Many thanks to SWLing Post contributor Fred Waterer, who writes:
“The History Guy” (a terrific YouTube channel) talks about the technical marvel of uniting the four radio networks and soldiers overseas via shortwave at Christmas 1942 and 1943.
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High Frequency broadcasting is also used for propaganda. ‘Tokyo Rose’ was a US citizen stranded in Japan at the start of WW2 in the Pacific. https://youtu.be/YKuJvnKbbrA Her broadcasts competed with the Armed Forces Radio