US President Donald Trump has been touting ambitions to build a "Golden Dome" missile defence system since returning to office.
The proposal would involve a network of possibly hundreds of satellites and ground-based systems to detect, track and intercept incoming projectiles.
Still mostly a theoretical initiative, the initial plan was to create a defensive shield covering the entire United States to "protect our homeland," Mr Trump said.
Now the president says it is "vital" Greenland also has a Golden Dome, and the US should control the Danish territory to build it.
What is the Golden Dome?
As part of his renewed campaign to seize Greenland, Mr Trump had threatened to place tariffs on eight European nations or even use force to take the territory.
But he has abruptly scrapped those plans, instead announcing that a deal was in the works that satisfies his desire for a missile defence system in Greenland and access to critical minerals.
Details remain scant, but during a speech at the World Economic Forum in Davos hours earlier, Mr Trump was still arguing that the US needed to take "ownership" of the Arctic island in order to defend it.
The Golden Dome system was inspired, at least in part, by Israel's Iron Dome, which has provided land-based protection from missiles and rockets since 2011.
It is envisioned that the Golden Dome will have both ground and space-based capabilities that can identify and stop missiles at four major stages of a potential attack.
Malcolm Davis, senior analyst in defence capability at the Australian Strategic Policy Institute (ASPI), said the Golden Dome was designed to provide as much "leak proof" missile defence capability as possible.
"Against nuclear-armed ballistic missiles, and hypersonic weapons that could be launched by US adversaries, so Russia, China, North Korea," he told the ABC.
It was "virtually impossible" to have a leak proof defence, but the system could reduce the chances of nuclear warheads reaching the US, he said.
Mr Trump said he had allocated $US175 billion ($262 billion) for the program, aiming to have an operational system by the end of his term.
But some experts say the price tag and time-frame is unrealistic.
Todd Harrison of the American Enterprise Institute estimates it could cost about $US1 trillion over 20 years, rising to as much as $US3.6 trillion for a fully capable missile shield.
A report by the Center for Arms Control and Non-Proliferation noted in June last year that the program remained in its conceptual phase.
But the US Congress had begun allocating funds for research, studies and classified development tracks.
Is a Golden Dome needed in Greenland?
Intercontinental ballistic missiles or any nuclear attack aimed at the US would inevitably pass over the North Pole across Greenland.
"It's not about covering Greenland. It's about shooting down missiles before they reach the continental US," Dr Davis said.
The US already operates a radar system at its Pituffik Space Base in Greenland, which provides the military with extra warning of incoming threats.
There is also a comprehensive network of missile radars in the north of Canada and across Alaska operated by the North American Aerospace Defense Command (NORAD) — the bi-national Canada-US command.
Stephan Fruehling from the ANU's Strategic and Defence Studies Centre said Greenland was located to the north of the NORAD systems, so there was an argument for putting more radars in Greenland.
"It would push forward the air defence parameter for the North American continent, at least in regards to cruise missiles," he said.
Dr Davis said Greenland's location could also "make sense" to utilise the Golden Dome's space-based missile interceptor capability to shoot down missiles in the boost and mid-course phase.
The boost phase is the initial, engine-powered part of a ballistic missile's flight, lasting typically one to five minutes from launch.
"The problem, of course, is that practically speaking, you're never going to shoot down every missile," Dr Davis said.
"So the logical response by the Russians and the Chinese, if the Americans go ahead with Golden Dome, would be simply to dramatically increase their numbers of missiles and warheads."
Why seize Greenland to boost defence?
The current defence agreements between the US, Greenland, and Denmark give Washington considerable leeway to expand its military presence in the territory.
"There really isn't anything stopping Trump, under the current arrangements, if the US wanted to expand radars into that area," Professor Fruehling said.
"So the argument that you need sovereignty in order to do that doesn't really hold water."
In a post on his social media site, Mr Trump said he had agreed with the head of NATO on a "framework of a future deal" on Arctic security, including discussions on the Golden Dome.
The Associated Press reported that NATO members have discussed as part of a compromise with Mr Trump that Denmark and the alliance would work with the US to build more American military bases on Greenland.
The Pituffik base is the only US base currently in Greenland.
"Based on what I'm hearing coming out of Davos, the deal that's emerging suggests that the Americans would have pockets of sovereignty around key US bases that they would deploy, but Greenland itself would remain under Danish sovereignty," Dr Davis said.
Professor Fruehling was skeptical that anything resembling the full Golden Dome plan would eventuate in Greenland or even in the US.
"The Golden Dome is more of a political slogan than a program," he said.
Some space-based interceptors and radar action layers already existed and there were plans to modernise and expand on those systems.
"The US will continue to build out their missile defence capability," Professor Fruehling said.
"But it isn't an either or … It's not a situation where you can say a specific element is the Golden Dome."
