Thule Air Base (U.S. Military photo)

For the first time ever, the Pentagon will try to shoot down an intercontinental-range missile Tuesday. The move is partly a response to North Korea, which has test-launched three missiles in the past three weeks. Its official news agency said Tuesday morning that dictator Kim Jong Un threatened, “to send a bigger gift package,” to the U.S.

A new Russian military base in the Arctic is also putting attention on the Pentagon’s northernmost base, located in Greenland, which was originally built as a buffer during the Cold War.

Thule Air Base, 750 miles into the Arctic Circle, is not easy to reach or maintain.

Thule Air Base (Airman Magazine / Flickr Creative Commons)

But the U.S. did just complete a significant upgrade for space and missile defense there, one of several early-warning systems getting upgraded worldwide, reports CBS News’ Jeff Glor who recently returned from a special tour of Thule.

With developments in North Korea and Russia coming daily, Thule is not just on top of the world. It’s on top of many American military minds.

On one of the most isolated pieces of land on earth, a base with no roads leading in, an island covered more than 80 percent in ice, the Air Force needs to stay constantly connected to the sky.

At the height of the Cold War, Thule Air Base was a vital part of U.S. strategy and symbolism. Now, as new chills settle in, CBS News was invited on base by Colonel Christopher Eagan, who took charge at Thule, part of Air Force Space Command, just last year.

“We have a unique access this far north that the Department of Defense does not have anywhere else,” Eagan said.

In training sessions, airmen and women learn to surveil the sky. They are always on alert for the worst case scenario: a missile fired from Asia.

Satellites offer first detection of launches, but radar is essential to track after that and no U.S. base sits farther north than Thule. It’s the halfway point between Washington and Moscow and the location of the 12th space warning squadron.

Thule’s $250 million radar just received a $40 million software upgrade–one of six early-warning systems like this around the world being improved. More than 3,500 antennas can see 3,000 miles into space.