Vance's visit has thrust the remote Arctic base into the spotlight, as US President Donald Trump locks horns with Denmark over his public desire to annex Greenland from the Scandinavian country.

Located 1,524 kilometres (950 miles) from the North Pole, the base, named Thule Air Base until 2023, began life as a trading post founded by Greenlandic-Danish explorer Knud Rasmussen in 1910 next to a glacier.

It was then bought by the Danish state at the beginning of World War II before becoming an American weather station in 1946.

Following a defence agreement between the United States and Denmark signed on April 27, 1951 it was made into a military base between 1951 and 1953.

Greenland, which receives rent from the US administration, has been a party to this agreement since 2004.

The expansion of the station forced inhabitants of Pituffik, the local community, to leave their land for Qaanaaq, 140 kilometres to the north.

Their descendants have received apologies and reparations from Denmark, but their ancestral right to the rich hunting and fishing grounds has not been recognised.

- Protecting the United States -

Trump's administration argues the United States needs strategically placed Greenland, a self-governing Danish island, for security reasons.

"Vance refers to the importance of Greenland for US national security. That's true, it's been like that for a very long time," Marc Jacobsen, a researcher at the Royal Danish Defence College, told AFP.

The base's purpose is "to protect the US against threats, especially from Russia since the shortest distance from missiles from Russia towards the US goes via North Pole, via Greenland", according to Jacobsen.

The Pituffik base was used as a warning post for possible attacks from the Soviet Union during the Cold War and remains an essential part of the United States' missile defence infrastructure.

With its strategic location between North America and Europe the base still plays a surveillance role in the northern hemisphere.

At the height of the Cold War, more than 10,000 people were stationed at the base, most of them American, as well as fighter planes and bombers carrying atomic bombs.

In 1967, Denmark secretly authorised the United States to station nuclear weapons in Greenland. Officially, Copenhagen has refused to accept any nuclear weapons on Danish territory.

But on January 21, 1968, a B-52 plane carrying four hydrogen bombs crashed into the ice, revealing Denmark's dual nuclear policy.

Today, the base only houses around 150 US soldiers, alongside Danes and Greenlanders.

But it is not so much a question on the number of men as the quality of the equipment, according to Jacobsen.

"There are a very important radars there," he said.

The radars enable the detection of missiles and activation of counter-measures.

The military base, which also has a satellite control station, is operated by the 821st Space Base Group and is the only US military base on the Arctic island.

Its runway, some 3,000 metres (9850 feet) long, handles more than 3,000 American and international flights a year.

The base is also home to the world's most northerly deep-water port.

According to its website, this "provides a unique platform for arctic training, international scientific research and environmental programs".

Because of its location north of the Arctic Circle, Pituffik lives in constant darkness between November and February while the sun does not set from May to August.