The AUKUS announcement has fuelled more speculation about possible expansion of the marines' presence in the Top End, which Defence Minister Peter Dutton has already said he would like to see.

In an interview with the ABC, the USA's Charges d'Affaires in Australia, Michael Goldman, said talks on the subject were ongoing.

Michael Shoebridge, the director of defence, strategy and national security at the Australian Strategic Policy Institute, said northern Australia was becoming another staging point for US personnel, logistics and resources in the Asia Pacific.

Under the 2011 agreement, marines will keep returning to Darwin each dry season for 25 years, ending in 2036. The USA Charges d'Affaires, said the deployments were "just a beginning rather than an end" of the US presence in Australia.

Defence strategist Paul Dibb has urged the upgrade of the RAAF’s Top End “bare bases”, saying the government’s $1.1bn investment in RAAF Base Tindal is a “clear sign of the deteriorating security environment”.

Professor Dibb, who sounded the alarm over the vulnerability of Australia’s north in a landmark 1986 review, also called on the government to consider the acquisition of land-based missiles, to give the nation a credible long-range strike capability.

“We need strike, with significant range. Not short-range. The days of just sitting offshore are gone,” the Australian National University scholar and former intelligence chief said.

US Studies Centre defence analyst Brendan Thomas-Noone said USAF B-52s were likely to be “rotated through” RAAF Tindal.

“It’s about trying to present more targets for China to account for,” he said. “If you are able to land these bombers in Australia, in the Indian Ocean, in other parts of Southeast Asia, up in Alaska, that is a lot of different places that China would have to track, if there was a conflict.

The upgrade of the Tindal base will include major runway extensions, fuel stockpiles and engineering to support Australia’s new Joint Strike Fighters, US Air Force B-52 strategic bombers and RAAF KC-30 air-to-air refuellers.

It wouldn’t be shocking if, in coming years, attack submarines from the U.S. Navy, Royal Navy and Royal Australian Navy all sailed from the same base just 2,500 miles from the Chinese fleet’s main haunt in the South China Sea.

Australia is moving to acquire nuclear-powered submarines while also expanding a naval base on its northern coast that could shorten the distance the boats might have to sail in order to reach a combat zone.

And now there are signs that American and British subs might join the Aussie boats. It wouldn’t be shocking if, in coming years, attack submarines from the U.S. Navy, Royal Navy and Royal Australian Navy all sailed from the same base just 2,500 miles from the Chinese fleet’s main haunt in the South China Sea.

The RAN already has a base in Darwin, but it’s a small one that at present accommodates just nine small patrol boats. The Australian defense ministry in 2019 launched a $200 million project aimed at expanding the Darwin base with additional fuel storage and another wharf so that it can support large surface vessels and submarines.

Britain’s nuclear-powered submarines are to use Australia as a base so that they can have a more persistent presence in the Indo-Pacific region under plans discussed by ministers.

Senior government sources said that the AUKUS pact could lead to the Royal Navy’s £1.4 billion Astute-class attack submarines undergoing deep maintenance in the region so they can stay deployed for longer rather than returning to the Faslane naval base in Scotland.

The plans would materialise once the Australians start building their own fleet of at least eight nuclear-powered submarines over the coming years with the help of the British and Americans.

The source said that the trilateral pact announced last week “opens up opportunities” for the UK, adding: “You’ve got another base … if you want to have more of a persistent presence you need access to maintenance.”

James Peddell, a former defence technology attaché in Washington with experience in submarine technology, said that a base in Australia could allow UK submarines with conventional weapons to have a permanent presence in the region, and also enable cost-sharing between the allies.

A former Australian assistant defense secretary says there might be more Marines in Australia in the wake of a new trilateral defense alliance.

AUKUS, which officials had been talking about for the past 18 months, is about much more than submarines, Babbage said.

“We are going to see larger U.S. forces coming, including U.S. Army forces and air power coming here on rotation,” he said. “It’s quite likely the Marine Corps presence could be scaled up.”

The U.S. Embassy in Canberra and the Australian Defence Department did not respond Friday to questions about the possible effect of the trilateral defense pact on the Marine rotations.