China is noted for the system of walls and fortifications known as the Great Wall that stretches 13,000 miles across its historical northern borders as protection against various nomadic groups invading from the Eurasian Steppe. Modern day China may one day be equally known for the underwater version it has constructed and continues to expand on the seabed of on its eastern border, the South and East China Seas. And ostensibly for the same reason: to stop “nomadic” submarines invading from the Pacific Ocean.

The underwater “great wall” consists of advanced acoustic and non-acoustic sensor technologies that monitor underwater activities as well as surface transits. The technological foundation of China’s submarine listening network is built upon a combination of advanced passive sonar systems, underwater sensors, and sophisticated data analysis tools The inputs are integrated to a regional central command and control center that coordinates local maritime and naval responses in immediate action is deemed appropriate, but it also is used to populate large databases used to analyze movements, uncover patterns, and possibly detect new operations and technology.

The purpose is part of its evolving anti-submarine warfare (ASW) capability, but it also supports China’s broader objectives of asserting its claims in the South China Sea for fishing, commerce, and territorial claims. The information gathered through this network enables Chinese naval forces to conduct more informed “grey zone” operations, ensuring that they can protect vital shipping lanes and respond to challenges posed by other regional powers. In this context, seabed listening is not merely a defensive measure; it is an integral part of China’s strategy to project power and influence across the maritime domain.

In addition to traditional passive sonar systems, China has invested heavily in developing underwater drones and autonomous vehicles equipped with advanced sensors. These platforms enhance the network’s reach and capabilities, allowing for more extensive monitoring of vast maritime areas without taking on additional infrastructure costs associated with installation and maintenance. The drones also allow exploration of places where the seabed depth offers substantial challenges.

Like all nations and industry, the Chinese have invested heavily in artificial intelligence and machine learning to enable more efficient data processing and analysis, allowing Chinese analysts to quickly interpret complex acoustic data and identify potential threats.

Despite its advancements, China’s submarine listening network faces several challenges and limitations that could impact its effectiveness. One significant challenge is the vastness of the maritime domain that needs to be monitored. While technological advancements have improved detection capabilities, there are still limitations regarding range and accuracy, particularly in deep-water environments where submarines have traditionally operated undetected. Additionally, the placement of sensors is dependent on “hardwire” connections which can be disrupted, tapped, or otherwise disturbed. This particular “arms races” will be waged in the arenas of technology, signal processing, AI analysis support, and new acoustic measures and counter-measures. The “underwater wall” as vast as it is presents challenges as components wear out or are compromised with zero-day intrusions.

Outside territorial waters, China has two underwater sensor arrays situated between the United States island of Guam and the South China Sea. Though officially for scientific research, the undersea listening devices are likely doing double duty, monitoring the movements of American and other foreign submarines and potentially intercepting and water-borne communications. This shows China’s commitment to expanding the range of early detection of potential threats. One array is near Guam and the other is located near Yap – a pathway that happens to lie along potential naval tracks leading from Guam to the South China Sea entrance south of the Philippines.

China’s submarine listening network constitutes a fundamental element of its defense infrastructure, directly supporting its expanding maritime objectives. This surveillance system enhances China’s awareness of underwater activities in the Asia-Pacific region while functioning as a strategic deterrent. The comprehensive array of acoustic sensors and monitoring equipment positioned along coastal areas and key maritime zones demonstrates the critical importance of subsurface intelligence gathering in contemporary naval operations.

The network serves broader strategic purposes beyond surveillance capabilities, reflecting China’s aspirations toward maritime dominance. Through substantial investments in sophisticated acoustic detection technologies, China seeks to safeguard vital sea lanes, reinforce territorial claims, and protect naval assets. In the context of increasing tensions throughout the South China Sea region, this submarine detection infrastructure significantly influences regional security dynamics and military strategic planning.