The NATO Science and Technology Organization’s Centre for Maritime Research and Experimentation has developed a standard for underwater acoustic communications called JANUS, which is recognised as a NATO standard by all NATO Allies since 24 March 2017. This marks the first time that a digital underwater communication protocol has been acknowledged at international level and opens the way to develop many exciting underwater communication applications.
I think this might become important to us. It is not just a military system.
Thanks to EagleSpeak for bringing this to my attention.
Chuck Hill's CG Blog 
Chuck,
It’s almost thirty years for me outside the telecommunication technology. However, I still understands its physics and limitations. On the bright side, it looks like they managed to develop a digital protocol and may be encryption for underwater communications, but the problem is that it is still acoustic and will continue to be. This means limited bandwidth and volume of information.
where can i get the more information about janus underwater communication