An ex-US Marine bomb technician set alight in a barbecue explosion is claiming officials knew about a gas leak which led to the incident.

The 25-year-old has claimed in court documents seen by the ABC that he received 30 per cent burns to his body after attempting to light a barbecue which officials knew had a gas leak.

The documents say that around 11pm on August 1, 2019, Mr Williamson had tried to light the barbecue "to cook some hot dogs and burgers", unaware there was a pre-existing leak.

Barrister for the US government, Dr Christopher Ward SC, argued that the US should "retain foreign sovereign immunity" in the case, as it did not involve any harm or incident to an Australian citizen.

Thousands of US Marines have arrived on our shores for a mission that is also bolstering the amphibious warfighting capability of the Australian Army.

The Marines – who arrived in the Northern Territory for their 12th annual rotation in March – specialise in amphibious operations and are also in the middle of a major transformation to match China’s armed forces.

Colonel Brendan Sullivan, the commanding officer of this year’s Marine rotational force, said this year’s training exercises in Australia and the surrounding region offered “incredible opportunities”.

Asked if they were seeking to replicate potential conflict scenarios in the South China Sea, the Pacific Islands or the Taiwan Strait, Colonel Sullivan said that was something “we’re grappling with right now” as the Marines sought to project force across a greater range.

“We’re going through a force design process where we’re trying to achieve the force that we think we’re going to need to have in the years ahead … and trying to get after some of the challenges that we think are associated in those operating environments,” he said.

“We’re trying to posture so that we can be ready to operate in that type of environment in the near future.”

This year’s Marine exercises include Predator’s Run in the Northern Territory and Melville Island, north of Darwin.

Ten Marine Corps MV-22B Ospreys have arrived in Australia’s Northern Territory as part of a 2,500-strong rotational force, the Marine Corps said Tuesday.

The Ospreys, from Marine Corps Base Hawaii’s Marine Medium Tiltrotor Squadron 363, are deployed to Royal Australian Air Force Base Darwin, according to a Marine Corps statement and information released Friday by the U.S. Department of Defense with photographs of the aircraft.

The tiltrotors, air crew and support personnel make up the air combat element of Marine Rotational Force — Darwin, which began its annual seven-month rotation last month.

The 12th contingent of the rotational force since 2012 will practice expeditionary operations, geographically distributed communications, non-combatant evacuation, embassy reinforcement, humanitarian assistance/disaster relief and rapid projection of combat power

The Northern Territory is poised to play a key role in Australia's future missile defences, according to a Top End MP, as the region prepares for an influx of soldiers and defence force spending.

The presence of the US Marines in Australia's Top End is also poised to grow in the years ahead, with the review recommending an increase to the annual rotation.

The report called for greater "engagement with the US on deterrence, including through joint exercises and patrols; and strengthening Australia's sovereign military and industrial capabilities".

Dr Coyne said this could play out through the arrival in the north of more US ships and fighter jets annually.

"There's a strong possibility that we'll see more often, more frequent US Navy ship visits," he said.

"Certainly we're most likely to see a greater rotational force of US air force craft through northern Australia."

Federal government MP Luke Gosling said the country's north would be prepared to play its part. "There's no doubt that the Northern Territory and the Top End will be part of the [nation's] missile story," he said. "Why? Because we're defending Australia, and obviously, you can get more range into the northern approaches to Australia from the Top End."

The latest rotation of US Marines has touched down in Darwin as they prepare to join Australian soldiers in training in “humanitarian assistance, security operations, and high-end live fire exercises”.

The 2500 member strong Marine Rotational Force-Darwin will spend the next seven months working closely with their Australian counterparts as well as other partner nations from around the region.

It comes on the back of last week’s announcement of the AUKUS nuclear submarine deal, and Deputy Prime Minister Richard Marles said the US continued to be Australia’s “most vital security partner”.

“Over the next six months, the Australian Defence Force and US Marine Corps will conduct a comprehensive range of training activities including humanitarian assistance, security operations, and high-end live fire exercises."