Singapore - Australia will only receive used nuclear-powered submarines from the US as part of an agreement to "streamline" the AUKUS deal, with the move branded on Sunday as a "cost-effective" measure by Defense Minister Richard Marles.
The two nations – together with the third partner in their security pact, Britain – met at Singapore's Shangri-La Dialogue, which brings together top defense officials and experts from about 45 countries.
Under the 2021 AUKUS deal, Australia is expected to receive at least three so-called "Virginia-class" nuclear-powered submarines from the US within 15 years.
Australia had been expecting to receive two used submarines and one new one, but the countries announced Saturday that all three will now be in-service vessels from the US Navy stock.
When asked why Canberra was now receiving only used equipment, Marles, who is also deputy prime minister, told reporters on Sunday it would be more cost-effective.
"In the context of a very complicated endeavor, we need to place a premium on simplicity," said Marles, who added that the submarines will also be the same model.
"I cannot overstate the significance of that, both in terms of the submariners who are operating them, but also the people who are working on them to sustain those submarines," Marles said.
"It is definitely cost-effective. And to be clear, this is a very expensive program... and so we are trying to find every cost-effective option as we walk down this path."
US shipyards struggling to meet submarine production targets
In a joint statement on Saturday, Marles, US Minister for Defense Pete Hegseth, and the UK Secretary for Defense John Healey confirmed the tweak to the submarine agreement.
"The deputy prime minister and secretaries welcomed the proposed approach to streamline Australia's acquisition of Virginia-class submarines (VCS), simplifying supply chain management, operational and maintenance requirements, and maximizing cost efficiencies," the statement said.
"This approach would enable Australia to acquire three in-service VCS in lieu of a mixture of new and in-service VCS variants."
The US Navy has 24 Virginia-class vessels, but American shipyards are struggling to meet production targets set at two new boats each year.
In the US, critics have questioned why Washington would sell nuclear-powered submarines to Australia without stocking its own military first.
The AUKUS submarine program lies at the heart of Australia's defense strategy and could cost up to US$235 billion over 30 years, according to government forecasts.