The head of Australia's AUKUS task force says China's military expansion justifies the purchase of new nuclear-powered submarines, while reassuring Australians the nuclear reactors on board the vessels will be safe.

"The government made a clear decision that the region had changed, it had changed for the worse," Vice Admiral Jonathan Mead told 7.30.

"It had become less stable, more fragile, and we needed a capability that could defend Australia."

Vice Admiral Mead has spent 18 months producing a road map for government of the extremely complex defence program.

While Prime Minister Anthony Albanese did not mention China in his announcement of the details of the AUKUS program in San Diego, Vice Admiral Mead acknowledged the impact of China's rapid militarisation.

"We recognise that there has been reclamation of land in the South China Sea and the military modernisation of islands there," Vice Admiral Mead said.

"A whole bunch of factors have played into this."

New sub design is '70 per cent' complete

Vice Admiral Mead spoke with 7.30 hours after the announcement, attended by Mr Albanese, United States President Joe Biden and United Kingdom Prime Minister Rishi Sunak.

The AUKUS deal promises to deliver Australia between three and five US Virginia-class nuclear-powered submarines, beginning in the 2030s.

Another eight boats of a new design called the SSN-AUKUS, to be built in Australia following a UK design, will follow.

Asked why Australia would introduce another class of submarine into its fleet beyond the Virginia class, potentially introducing extra complexity and cost, Vice Admiral Mead said: "The US are ceasing production of the Virginia-class submarine in the early 2040s.

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Duration: 7 minutes 7 seconds7m

"It was clear that for us to continue down that pathway, either by building our own Virginia-class submarines or by continuing to acquire, would not be a sustainable capability," he said.

Vice Admiral Mead said Australia was up to the task of building its own nuclear-powered boat and the design work was well advanced.

"SSN-AUKUS is actually quite mature in the design, it's about 70 per cent mature," he said.

"The US will incorporate key weapons and combat systems into that submarine. The UK are very much looking forward to that."

'Highest standards of safety'

Australia is set to become the second country, after the UK, to gain access to the US nuclear submarine technology, which relies on highly enriched uranium.

Vice Admiral Mead was asked, "why should Australians trust that these nuclear-propelled boats will be safe?"

"The US and UK have an unblemished record with their nuclear reactors," he told 7.30.

"They've operated over 500 nuclear reactors in 70 years. They've travelled 240 million kilometres, 300 times to the moon and back. That unblemished safety record we intend to emulate."

He added that the nuclear reactors which power the submarines will be "welded, shielded and sealed" — not to be opened over the three-decade life spans of the boats.

"We will uphold the highest standards of safety — safety of the crew, safety of the community, protection of the environment," Vice Admiral Mead said.

'Strong support' from Congress

President Joe Biden said on Tuesday the provision of Virginia-class submarines to the Australian navy still required approval from the US Congress. This follows concern from senior US politicians that the domestic industry would be compromised if it had to supply submarines to another country.

As part of the AUKUS deal, Australia will pay the US and the UK $3 billion over the next four years to support the countries' domestic production pipelines.

Asked if Australia had needed to buy US support with "cold hard cash," Vice Admiral Mead said Congress was "looking for our commitment to be part of a trilateral partnership".

"From the feedback that I get, we're getting very strong support from Congress," he said.

The naval chief said collaboration with the US would help generate the skilled workforce Australia needed to start building nuclear submarines in South Australian shipyards by the early 2030s.

While the details of the AUKUS plan were only just made public, Vice Admiral Mead said efforts to place Australians in overseas shipyards had already started.

"We're certainly working with the US and UK right now to embed people," Vice Admiral Mead said.

"We currently have sailors and officers undergoing nuclear reactor training in the US and UK right now."

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