The US-Japan "Fish Hook" SOSUS network. Map featured in the Ball and Tanter book The Tools of Owatatsumi (ANU Press, January 2015) Map 4, Page 54.
This continues Prasun K. Sengupta’s Undersea Webs article - the first part of which was republished as Part 1 - Undersea Webs - US-Japan SOSUS Against Soviets/Russia of May 29, 2016
Part 1 - Undersea Webs ended with the initial phase of the US-Japan SOSUS network which concentrated on tracking Soviet/Russian submarines entering and leaving Vladivostock-Sea of Japan. This limited network was permitted to rundown as the perceived threat from its initial Soviet/Russian target diminished in the 1990s.
Part 2 – Undersea Webs describes how in the early 2000s this limited SOSUS (+ with additional sensors eg. magnetic anomally) network was modernised and extended South (down through East China Sea, South China Sea/Philippine and Indonesian archipelagos through to the Indian Ocean) against the new Chinese Navy (PLAN) submarine threat. There were also key nodes at US naval bases at Okinawa, Guam and in Taiwan. The renewed threat from Russian subs and new threat from North Korean subs would also have driven the SOSUS+ expansion.
Part 2 – Undersea Webs
"However, in the early 2000s, facing an increasing PLAN submarine force and more aggressive PLAN submarine patrols, the USN decided that it needed a new chain of fixed arrays designed primarily to monitor the movement of PLAN submarines between the East China Sea and South China Sea on the one hand, and between the Pacific Ocean and the Indian Ocean on the other. Thus was born the US-Japan ‘Fish Hook Undersea Defense Line’ in early 2005 [see map above], stretching from Japan southwards to Southeast Asia, with key nodes at Okinawa, Guam and Taiwan.
Beginning from near Kagoshima in the southwest part of Kyushu, it runs down the Osumi archipelago to Okinawa, then to Miyako-jima and Yonaguni in the southern part of the Ryukyu Islands, past Taiwan to the Balabac Islands in The Philippines, to Lombok in the eastern part of the Indonesian archipelago, across the Sunda Strait between Java and Sumatra, and from northern Sumatra to the Andaman and Nicobar Islands. Three major gaps—between Yonaguni and Suao in north-east Taiwan (120km), between Kaohsiung in south-western Taiwan and the Dongsha (Pratas) Islands (450km) where the East China Sea meets the South China Sea, and across the Bashi Channel (220km) between Hengchun at Taiwan’s southernmost tip and Luzon Island in The Philippines—were plugged.
In addition, the USN installed a new SOSUS network, stretching from Sasebo down to Okinawa, in 2006, when the US cable-laying ship USNS Zeus [T-ARC-7] operated together with oceanographic survey vessels and nuclear submarines in this area. In July 2013, Beijing claimed that the US and Japan had jointly established ‘very large underwater monitoring systems’ at the northern and southern ends of Taiwan. One of these stretched from Yonaguni to the Senkaku Islands (about 150km), while the other covered the Bashi Channel down to The Philippines.
Thus, this US-Japan undersea trip-wire around the PLAN presently extends across the Tsushima Strait between Japan and the Korean Peninsula, and from Japan’s southern main island of Kyushu down past Taiwan to The Philippines. 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. Real-time information-sharing between the US and Japan joins the undersea defence line-up, effectively drawing a tight arc around Southeast Asia, from the Andaman Sea to Japan."