The Maritime Self-Defense Force and the U.S. Navy are jointly operating an undersea submarine detection system on the floor of the Pacific side of the Nansei Island chain, including Okinawa, as part of efforts to counter China’s rising maritime activities, sources said.
The latest model of the sound surveillance system, or SOSUS, allows Tokyo and Washington to detect Chinese submarines traveling from the East China Sea and Yellow Sea to the Pacific, sources in the Defense Ministry and the MSDF said Wednesday.
It is the first time that the existence of a listening system solely targeting China has been revealed.
As the system is “top secret in the Japan-U.S. security system,” the MSDF provides an outline of the U.S.-developed system only to a group of key figures in the Japanese government, including the prime minister and the defense minister.
A spokesman at the Maritime Staff Office declined comment when asked by a Kyodo News journalist about the system.
It was already known that Japan and the U.S. had set up an older version of the system in the seabed of the Tsugaru Strait in northeastern Japan and the Tsushima Strait in southwestern Japan for Soviet submarines during the Cold War.
According to the sources, the latest SOSUS involves two cables with extensive networks of hydrophones — one stretching from Okinawa to southern Kyushu and the other from Okinawa to off Taiwan.
Hydrophones and other equipment are installed every few dozen kilometers, they said.
MSDF and U.S. Navy personnel operate the system at the MSDF Oceanographic Observation in Okinawa, located at the U.S. Navy’s White Beach base in Uruma, Okinawa Prefecture. The two sides share all information collected through the system, the sources said.
Other details, such as when the system was deployed, were not available.
The latest SOSUS runs a separate system to monitor Russian submarine movements through a cable on the seabed between Aomori Prefecture and north of Hokkaido, according to the sources.
Military sources said China also ran an undersea system to monitor Japanese and U.S. submarines traveling in the East China Sea and Yellow Sea from naval bases and key port facilities in Qingdao and Shanghai.