A new contingent of US Marines are headed to Darwin in the eighth rotation of American troops training down under.

The ramp-up from 1700 Marines expected to arrive this year to 2500 will be the first time US troop numbers reach the full planned complement.

The Morrison government says the increased US military presence was the result of Australia's strong alliance and friendship with the US.

This year, the Marines will participate in multiple training activities with Australian troops, including a new humanitarian assistance and disaster response segment.

Aircraft deploying to Australia’s Northern Territory include 10 MV-22 Osprey tiltrotors, four AH-1Z Vipers and three UH-1Y Venom helicopters, a Marine spokesman said.

Aircraft deploying for the rotation include 10 MV-22 Osprey tiltrotors, four AH-1Z Vipers and three UH-1Y Venom helicopters, Marine spokesman 1st Lt. Colin Kennard said in an email.

The aircraft represent “the most capable Aviation Combat Element” sent to Darwin since the rotational deployments began in 2011, he said.

“These aircraft increase the training value for MRF-D activities and increase our ability to respond to contingencies within the Indo-Pacific region,” he said.

To facilitate operations for the U.S.A. helicopters, temporary airfield matting has been installed at RAAF base Darwin.

Marines, airmen and soldiers recently practiced seizing a small Japanese island in an exercise that honed skills some experts say may be necessary in a face-off against China.

This entire mission profile simulated the process of securing advanced footholds for follow-on forces to conduct further military operations with rapid redeployment.

It kicked off with a free-fall jump onto Japan’s Ie Jima Island for reconnaissance and surveillance before 1st Battalion, 4th Marines “conducted a 600-mile long-range raid” to seize an airfield on the island.

This kind of approach could be necessary should the U.S. need to face-off against China, said American defense and security analyst Paul Buchanan: “I don’t think it’s a coincidence that the Marines are engaging in these sorts of exercises because that’s exactly the combat environment that they’re most likely to find themselves in, at least in the near future,”

An endangered dugong found dead here is believed to be one of only three that had been confirmed in waters around the northern part of this southern island.

The bureau is monitoring the mammals, designated by the central government as a protected species, whose habitat could be affected by land reclamation work for the relocation of U.S. Marine Corps Air Station Futenma in Ginowan to the Henoko district of Nago, both in Okinawa Prefecture.

Okinawa is said to be the northernmost limit of the habitat of dugongs.

Environmentalists have argued that the relocation project would destroy their critical habitat and called for a halt to the land reclamation work.

US Colonel James Schnelle is stood down from his job of commanding the largest contingent of Marines ever to rotate through the Top End after being caught drink-driving, a Darwin court hears.

Colonel James Schnelle, 48, appeared in Darwin Local Court this morning, charged with medium-range drink-driving.

The court heard he failed a random breath test on Darwin's Mitchell Street in the early hours of a Sunday morning late last month.

No conviction was recorded, but the court heard Colonel Schnelle had been stood down from his job of commanding the largest contingent of Marines ever to rotate through the Top End.

Colonel Schnelle is the highest ranking US Marine in Darwin, and is a decorated commander with three service awards.

"This is a man of very high character, he has no convictions anywhere in the world and has contributed immensely to society," Colonel Schnelle's lawyer told the court. "The US Marines are going to deal with him very harshly." His lawyer said any conviction would affect any assignments or promotions he could hope to get in future.