One Marine was killed when an MV-22 Osprey from the 15th Marine Expeditionary Unit experience a hard-landing mishap while conducting training aboard Marine Corps Training Area – Bellows at approximately 11:40 a.m., Hawaii time.
Twenty-two Marines were aboard at the time, and all other 21 have been transported to local hospitals for assessment and treatment.
The Marines were conducting routine sustainment training at the time. The 15th MEU departed San Diego May 10 on a seven-month deployment to the Pacific Command and Central Command areas of operation.
The cause of the incident is under investigation.

Osprey are due in Darwin this year for the Talisman Sabre (TS15) Wargames.

The US is beefing up its military assets across Asia, with Australian bases soon to host some of its most formidable strategic weapons.

A US defence official said American B-1 bombers were bound for Australia as a deterrent to what they described as China's "destabilising effect" in the region.

The move is part of the Obama administration's plans to "assert freedom of navigation" in the South China Sea.

Assistant US defence secretary David Shear confirmed the move.

"We will be placing additional air force assets in Australia as well as B-1 bombers and surveillance aircraft," he said.

China's foreign ministry expressed "serious concern".

The US air force said the B-1 bomber was the back bone of its long-range bomber force

Mr Shear told a special congressional hearing on the South China Sea the deployment of air assets to Australia was in addition to the doubling of US marines bound for Darwin, leaving their current base in Japan. "We will be moving significant numbers of Marines to Hawaii, Guam and Australia," he said. "So we will have a very strong presence, very strong continued posture throughout the region to back our commitments to our allies, to protect and work with our partners and to continue ensuring peace and stability in the region.

Marine and Navy leaders are looking to engage with more partner nations in Southeast Asia, which could leave a portion of the Corps' land-based unit in Australia aboard ships, traveling around the region.

Lt. Gen. John Wissler, head of III Marine Expeditionary Force, discussed future plans for the Marine Rotational Force-Darwin, which deploys to Australia's Northern Territory each spring, during the Navy League's Sea-Air-Space conference in mid-April. In the years ahead, the Marines deployed with MRF-Darwin could spend some time at sea, he said.

Having Marines on ships would extend their reach far beyond Australia so they could "continue that engagement and partnership throughout Southeast Asia," Wissler said.

About 1,170 Marines arrived in Australia in mid-April to form the fourth iteration of MRF-Darwin, a six-month rotational deployment that fits into the military's broader plan to shift its focus to the Asia-Pacific region. The Marine Corps began sending company-sized rotations in 2011, and leaders plan to eventually build up to a 2,500-person Marine air-ground task force there.

Wissler said U.S. and Australian officials are working on the agreements to plus-up to MAGTF-level. How future sea-basing options will be worked into the unit's deployments are still in the planning phases, he said.

"That could be any sort of unit, task organized for the available Navy shipping and the mission, just executed from a sea-based platform," Wissler said.

Like the patrols the Japan-based 31st Marine Expeditionary Unit conducts in the region. Wissler said the Chief of Naval Operations Adm. Jon Greenert has stated that "he's committed to having second set ... of two 90-day patrols."

"[We will] introduce this second amphibious ready group," Wissler said.

In March, Greenert said the amphibious assault ship America — which has not yet formed an ARG — is a "prime candidate" to lead the blue-green team in and around Australia.

"They will go into Darwin ... and conduct on-load and off-load," Greenert said.

Wissler said the military-to-military partnerships in U.S. Pacific Command are expanding. He highlighted two recent Marine training events with partner militaries in Southeast Asia: Malaysia and the Philippines.

"Our numbers of engagements and execution of the PACOM U.S. Security Cooperation plan are continuing on the rise ... in the quality and the location and where we're going and where we're reaching out," he said.

sea-basing further confounds any local agency over the growing foreign military presence.

The dry season in the Northern Territory has begun and a new rotation of 1,150 US Marines is trickling into Darwin from all over the world. They make up the fourth six-month rotation since former Prime Minister Julia Gillard and US President Barack Obama struck a deal in 2011 as part of the US military's "pivot" to the Asia-Pacific region. The number of marines rotating through Darwin began at a few hundred and is set to gradually increase to 2,500 by 2017.

Four years in, few if any of the initial debates surrounding the agreement and its repercussions have been resolved. This is partially by design. The gradual build-up has been just one element of a careful campaign to acclimatise locals to the US presence that's also involved community-focused regulations and outreach programs.

Last December VICE talked at length with Justin Tutty of Basewatch, a small group with numerous concerns regarding the US military presence, and asked him for his read on local feelings.

"I think most people in Darwin don't realise it's an issue yet. There's been a really tight propaganda campaign around it. And people up here are pretty relaxed to begin with. And I guess the scale and the scope was talked down. The people who are worried are the people who are tuned into past experiences of sexual assaults and the social problems that come associated with other rotations and other visits."

The Marines will be stationed in Darwin for training for the six months of the Top End's dry season. They are the fourth rotation since former prime minister Julia Gillard and US president Barack Obama struck a deal in 2011 to gradually increase the number of US Marines rotating through Darwin to 2,500 troops by 2017. A small ceremony was held at Darwin Airport with America Galaxy C5 as aircraft carrying CH-53E Super Stallion helicopters from Guam in Central America touched down. "We're coming from all over the globe," Lieutenant Colonel Eric Dougherty of the US Marine Corp said. He described the rotation in which US Marines will live and train at the Australian Defence Force's Robertson Barracks as "unique". "Most places we go to a different country and have our own base there. We're operating inside the base," he said. "But here we're going to be living inside the barracks. "You guys have opened up your homes to us. We're living in your guest house." Lt Col Dougherty said the training opportunities in the Northern Territory were a big drawcard. "You have some world-class training facilities here," he said. "Bradshaw training area (south-west of Darwin) is three times the size of anything we have in the States. "The outback truly is out back, with vast wide open spaces. "There's things we can do here we cannot do back in the States."

The rotation follows speculation the growing US military presence in Darwin could cause tensions with China. Lt Col Dougherty would not comment on what impact another rotation of US Marines would have on relations with China. Last year for the first time Chinese soldiers trained on Australian soil with the Australian Army and US Marines, but Lt Col Dougherty said no training was planned with China on this rotation. He said the Marines were keen to start sporting teams, including trying their hand at rugby union.