To operate flying saucers from?
How would a base in Greenland make sense without a Sino-Soviet alliance in place?
To a Nazi-Sino alliance, it would be a boost!
Greenland is never going to be a significant base for anything due to the weather and the terrain.
Joking aside, Thule was a pretty significant air base with a deepwater harbour - allegedly the Northernmost in the World.
It was comparatively big, but only as a deployment base. Deploying and maintaining aircraft there must be a nightmare.