Comment by notadev
12 hours ago
Back in my Navy days, we were taught HF is the less susceptible to jamming so is used for critical comms like these in serious situations. My ship performed in one exercise related to a doomsday scenario. We sat all day listening to an HR receiver until we heard these same messages, and we would then record the characters spoken. The message was repeated so we could make sure what we wrote was accurate. We never responded. Instead, we then repeated the same messages on an HF transmitter, presumably as part of some relay.
I, too, was in the navy and supervised this very exercise on a ship. The exercise simulates a doomsday scenario that presumes satellite comms are out after a nuclear strike. Ships and other stations retransmit the messages over HF in order to eventually reach nuclear-armed subs for assured second strike capability. HF, with its semi-BLOS (beyond line of sight) range, is used to form a global communications network without satellites. The range of course depends on how much signal bounces off the atmosphere, which is why many stations are needed for redundancy. The whole exercise is Top Secret.
Until someone decides the ionosphere needs to stop working for such relays. And there is only one way that I'm aware of to do that and that would be stupendously bad news.