Water is a poor medium for photons, but a great one for sound. That's why the US and other countries surveil the seas with linked arrays of underwater microphon

Water is a poor medium for photons, but a great one for sound. That's why the US and other countries surveil the seas with linked arrays of underwater microphones, i.e. the Integrated Undersea Surveillance System (IUSS). https://fas.org/irp/program/collect/iuss.htm https://fas.org/irp/program/collect/iuss.htm