Marine Beacon / RDF interest / publication ?
The east, west, and gulf coasts....had very low freq, marine radio beacons, which transmitted morse ID signals. At sea, you would tune to the respective freq....and rotate the RDF loop / antenna, to obtain the proper bearing for the beacon antenna, on shore.
You then would have a line of position......and with several stations plotted, you had an "electronic fix."
Many variables at work here......and your equipment must be tested, calibrated, etc. You also...applied a "correction factor" if needed.
It was a method / tool to assist with navigation. I used the RDF beacon system in the early 1970s.
If you are in Baltimore.....check out the USCG lightship....."chesapeake"
She not only acted as a floating lighthouse, but also still has the VLF antenna system in place.
Mariners were cautioned to not "ride the RDF beacon" during foggy weather........or you had the potential of colliding with the lightship.
And at one time, I had the marine RDF booklet....that detailed each stations location, freq, beacon call, etc.
I would like to obtain a copy .... or be able to locate the PDF version.
The pubs that I locate online are too recent to have the stations from the 1940s, 1950s, 1960s, etc.
Take Care