In 1951…The United States signed a
Defense of Greenland Agreement, which allowed NATO members to utilize Greenland for military operations, including the construction of bases and other installations.
Over the following decade, the United States built 3 military bases.
Two have since been abandoned.
The remaining base was called Thule Air Base. The base has been renamed to Pituffik Space Base, and it remains the U.S.' northmost military installation.
It is less than 1,000 miles from the North Pole.
https://www.slashgear.com/1402972/project-iceworm-cold-war-pentagon-secret-greenland-base/