I'd guess they use either aucustic communications with some encoding sheme[0], or some kind of VLF communication system with very low bit-rates. [0]: https://e

I'd guess they use either aucustic communications with some encoding sheme[0], or some kind of VLF communication system with very low bit-rates. [0]: https://en.wikipedia.org/wiki/Underwater_acoustic_communication https://en.wikipedia.org/wiki/Underwater_acoustic_communicat...