A deceased family friend who was a former Eastern Airlines pilot who started out flying prop planes in the 1930s and ended flying 727's told me that often they would check their navigation at night in the prop days when they flew around storms by vectoring commercial AMs stations. He said between WSM, WLW, WWL and WSB you could always check your location in the Southeast. The early receivers were analog so an ID was comforting to the flight crew in a dark cockpit. Also commercial piloting if done correctly can be very boring. Call letters at radio stations were "important" to him then. Now with GPS are they still using VORs?According to a documentary I saw on the History Channel, the Japanese listened to one of the Hawaiian stations on their way to Pearl Harbor. I don't know if they had the loop to vector on the Zero but the some of the DC 3 photos I have seen had the loop.
