China's SOSUS
There are many methods of tracking a large capital surface ship. The most often-mentioned ways are reconnaissance satellites, over-the-horizon (i.e. OTH) radars, and aerial reconnaissance by aircraft or UAVs. However, I would like to discuss the overlooked topic of underwater detection.
The technology is 49 years old. It would be silly to claim that China has not or cannot duplicate SOSUS in the waters off of China.
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SOSUS, an acronym for Sound Surveillance System, is a chain of underwater listening posts across the northern Atlantic Ocean near Greenland, Iceland and the United Kingdom — the GIUK gap. It was originally operated by the United States Navy for tracking Soviet submarines, which had to pass through the gap to attack targets further west. Other locations in the Atlantic and Pacific Ocean also had SOSUS stations. It was later supplemented by mobile assets such as the Surveillance Towed Array Sensor System (SURTASS), and became part of the Integrated Undersea Surveillance System (IUSS). Many other listening posts are still in operation around the world.
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First SOSUS sensors
SOSUS goes operational
In 1961, SOSUS tracked the USS George Washington (SSBN-598) from the United States to the United Kingdom. The next year SOSUS detected and tracked its first Soviet diesel submarine. Later that year the SOSUS test system in the Bahamas tracked a Soviet Foxtrot class submarine during the Cuban Missile Crisis. SOSUS was upgraded a number of times as submarines became quieter.
SOSUS systems consisted of bottom mounted hydrophone arrays connected by underwater cables to facilities ashore. The individual arrays were installed primarily on continental slopes and seamounts at locations optimized for undistorted long range acoustic propagation.
The combination of location within the ocean and the sensitivity of arrays allowed the system to detect acoustic power of less than a watt at ranges of several hundred kilometers."
China can build this:
Type 052C Aegis-class destroyer #171 Haikou
But not this???
A hydrophone