THE US military presence in the Territory is likely to be enhanced under President Donald Trump, Prime Minister Malcolm Turnbull confirmed yesterday.

Around 1250 US marines and 13 aircraft will be deployed to the Top End in April.

It will be the third and most complex rotation of US troops.

“We have a strong ally in Washington and the US’s continuing strong presence in our region, which President Trump has committed to, is of vital importance for all of us,” he said.

“I expect, based on discussions I’ve had with the US President, the US presence in the region will remain strong and is more likely to be enhanced. We’ve seen General (James) Mattis, the new Defence Secretary, has been travelling through the region providing very strong reassurance to America’s friends and allies in the region."

The US Marines are coming to Darwin. That’s the firm opinion of Australia’s Defence Force.

An ADF spokesman said the marine presence in Darwin would not change under the new administration of US President Donald Trump.

He said Australia and the US were now working on full implementation of a 25 year defence agreement between the two countries.

This year’s US Marine rotation, arriving in Darwin in April, is forecast to be the most complex Marine Air Ground Task Force deployed to Australia.

Around 1250 marines and up to 13 aircraft, including four MV-22 Ospreys, will create opportunities for more complex and sophisticated training activities.

Concerns about the deployment had been raised following Mr Trump’s election as US President and his comments that allies should contribute more financially towards a US military presence in their countries.

“No, there is no suggestion that the marine deployment to Darwin is up for review,” an ADF spokesman said.

“The size and composition of each marine rotation to Australia is mutually determined based on the nature of the training, planned regional engagement activities, other resource commitments and respective national priorities,” the ADF spokesman said. “As this is a 25 year agreement, it was important to reach a sustainable approach for both sides ... we continue to work closely with the US to refine infrastructure requirements and implementation plans to support MRF-D rotations into the future.”

A United States Defence build-up in the Northern Territory is being welcomed by local businesses and watched closely by wary northern neighbours, as some of the world's deadliest fighter aircraft arrive.

Defence analysts say the increasing presence of US Marines in the Top End is a clear sign the US is bolstering its military presence in the region, as a squadron of its sophisticated F-22 Raptors touched down near Katherine this weekend for three weeks of exercises with the Australian military.

That will soon be followed by the next rotation of US Marines and a large contingent of aircraft.

The Defence Department said it constituted the largest and longest rotation of fifth-generation aircraft to Australia to date.

Dr John Blaxland from the Australian National University's Strategic and Defence Studies Centre said it was clear "the US has a much more robust presence in Australia."

Dr Blaxland said while there was "a fair degree of assurance" the current arrangement with US troops in Darwin would remain, "in terms of the US posture in South East Asia and the region more broadly there's enormous uncertainty".

"Does this mean the US administration will take a more confrontational approach towards China, say, in the South China Sea?

"If that's the case that has potential to have significant consequences in the neighbourhood; there'll be considerable pressure on Australia to participate and to facilitate that engagement."

Chief Minister Michael Gunner said he would work hard to help local businesses seize the opportunity of Defence contracts over the coming years. "I'll be in Canberra, knocking on doors, I will be opening them, and sometimes as the Chief Minister I can open doors the private sector can't," Mr Gunner said.

The US Pacific Command says the US alliance with Australia remains strong and discussions are proceeding to send a full Marine Air-Ground Task Force of 2500 Marines to Darwin by 2020.

Major Rob Shuford, a spokesman for US Pacific Command, said: “No changes have been made to the planned rotations of Marines to Australia since the two leaders spoke.”

Major Shuford was referring to the angry exchange over the phone between US President Donald Trump and Australian Prime Minister Malcolm Turnbull about the “dumb deal” by the Obama administration to accept 1250 refugees held in offshore detention centres.

Trump’s tough rhetoric raised the prospect of a rift with Australia and sparked concerns over the future of US plans to expand its Marine presence in Darwin.

NT Chamber of Commerce acting CEO Brian O'Gallagher emphasised the importance of the US-Australia alliance to the Territory. "Hopefully this is just a hiccup and what we are seeing is nothing more than the newness of a leader who is trying to impress those people who voted him to the Presidency."

The crisis in US-Australian relations created by American President Donald Trump’s rant over a refugee deal with Australia has cast a shadow over the future of US plans to expand its Marine presence in Darwin.

Mr Trump’s threat to “study this dumb deal”, struck between Australian Prime Minister Malcolm Turnbull and the Obama Administration to take thousands of “illegal immigrants from Australia”, is a further warning that none of the previous agreements between Australia and America are safe from change.

Mr Trump has made no secret of the fact that he believes US allies should pay more to host American military contingents. A cost-sharing arrangement between the two nations was only struck in October after months of to-and-fro, despite former president Barack Obama’s enthusiasm for the deal. The agreement with the Obama administration would see the number of Marines stationed in the NT increase to 2500 by 2020.

Mr Trump’s apparent willingness to abandon promises made by his predecessor puts this on shaky ground.

The effects of any downsizing of the planned US Marine deployment would have a significant impact on a Territory economy. which is already suffering duress.

The NT is relying on an increased defence infrastructure spend, including a $2 billion investment as a direct result of the Marine rotation, to tide over the economy as the Inpex construction phase ends.

Chief Minister Michael Gunner said the deal as it stood would provide a “significant economic boost” to the Territory.

However, he emphasised that the Australian Government had already committed to spending billions on defence in the Territory.

“I strongly disagree with many of President Trump’s views, actions and decisions,” he said.

“However, the NT’s relationship with the US is a long and enduring one and goes beyond the views and actions of a single President or Chief Minister. It is crucial to gaining important economic investments, most notably through defence spending and the placement of US Marines.”

Member for Solomon Luke Gosling agreed saying he was confident the deal would stay.

“You cannot underestimate the value of this defence co-operation and constructive United States engagement in our region,” he said.

Mr Gunner said despite President Trump’s behaviour an invitation to visit the Territory still stands.