we made this announcement, is not news.
"It formed part of the landscape against which this arrangement was agreed a year ago."
US Ambassador to Australia Caroline Kennedy marked the anniversary in a post on social media platform X.
"(AUKUS is) going to bring thousands of new and exciting jobs, the most advanced technology, and the most exciting opportunities to young Australians, Americans and British, all working together to keep this region and our countries safe," she said in a video.
The ambassador recently visited Osborne Naval Shipyard in Adelaide, where the new SSN-AUKUS submarines will be constructed for delivery in the early 2040s.
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