Modern SeaWeb (mostly underwater communications, detection and database) systems are no longer restricted to Cold War era seafloor wired together SOSUS sensors. As the diagrams below show - there is likely to be much greater use of multiple sensor (eg. LIDAR, infrared, magnetic anomally and sound) nodes that work to may platforms (submarines, UUVs, UAVs, USVs, surface ships, shore stations, patrol aircraft and satellites).
Nodes may be fixed seafloor, tethered, surface floating, many platform mobile, popping-up to send data bursts to satellite (eg. wavegliders) etc.
Underwater communications/relays between the nodes may be much more dependent on VLF-ELF radio waves or sound waves rather than cumbersome SOSUS cables.
All major naval powers have their research and installation programs. This continues with varying degrees of secrecy depending on national security culture. China and Russia maintain tight security while Japan or the US security may not be so tight (for reasons including commercial opportunities, organisational pride, and justifying taxpayer funding).
Discovered today is some interesting diagrams (below) from Japan's Ministry of Defense (MOD). Two from the Acquisitions, Technology and Logistics Agency (ATLA) http://www.mod.go.jp/trdi/saiyou/kenkyu.html.
Above is a Japanese SeaWeb concept diagram and description at http://www.mod.go.jp/trdi/saiyou/kenkyu.htmlas at March 13, 2016.
(Translation from Japanese by right-click mouse "Translate to English" and then by Pete)
Title Research of advanced underwater acoustic communication network technology (warships equipped Research Institute)
In comparison with strong radio wave linear propagation, a sound wave in the sea is refracted in accordance with the change in the water temperature and water pressure. Sound wave propagation follows a complex path. Thus in order to stretch a digital communication using sound waves in the sea, it is necessary to suppress the influence of multiple reflections bouncing off the sea surface and the seafloor.
Therefore, in this Japanese Defense Institute - to suppress the influence of multiple reflections, we conducted a study on advanced underwater acoustic digital communications that enables telecommunication.
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(Courtesy Japanese language document from Japan's MOD ATLA agency http://www.mod.go.jp/atla/ats2015/image/pdf/P12.pdf 2015 in connection with http://www.mod.go.jp/atla/ats2015/ )
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Above is a Japanese concept diagram from http://www.mod.go.jp/trdi/saiyou/kenkyu.html as at March 14, 2016.
(Translation from Japanese by right-click mouse "Translate to English" and then phrase order rearrangements by Pete)
Research of next-generation radar warning and control (electronic equipment Institute). We aim to further improve the performance of warning and control radar needed to respond in the future of stealth aircraft and ballistic missiles.
Unlike previous performance improvements, which were acheived by the size of the antenna, a distributed network of small antennas can be electronically configured to take account of the size of the attacking aircraft or missile. We are studying a distributed radar network to achieve what can be considered a large-scale radar equal to or higher than current detection performance.
Thus we shall apply the most advanced MIMO (Multi-Input Multi-Output) Radar techniques to achieve an equivalently large antenna optimally combining signals from a network of small antennas.
Pete's Comment - Presumably China and Russia are working on similar radar concepts as an air/missile defence priority as those countries have to face current Western stealth jets (F-35, F-22s and B-2s).
Pete