https://en.wikipedia.org/wiki/LORAN
Before LORAN, used radio beacon navigation and star navigation (from Newton time), and good human navigator could achieve about 50km precision.
You could easy see signs of star navigation on good preserved old planes - they all have some sort of fully glass dome, or blister, to provide good near semi-sphere view. And sure, all those before-GPS era planes have separate navigator job position, sometimes shared with mechanic.
https://www.reddit.com/r/WWIIplanes/comments/59xfkz/pby_wais...
You could ask, how planes could fly with 50km precision? Answer is easy - at all plane routes built ground structures easy seen from air and last mile navigation become essentially visual flight, nothing more, nothing less.
On some places ground navigation structures preserved now, for examples:
https://en.wikipedia.org/wiki/Airway_beacon
https://en.wikipedia.org/wiki/Transcontinental_Airway_System