Australia to buy three used Virginia-class submarines under AUKUS pact changes

It was always Australia's preference to get three second-hand submarines, a senior defence official has revealed in Senate estimates, as the government faces pressure to renegotiate the AUKUS pact.

The revelation casts a new light on changes to the agreement over the weekend, under which Australia will buy three used Virginia-class submarines rather than two used and one new.

Defence Minister Richard Marles met with US War Secretary Pete Hegseth in Singapore on Saturday, where the pair reaffirmed the AUKUS pact but announced the change to the delivery plan.

Mr Marles has argued that acquiring three used submarines in the 2030s would "streamline" an "incredibly complicated" deal.

Secretary of the Defence Department Meghan Quinn confirmed it was a "joint idea" to modify the agreement, three years after the nuclear-powered submarine pathway was announced.

Liberal senator James Paterson queried why the United States had "imposed" a new submarine on Australia.

"Because this is a joint exercise over many decades working collaboratively with an alliance partner to deliver a capability, which is significant and is very important for Australia's national defence," Ms Quinn said.

She said ongoing discussions over time had delivered the new arrangement, which would be "simpler" and "lower cost".

"Just a note that these in-service Virginia-class submarines would be in the early stage of their operation and would be available to Australia for decades after receipt of them," she added.

Vocal Labor backbencher calls for AUKUS renegotiation

Labor MP Ed Husic says Australia needs to look at renegotiating the AUKUS pact with the United States and the United Kingdom and start contemplating alternative options following the changes.

The remarks followed a Labor MP questioning the prime minister during Labor's caucus meeting earlier today, arguing the changed deal should prompt a reconsideration of the party's commitment to AUKUS.

While not confirming he was the MP who raised the issue, Mr Husic said there was clearly a need to question whether AUKUS could be delivered as promised.

"There's obviously been — this is a great understatement — but you've seen within the broader [Labor] movement a general disquiet about the nature of the deal itself.

"But putting all that aside, there's an issue about reality, and that is confronting us about whether or not we will even get the new deal that has been put to us based on what's happening in the US."

Mr Husic has pointed to challenges in American shipyards struggling to lift their rate of production of Virginia-class submarines as one clear issue in the deal, and says it is what likely provoked the change announced over the weekend.

The United States is trying to double its production rate from just over one submarine a year to more than two a year, aiming to sell submarines to Australia without setting back the growth of its own fleet.

He said the AUKUS deal needed to be renegotiated and alternative options explored.

"I think the reality on the ground will force a renegotiation. It won't be a renegotiation, it's a reality about the production rates and whether or not we'll get them," Mr Husic said.

Defence Industry Minister Pat Conroy said the government was determined to continue with the AUKUS agreement.

"We have taken our position on AUKUS to two elections. It has been put to Caucus and approved by Caucus,"

"It has been thoroughly debated at the national conference, which resolved to back AUKUS and the tens of thousands of jobs it is creating."

Coalition questions Labor commitment

The federal opposition has leapt on the comments from Mr Husic, arguing it is a sign of fracturing of support for the nuclear submarine pact.

Shadow Defence Minister James Paterson said the prime minister and defence minister should shut down dissent in Labor ranks.

"Richard Marles needs to show leadership — he needs to haul Ed Husic into line, and demonstrate that the Labor government is one hundred per cent behind AUKUS."

He said there were also significant questions about the reasoning behind the shift to three used Virginia-class submarines.

"If it is the case, as [Richard Marles] says, that this will be cheaper and simpler — then why wasn't this the plan from the beginning?"

The Greens have also called on the government to provide more details about the changed plans, arguing it lacked transparency.

Greens Senator David Shoebridge said Labor should be asking questions about the pact.

The renewed discussion of AUKUS within parliament comes as a group of AUKUS sceptics and critics launch a "public inquiry" into the pact.

The "AUKUS public inquiry", led by former Labor minister Peter Garrett, aims to mirror the processes of a parliamentary inquiry that the group argues should have taken place before the pact was agreed.

Mr Garrett and four others, including former chief of the defence force Chris Barrie, will call for public submissions and hold hearings as they examine whether AUKUS is providing value for money and can be delivered at all.

Mr Garrett said public debate about the pact was sorely needed.

"The AUKUS decision is the most momentous and expensive decision ever made by any Australian government in the modern era,"

"It is a decision that asks all of us to fully understand the implications of what is contained in that decision.

"And to provide the opportunity for Australians across the political spectrum, and all walks of life, to be heard and submit to a public discussion about this massive expenditure."