Australia could still buy five US submarines if needed, defence minister says

Australia's Defence Minister Richard Marles says the United States remains open to providing up to five Virginia-class submarines under AUKUS.

Mr Marles said on the weekend that Australia was planning to buy just three second-hand Virginia-class submarines from the US.

The defence minister says the government remains confident it can bridge the gap to Australia's planned new AUKUS submarines under the shake-up.

Defence Minister Richard Marles says the United States is still open to providing Australia with up to five Virginia-class submarines, but has declared the government remains confident it can bridge the gap to the next-generation AUKUS submarines with just three.

Over the weekend, Mr Marles and his US and United Kingdom counterparts announced Australia was planning to buy three second-hand Virginia-class submarines, instead of one new submarine and two second-hand ones, from the United States.

Some critics say the move exposes deep flaws in the ambitious AUKUS push, while the opposition has vowed to interrogate the shift at Senate estimates this week in Canberra.

Australia is planning to buy second-hand Virginia-class submarines. (Reuters: Brian Snyder)

Analysts have also asked why language previously adopted by the three nations — which said Australia would acquire between three and five Virginia-class submarines — appeared to have "disappeared" from the most recent statement.

Mr Marles told the ABC in Singapore that there were "no changes" to the AUKUS deal, and it was "the same arrangement it has always been", indicating Australia could still move to purchase a further two submarines if they were needed.

But he also said that the government was intent on "getting the Australian build up and running as soon as possible" to ensure that the two additional Virginia-class submarines were not necessary.

"It's the same arrangement it has always been, but we want to see that first Australian-built submarine come off the production line … that's the key thing here.

The US, UK and Australia have announced they will "streamline" the purchase, with Australia no longer buying any new submarines, and acquiring three second-hand submarines.

While the government remains confident the US will sell the submarines to Australia next decade, there is no guarantee it will happen: the White House will have to sign off on the sale, and will only do so if it can lift stubbornly low submarine production rates at US shipyards.

Some analysts have also questioned whether the shift unveiled on the weekend would reduce Australia's submarine capability, because t