Updated 8:47 AM EST, Fri, Mar 05, 2021

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China’s ‘Underwater Great Wall’ Defense Line in South China Sea Begins to Take Shape

Defense in depth

(Photo : PLAN) Desktop model of part of China's Underwater Great Wall in the South China Sea.

China has begun implementing Phase Three of its undersea defense system in the South China Sea called the "Underwater Great Wall" by deploying underwater sensors as part of an international marine survey program.

China has deployed its first eight made in China floating sensors in the South China Sea as part of "Argo," a collaborative partnership of over 30 nations to provide a seamless global array allowing any country to explore the ocean environment.

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Argo is a system for observing temperature, salinity and currents in the Earth's oceans and has been operational since the early 2000s. The real-time data it provides is used in climate and oceanographic research.

Some military analysts say China's participation in Argo is intended to enhance its scientific knowledge about the disputed waters, especially what's beneath the surface, since the Chinese sensors have both civilian and military uses.

China plans to have 20 operational sensors about a meter beneath the surface of the South China Sea. China's sensors can monitor the submarine environment up to a depth of two kilometers.

Data from the sensors is transmitted to the mainland using China's BeiDou Satellite Navigational System that also has numerous military uses. China's decision to use BeiDou and not the U.S. GPS to transmit data from its sensors also has military significance.

This August, Vice-Premier Zhang Gaoli approved the plan replacing all imported sensors with ones made in China and supported by BeiDou. Chinese scientists are also developing technologies to probe undersea depths down to six kilometers.

Military analyst Antony Wong Dong said these sensors could benefit the People's Liberation Army Navy (PLAN) indirectly since its submarines demand a large amount of real time data about water temperatures, pressure and currents, among others.

"The South China Sea is very big and China still has a lot of blind spots," said Wong. "The sea environment changes fast. It will be really dangerous to deploy submersibles if they don't monitor the waters closely."

Taken together, these new developments seem to confirm suspicions China has triggered Phase Three of its plan to build an Underwater Great Wall in the South China Sea.

A news story in this website last June exposed the existence of this Underwater Great Wall. It said this wall will consist of sensors, robot undersea vehicles, torpedoes and a manned "deep-sea space station" to further solidify Beijing's control over this hotly disputed area.

The Underwater Great Wall Project will be disguised as a scientific "natural resource development project" requiring an undersea base and a fleet of drone submarines, according to sources.

Analysts said this allegedly civilian project will form the basis for a future underwater military defense system designed to cement Chinese hegemony over the South China Sea while keeping the U.S. Navy at bay.

This underwater defense line will complete China's triad of control over the South China Sea. The first leg of this triad are the military outposts on reclaimed islands defended by HQ-9 surface-to-air missiles (SAM) and supersonic jet fighters such as the Shenyang J-11, a long range air superiority fighter.

The second leg will be an ADIZ or Air Defense Identification Zone that will effectively bar military and civilian aircraft from outside China entering the airspace above the South China Sea without China's permission.

The Underwater Great Wall, the third leg, is meant to counter the U.S. Navy's fleet of attack and ballistic missile submarines against which PLAN has no credible defense. Anti-submarine warfare is the greatest tactical weakness of the PLAN.

Also arousing suspicion is the proposed location of this "natural resources project." Its deep- sea space station will be built at a depth of 3,000 meters below the surface and will be manned by a full-time crew. No country has ever attempted to build a manned underwater base at these crushing depths.

Analysts said this underwater station might anchor the Underwater Great Wall.

"But we can't rule out it will carry some military functions," said Xu Liping, a senior researcher of Southeast Asia affairs at the Chinese Academy of Social Sciences.

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