Interesting, clicked a bit further and found out that submarines use VLF communication, however it's one way only: "Submarines carry only a VLF reception aeria

Interesting, clicked a bit further and found out that submarines use VLF communication, however it's one way only: "Submarines carry only a VLF reception aerial and do not respond on such low frequencies, so a ground-to-submarine VLF broadcast is always a one-way broadcast, originating on the ground and received aboard the boat." https://en.m.wikipedia.org/wiki/Communication_with_submarines https://en.m.wikipedia.org/wiki/Communication_with_submarine...