The US Marine Corps is facing a $25 million law suit for failing to discipline a colonel over his lewd conduct in Darwin which included sending inappropriate text messages to a female Australian major and showing pornography to a male navy commander.

The law suit was initiated last week by a woman whose child was sexually abused by Colonel Daniel Hunter Wilson after he was transferred to a new command in the US without being disciplined over his Darwin behaviour.

Australian military officers could be asked to give evidence in support of the legal action relating to Wilson, 56, who last year was sentenced to 5½ years’ jail for sexually abusing the woman’s six-year-old daughter.

Wilson, a 36-year veteran of the marines, was posted to Darwin for six months in the sensitive role as liaison officer for the Marine Rotational Force in early 2016.

But just 10 days into the job he was removed and sent back to the US following complaints about his behaviour from local officers, especially his Australian counterpart.

“Had they (the Marine Corps) handled it properly he would never have been stuck back where he could assault my daughter.’

United States Force Posture Initiative in Australia has commissioned the construction of the first military project to be built in Australia by the US since World War II.

The four-spot helicopter parking apron and supporting facilities will be built at RAAF Base Darwin at a cost of more than A$30 million.

The contract is the first of many expected to be delivered under the United States Force Posture Initiative in Australia, in which Australia and the US will invest more than US$1.5 billion into existing defense infrastructure and facilities in the Northern Territory.

The scope of work includes four additional airfield-rated concrete, paved parking spots with asphalt shoulders; installation of four additional Type III fuel hydrant pits connected to existing fuel lines; and relocation of existing fuel isolation valve pits. Additional work includes the installation of airfield ground lighting, stormwater collection and treatment system, jet-blast deflectors and construction of an asphalt access drive.

The presence of more than 1500 US marines in Darwin should be welcomed and is a "really positive engagement", Defence Minister Marise Payne says.

Senator Payne made the comments after viewing a computer simulation exercise involving Australian and US forces in which bombs explode in Darwin's Cullen Bay and the troops respond during a visit to Robertson Barracks in the Top End.

The simulator can be used for mission rehearsal exercises for any scenario before going to an "operational or live firing environment", Australian Army's Major Max Williams told the minister.

The number of US marines in Darwin has been gradually increasing to 2500 since first being stationed in 2012.

There are 15 different joint training exercises planned over the next six months.

The meeting comes at a time of increased tension between China and both the US and Australia. The US withdrew an invitation to China to attend the Rim of the Pacific naval exercises this year and US Secretary of Defence James Mattis warned Beijing during a speech in Singapore last weekend of consequences over its aggression in the South China Sea.

THE Australia-US alliance has never been more important, Defence Minister Senator Marise Payne said during her Top End visit on Tuesday.

Senator Payne, who was in Darwin with top US and Australian military brass, said the presence of the US Marine task force in Darwin represented a significant opportunity.

Questioned on China’s island expansion in the South China Sea, Senator Payne said Australia has been very clear about its position.

“We have encouraged all claimants – and it is important to remember there are multiple claimants – to resolve those issues peacefully in accordance with international law and according to the rules based global order,” Senator Payne said.

“We demonstrate that by our engagements in terms of freedom of navigation and freedom of over flight.

“The United States demonstrates its position according to its own approach.

THE Aviation Combat Element of the 2018 Marine Rotational Force – Darwin has arrived in the Northern Territory as part of the seventh and largest rotation to date.

This year’s Aviation Combat Element comprises eight MV-22 Osprey tilt-rotor aircraft.

Deputy Commander Northern Command, Captain Bryan Parker, RAN, said the increase in Ospreys gave Australian and US forces the ability to conduct more complex and sophisticated training activities and exercises.

“During this year’s six month rotation, MRF-D and its Aviation Combat Element will develop an enhanced amphibious capability with the Australian Defence Force,” Captain Parker said.

The eight MV-22 Osprey tiltrotor aircraft are from Marine Medium Tiltrotor Squadron 268 (VMM-268), based at Marine Corps Air Station Kaneohe Bay in Hawaii.

The MV-22 Ospreys arrived at the Port of Darwin on a US cargo vessel.