True enough. They set a bearing due south from the stern of the boat for a full twenty four hours before they estimated arrival at 90 N.
So the magnetic compasses were useless, the gyro compass only slightly less so, no way to shoot the stars, no LORAN.
The INS was absolutely key.
I'll try to rephrase my question to get the answer I had in mind.
Given all of the challenges to navigation, an INS system was installed in the boat, and a couple of North American guys came along for the ride to care for and feed it. This INS was originally developed for the Navaho cruise missile. What was the physical factor that made this INS most suitable for installation in Nautilus?