All 2,200 US marines will need to do a do a COVID-19 test and be able to show a negative result before boarding the plane to Australia.

The Department of Defence says each marine will have to do a coronavirus test within 72 hours of their departure and show a negative result before boarding the plane to Australia.

After they touch down in the Northern Territory, the marines will have to do another COVID-19 test and then undertake 14 days of quarantine. Before leaving quarantine, each person will be tested again for COVID-19.

To accommodate the large group, the Marine Rotational Force — Darwin (MRF-D) unit has rented a secure facility outside the NT capital for most of the US arrivals to quarantine in.

The first two groups, however, will quarantine in isolated accommodation on an unnamed Australian Defence base.

The arrival of the 2021 cohort will be the 10th annual rotation of US marines in Darwin.

The Biden Administration will likely be "focussed on national securities," meaning Australia may have to make harder choices in the defence space, according to the Lowy Institute’s Richard McGregor.

“Trump was focussed on trade,” Mr McGregor told Sky News. “The Biden Administration might be much more focussed on national securities.

“That might mean harder choices for us in the defence space.”

Mr McGregor said this may mean the US would expect Australia to look at things including “intermediate range missiles” and the possible placement of “more Marines in Darwin”

“They might like us to do greater naval exercises in the South China Sea,” he said. “I think they’re going to expect us to step up as a strong ally.”

As tensions between the US and China continue to simmer, researchers say the Biden administration could put a strategic spotlight directly on the NT's capital, given its proximity to Asia.

"There will probably be a rotational agreement like what we see with the Marines and the Air Force, but with some US Navy warships," Mr Thomas-Noone told ABC Radio Darwin.

Professor John Blaxland, of ANU's Defence Studies Centre, said Darwin would "likely see considerable additional attention in the coming weeks and years".

He said with the new administration "likely to continue to apply pressure on China" and come looking to Australia for additional help, it may be the Top End city that answers the call.

"Darwin's going to be more on the crosshairs than it has been for some time now," Professor Blaxland said.

The US Marine Rotational Force Darwin 2020 has completed its ninth rotation in the NT.

The MRF-D has departed after undertaking a range of exercises, which strengthened cooperation and interoperability with the Australian Defence Force.

The 1100 US Marines arrived in a series of tranches and completed a mandatory 14-day quarantine, prior to starting their training; and, were tested for COVID-19 on entry to Australia and a second time prior to exiting quarantine.

One of the Marines tested positive for coronavirus while in quarantine.

Planning is underway for the next year's MRF-D, which will mark its 10-year anniversary.

At remote ranges in northern Australia this summer, US Marines and Australian troops trained to guide US bombers to targets on far-flung islands, illustrating the Corps’ increasing focus on a potential war in the Pacific.

In August, Marines flew RQ-21A Blackjack drones in Australia for the first time as part of the month-long Exercise Loobye.

During the exercise, US B-1 bombers from Guam and B-2s out of Diego Garcia flew as far as 4,000 miles to the Delamere, Bradshaw, and Mount Bundley training areas in northern Australia, simulating long-range precision strikes. The bombers were supported by tankers flying out of Okinawa.

RQ-21s flew over the ranges to gather information before and after the airstrikes.

“We’ve done an awful lot with the US Marine Corps,” Houston said. “They basically are the only nation that really gets a chance to routinely mount an exercise invasion of Australia, and that relationship … has served us incredibly well.”