President Donald Trump’s pick for next US Ambassador to Australia has told close confidantes he will help advocate for the AUKUS submarine deal if he is approved for the Canberra posting.

At the same time Pentagon boss Pete Hegseth has declared Australia “understands” the need to increase its defence spending as he warned “allies that still fail to do their part” will face consequences.

Conservative Republican David Brat, who previously represented Virginia in Congress for five years, was nominated by President Trump on Monday to become the country’s 24th ambassador to Australia.

Figures linked to the Trump administration say that the economics professor has this week privately indicated to friends and colleagues that he supports Australia’s push to acquire nuclear-powered submarines.

“He’s certainly let it be known that if he is confirmed by the Senate as ambassador to Australia, he will be a champion for AUKUS,” one Washington-based military source tells The Nightly.

While David Brat is yet to comment publicly on his nomination as ambassador to Australia, the US Secretary of War Pete Hegseth has also expressed support for AUKUS during an overnight appearance before Congress.

Speaking before the House of Representatives Armed Services Committee, the Secretary said it was “vitally important for America’s allies and partners to step up and do their part for our collective defence”.

He said his recently renamed War Department was “prioritising increased burden-sharing in the Indo-Pacific” noting South Korea was a “model ally” by committing to increased defence spending.

“Australia likewise understands the need to increase defence spending and Canberra has taken another step with the release of its latest National Defence Strategy,” Mr Hegseth said.

“We look forward to building on that progress with our Australian allies to be able to do more in the Alliance together, move full steam ahead on AUKUS and build capability to promote meaningful deterrence”.

His prepared remarks were backed up by the Pentagon’s head of policy, Elbridge Colby who last year lead an examination into the proposed transfer of submarines to Australia to ensure the move aligned with President Trump’s “America first” agenda.

Earlier this month, the Albanese Government unveiled plans for Australia to lift defence expenditure from 2 to 3 per cent of gross domestic product by 2033, using a broader formula that also counts spending on military pensions and additional infrastructure.

South Korea, which received praise along with Israel, Poland, Finland and Baltic nations, has announced it will raise defence spending to 3.5 per cent of GDP by 2035, a level the Trump administration has previously pushed Australia to meet.

The Secretary of War said countries which had acted on calls to do more would “receive our special favour”, while warning: “not all allies have gotten the message, and where they do not step up, there will be consequences”.

During the nearly six-hour-long hearing on Capitol Hill, Secretary Hegseth regularly sparred with Democratic lawmakers as he was questioned under oath for the first time since the start of the Iran war.

Appeared alongside Chairman of the Joint Chiefs of Staff Gen Dan Caine Hegseth said the “biggest adversary we face” is the “defeatist words” of Democrats and some Republicans.

Democratic committee members in turn criticised how federal money was being used in the conflict, with the Pentagon confirming in the hearing that the war had cost the US $25billion ($35 billion AUD) so far.

Pentagon chief financial officer Jules Hurst told the committee that most of the expenses from the Iran war had been for munitions and to replace equipment, while a full assessment of the cost would be provided at a later date.