The map is from page 54 “Map 4. The US ‘Fish Hook’ Undersea Defense Line” of Desmond Ball and Richard Tanter, The Tools of Owatatsumi Japan’s Ocean Surveillance and Coastal Defence Capabilities (2015, ANU Press) http://press-files.anu.edu.au/downloads/press/p309261/pdf/book.pdf?referer=444.
The map may depict past or current SeaWeb undersea array positions (eastern Asia - inner western Pacific sub-section).
Submarine Matters has focussed on the SeaWeb all platform sea surveillance system since May 2014. Also see October 2014 and May 2015. SeaWeb is not only about surveillance but a system that relies on a huge electronic database with most of the data stored in the US. The closest allies of the US can access and benefit from SeaWeb through a variety of means including installing hardware and software portions of submarine combat systems.
These “keys” are expensive but may well be worth it. It is important to the US that allies pay “rent” for the installation and maintenance of SeaWeb. The allies also add to the database in peace and war.
SeaWeb has many mobile and fixed platforms. Mobile include submarines and fixed include undersea arrays. The undersea arrays utilize several sensor technologies - not just the older term SOSUS which implies sonar-acoustic sensors only. Where the arrays may be historically and/or currently is part of the article below. The article is based around the work of two of Australia’s most resourceful academics, who published a more complete text earlier in 2015. See the article below.
Perhaps indicative of the importance of SeaWeb “Big Data” to the functioning of Australian submarines Australian Vice Admiral (retired) David Shackleton indicated in the Lowy Interpreter, February 16, 2016:
“Submarines are supported by intelligence before they deploy and continuously throughout their mission. Intelligence can come from a wide range of sources with different levels of importance, but often from highly sensitive sources that need to be protected and need special communications handling. Some elements of the combat system have to be certified to handle such sensitive information so that it can be integrated with its own onboard data, and some members of the crew need to have the appropriate access rights for its use.”
On April 18, 2015, Hamish McDonald published an excellent essay on the Saturday Paper . While the following is just a portion - here is the string for the whole article https://www.thesaturdaypaper.com.au/news/defence/2015/04/18/japan-and-us-enclose-chinese-coast-within-sensor-net/14293190401772#.VYfFVij5hhP :
"Japan and US enclose Chinese coast within sensor net
“The US and Japan have quietly cornered the Chinese navy with an undersea surveillance ring that is framing Australia’s defence policy.
…a new study by two Australian experts suggests it is the Chinese who are cornered. Desmond Ball, the Australian National University nuclear strategist and analyst of electronic spy craft, and Richard Tanter, of Melbourne University, an expert on North-East Asian security and nuclear issues, suggest Japan and the US have China’s forces surrounded by trip-wires.
Their book, TheTools of Owatatsumi, reported here for the first time, details the networks of undersea hydrophones and magnetic anomaly detectors that, combined with data collected by ground stations, patrol aircraft and satellites, make it virtually impossible for Chinese ships and submarines to break out into the wider ocean undetected. In effect, a line of sensors has been drawn in the sea.
The trip-wire around the Chinese navy extends across the Tsushima Strait between Japan and Korea, and from Japan’s southern main island of Kyushu down past Taiwan to the Philippines. When first revealed, in a little-noticed article by Taiwan military intelligence official Liao Wen-chung in 2005, it was described as a “Fish Hook Undersea Defence Line”.
Controversially, the curve of the hook stretches across the Java Sea from Kalimantan to Java, across the Sunda Strait between Java and Sumatra, and from the northern tip of Sumatra along the eastern side of India’s Andaman and Nicobar island chain. Unlike the northern stretches around Japan and Taiwan, these extensions into South-East Asia would be largely American installed and operated.
Indonesia and India, both historic adherents of non-alignment despite recent warming to the US in the face of rising Chinese power, would be loath to admit to allowing the Americans to wire up their nearby waters, and would be perhaps even more embarrassed to learn that it had been done without their permission or knowledge.
Ball himself is not sure whether these South-East Asian sections of the line consist of fixed acoustic surveillance arrays in the manner of the long northern sections from Tsushima down past the Philippines. “I would expect the more southern segments to have been fully surveyed and prepared for expeditious deployment of other elements of the integrated undersea surveillance system in contingent circumstances,” he told The Saturday Paper.
These include towed arrays trailing behind surface ships and small acoustic sensors that can be scattered across the seabed unobtrusively at short notice in a program called the Advanced Deployable System.
“Outward movement of the Chinese subs based at Hainan would be very closely monitored, whether they headed south or north,” Ball said.
Information sharing between the US and Japan joins the undersea defence line up, effectively drawing a tight arc around South-East Asia, from the Bay of Bengal to Japan. Chinese vessels, above or below water, can’t move in or out of this net without being spotted by their rivals.
It is with all this in mind that one might reconsider the purpose of the US-led Exercise Balikatan in the Philippines – and the presence of the RAAF’s AP-3C Orion. It is for fishing inside the net.
The undersea system has not gone unnoticed by the Chinese. Their surveillance ships have sailed close to the Japanese shore stations where data from the arrays is processed. In 2006, Japan arrested for espionage a naval petty officer at its Tsushima Island anti-submarine base. He had made eight trips to Shanghai and been compromised by a relationship with a hostess from a karaoke bar.
In July 2013, Chinese newspapers reported that Japan and the US had built “very large underwater monitoring systems” north and south of Taiwan, and that large numbers of hydrophones had been installed “in Chinese waters” close to Chinese submarine bases.
…“The underwater approaches to Japan are now guarded by the most advanced submarine detection system in the world,” Ball and Tanter write. In addition, the “Fish Hook” ensures that Chinese submarines are unable to move undetected from either the East China Sea or the South China Sea into the Pacific Ocean. “It suggests that even without recourse to the overwhelming US assets, Japan would be ascendant in any postulated submarine engagement with China,” they said...