OK, but what did, say, DC-7 transatlantic pilots use? A compass? And then VFR after they hit land?
Over open water, I believe they used dead reconing. We had a Lockheed Constelation in a museum I used to work with that had a "drift" system where they could look down at water to determine ground speed and drift angle. Also, it had a bubble window in the top for a sextant.
That and a full time navigator is all you need.
Well, I'm thinking they "shot the stars". Every see those little bubbles on the top of aircraft in WWII? Those were for checking the position of the stars to determine where you were. Of course that doesn't help when it's overcast so they used ADF or RDF. In the early days of the airlines before they set up VOR stations they actually had lights set up at intervals every few miles on the airline routes. Of course transatlantic routes would be radio direction and compass plus stars.