Hawaii is sending more Marines to Australia this year as part of an annual rotational deployment intended to increase combat capability west of the international date line as a counter to China and while the Corps tries to keep a lid on COVID-19 cases.

The aviation combat element for Marine Rotational Force-Darwin 2021 includes approximately 450 Marines from Hawaii from a tilt-rotor MV-22 Osprey squadron, a detachment of UH-1Y Venom utility and AH-1Z Viper attack helicopters, and a detachment of RQ-21A Blackjack drones.

The Australian Department of Defence said about 2,200 Marines would arrive by June to take part in the 10th iteration of the interoperability training that’s held between April to October during the dry season in the Northern Territory.

As of April 15, 1,700 Marines had arrived for this year’s rotation, according to the Australian government.

Four Marines have tested positive for COVID-19 so far, Capt. Thomas deVries, a spokesman for Marine Rotational Force-Darwin, said in an email.

“(They) were recognized in quarantine and procedures put in place by Northern Territory Health had identified, re-tested and isolated the Marines for the safety of the community and our service members,” he said.

The Marines had received a negative COVID-19 test in the United States prior to deploying to Australia. All deployed U.S. service members will continue a mandatory 14-day quarantine period and obtain a documented negative test prior to exiting quarantine, the Marine Corps said.

CNN, citing data provided by the Marine Corps, reported earlier this month that nearly 40% of Marines were declining coronavirus vaccinations. The news outlet said the Marines were the first branch to disclose servicewide numbers on vaccine acceptance.

In March 2020 the U.S. and Australian governments decided to delay the year’s rotation due to coronavirus restrictions, but by June allowed a smaller contingent of about 1,200 Marines to participate. Hawaii sent a Blackjack drone detachment.

Interoperability got a boost in a scenario that focused on a small naval expeditionary force’s ability to rapidly deploy, integrate with foreign partners and coordinate airstrikes, the Marine Corps said.

Marines and the Australian Army worked with armed Australian Tiger reconnaissance helicopters and Marine Corps Blackjack drones to identify targets. Airstrikes were then coordinated with Air Force B-1B Lancer and B-2 Spirit stealth bombers.

Australia’s Defence Department said the force “has grown in size and complexity since the first rotation of 200 U.S. Marines through Darwin in 2012, through to reaching the milestone of 2,500 Marines in 2019.”

In 2019, Hawaii sent 10 Ospreys, four AH-1Z Vipers, three UH-1Y Venoms and 800 infantry Marines from the 3rd Battalion, 3rd Marine Regiment.

Adm. Phil Davidson, head of U.S. Indo-Pacific Command on Oahu, said in a statement submitted to the U.S. Senate Armed Services Committee at a hearing in March that Australia is a “critical ally, partner and leading contributor to international efforts promoting a free and open Indo-Pacific.”

Under its “Pacific Step-Up” policy, Australia is enhancing assistance and infrastructure investments in Fiji, Papua New Guinea and the Solomon Islands, Davidson said. The United States and Australia are concerned about China’s investment in South Pacific islands and the influence it brings.

The U.S., Australia, Japan and India are part of the Quadrilateral Security Dialogue, known simply as “the Quad,” a coalition “with a common platform of protecting freedom of navigation and promoting democratic values in the region,” according to the Congressional Research Service.

During the Pacific posture hearing in March, Davidson called it a “diamond of democracies.”

“I have great hope that our ministerial-level meetings with the Quad … will build into something much bigger for the sake of the globe,” he said.