@Carlosa @Indos if you haven't got your copy already, you can get that book for free (legally), just click on the PDF link:
The Tools of Owatatsumi - ANU Press - ANU
It talks about that surveillance system in depth. I'm busy haven't got time to check it out.
Unforgiving geography indeed. The PLAN's nuke sub fleet is constrained, their exit point to the Pacific Ocean is only a small gap between the Philippines and Taiwan, which can easily be monitored by Japan+US (one of the reason the US won't let Taiwan fall into PRC hands too easily). Their exit point to the Indian Ocean is similarly constrained.
I'll add one more map to your list:
The PRC might want to modify its 10 dash lines again and turn it into an 11-dash-lines to protect their Sub base in Sanya
. Right now, the first dash line is nowhere near that Sub base which means that by default, VietNam's EEZ boundary goes right up to the mid point between Da Nang and Hainan Island, which is only 70 miles away from the Sanya submarine base.
So with approval from Viet Nam, the US/JMSDF can install sensors right up to 70 miles from the PLAN's Sanya submarine base, without infringing China's sovereignty/EEZ. This means that not only can the US/JMSDF monitor when the PLAN nuke sub enters the Pacific/Indian Ocean, they can monitor those subs just right outside the Sanya base exit.
Carlosa, you live in Da Nang, don't you want assistance from JMSDF+US to install sensors to safeguard your hometown from a tsunami? But who knows, the Viet military might have already allowed these "tsunami early warning" devices to be deployed.
The red part pretty much sums up what the PDF keyboard warriors has been saying here. But beneath the surface:
The US is still the master chess player in Asia.