2,200 US Marines Darwin before June 2021: Live Firing.

 Australian Government owned ABC News, January 6, 2021 reports : 

The US Marine Rotational Force - Darwin (MRF-D) unit has rented a secure facility outside the Darwin, Northern Territory, Australia for most of the US arrivals to quarantine in before June 2021.

"The ability for 2021’s MRF-D to go ahead under challenging global circumstances, is a testament to the endurance and adaptability of the Australia-US Alliance," Australian Defence Minister Ms Linda Reynolds. who is a former Brigadier General, said.

US Marines live firing in Australia 2016. All the way to .50 cal M2s and Mk 19? auto Grenade Launchers towards the end! (This video here and above was not an ABC article)
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While in the Northern Territory, the US marines and the Australian Defence Force (ADF) will do training activities including security operations and high-end live-fire exercises [see above].

"COVID-19 permitting, the ADF and MRF-D will also train with partner countries throughout the year, including exercise Talisman Sabre," Ms Reynolds said

Exercise Talisman Saber is the largest bilateral combined training activity between the US and Australian militaries and is planned to run from June to August this year along the Queensland coast.

About 2,200 US marines will arrive in Darwin by June.(Supplied: Australian Department Of Defence)
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The arrival of the 2021 cohort will be the 10th annual rotation of US marines in Darwin.

MRF-D Commanding Officer US Marine Colonel David Banning described the alliance between the US and Australia as "outstanding".

"We are excited to commemorate the 10th anniversary with two highly capable and interoperable forces that advance our shared goals, demonstrate the strength and endurance of our alliance, and contribute to regional security," he said.”