For decades, U.S. policy has been characterized by “strategic ambiguity.” Washington intentionally avoids answering two questions:

• Would the United States definitely defend Taiwan militarily?
• Would Taiwan be supported if it declared formal independence?

The purpose is to discourage both a Chinese attack on Taiwan and a unilateral declaration of independence by Taiwan. By leaving its response uncertain, the United States seeks to deter actions by either side that could trigger a conflict. Successive administrations, both Republican and Democratic, have generally pursued four goals: preserve peace and stability in the Taiwan Strait, deter the use of force by China, support Taiwan’s ability to defend itself, and avoid unilateral changes to the status quo by either Beijing or Taipei.

American concern about Taiwan is driven by several factors:

• strategic location – Taiwan sits near major sea lanes and occupies a key position in the Western Pacific.
• democratic values – Taiwan has evolved into a vibrant democratic society. Many American policymakers see support for Taiwan as consistent with broader U.S. support for democratic partners.
• economic importance – Taiwan plays a critical role in global technology supply chains, especially through Taiwan Semiconductor Manufacturing Company (TSNC), the world’s leading advanced semiconductor manufacturer.

It is reminiscent of the 1900 policy of the United States: The China Open Door. The policy was focused on securing international agreement of equal opportunity for international trade and commerce in China, and respect for China’s administrative and territorial integrity. The articulation of the Open Door policy represented the growing American interest and involvement in East Asia at the turn of that century. Still seems to ring true today – ambiguity and all.

But what’s at stake for China? From Beijing’s perspective, the principal potential gain is political and strategic: completing national unification, strengthening regime legitimacy, and improving China’s position in the western Pacific. The principal risks are economic disruption, military losses, possible conflict with the United States and its allies, and the long-term challenge of governing a resistant Taiwanese population. As a result, many analysts believe Chinese leaders face a difficult calculation: the symbolic and strategic value of Taiwan is extraordinarily high, but the costs of achieving reunification by force could also be extraordinarily high and highly uncertain. The uncertainty itself, more than any single factor, is one reason why China has thus far relied primarily on military pressure, economic influence, and diplomatic efforts rather than launching an invasion.

Massive Economic Costs. This is arguably the greatest risk. China’s economy remains deeply connected to global trade, finance, and technology markets. An invasion could trigger international sanctions, restrictions on advanced technology imports, capital flight, reduced foreign investment and disruptions to maritime trade.

Military Casualties and Uncertainty. A cross-strait invasion would be among the most complex military operations attempted since the Normandy Landings because of rough seas in the Taiwan Strait, limited suitable landing beaches, dense urban areas, mountainous interior terrain, and a well prepared and trained defending military armed with advanced western nations military technology. Even if China ultimately prevailed, casualties could be very high and victory could take much longer than expected.

Even if you “win”, military conquest does not automatically produce political control. Taiwan has developed a distinct political identity over several decades. The majority of the people on Taiwan do not primarily identify as “Chinese.” Taiwanese is an identity they see as distinct from the people on mainline China. So, even after a successful invasion, China could face civil resistance, political unrest, security challenges, and long-term occupation costs. The postwar burden could persist for years or decades.

Although the United States maintains a policy of strategic ambiguity regarding Taiwan, Beijing cannot assume that Washington would remain uninvolved. An invasion could potentially draw in not just the United States, but also Japan, Korea, the Philippines, Australia – possibly even Vietnam, Indonesia, Malaysia, and Singapore. The latter three control the Malacca Strait, a major choke point for oil, commodities, and most commercial shipping. What would invading Taiwan do to China’s international standing?

What is clear is that “One China” has been a long-standing goal of China/PRC and the regime of Xi Jinping has staked his legacy on reunification. In Chinese political discourse, reunification is often portrayed not merely as a policy objective but as a historical mission. Success could become a defining achievement comparable to other major milestones in modern Chinese history.

There is a lot at stake.

A Final Thought for this series… for the moment

The U.S. position is that it recognizes the People’s Republic of China as the government of China, maintains unofficial but robust relations with Taiwan, opposes any attempt to change Taiwan’s status by force, supports Taiwan’s self-defense, and seeks a peaceful resolution of cross-strait differences without formally endorsing either Taiwanese independence or Chinese sovereignty over Taiwan.

Things are not “broke” so no need to fix it. Military action is certainly a quick way to break things:

One area in which China can not project the same power is over the Malacca Straits. 80% plus of China’s oil supply flows through these choke points as well as a huge amount of commercial shipping. It is China’s “Malacca Dilemma.” 

Malacca is just one choke point. There are others.

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.

Virginia Class Submarine

The role of naval vessels, aircraft, missiles, drones, and ground forces are likely more familiar to the average citizen than the role, use, and operation of submarines. While I enjoyed the Hunt for Red October, I wondered if the screen writers wanted the submarines to perform an Immelmann Loop or some other amazing maneuver from the world of aerobatics. If jet aircraft are the Lamborghinis, submarines are the Dodge Ramblers of the order of battle. Your options are left, right, up, down, forward, and occasionally reverse. And doing all this blindfolded. Sound, sound detection, and silence are critical success factors. 

The U.S. submarine fleet is all nuclear powered which gives each submarine the ability to operate for extended periods of time during which fuel/fuel oil is not the limiting factor for operations. There are 14 Ohio Class ballistic missile boats (submarines are referred to as boats, not ships); 4 Ohio class boats were converted to Tomahawk cruise missiles. Each boat is capable of carrying up to 154 Tomahawk cruise missiles. The fast-attack (SSN) fleet consists of 28 older Los Angeles class boats, 25 newer Virginia class boats, and 3 from the Seawolf class. The Virginia and Seawolf boats are similar in capabilities. If you are interested in submarines and their operations in the 21st century, take a moment to watch this video on the Virginia Class submarine.

Virginia Class Submarines. The PRC’s China Maritime Studies Institute released their assessment of the Virginia Class submarine and its capabilities and threats. The title of the assessment was: The Elusive “Deep-Sea Beast”: Analysis of the Performance of the Main Equipment of the U.S. Navy Virginia-Class Nuclear Attack Submarine. The Virgnia Class has their attention because these boats are designed for classic submarine offensive operations, but also anti-submarine missions, special forces operations, intelligence gathering, surveillance and reconnaissance missions, and more.

The boat has advanced active and passive sonar systems, internal and external design features which are next generation noise suppression including the propulsion system which no longer utilizes the traditional massive propeller. All of these advanced systems are supported by advanced real-time processing solutions integrated into their specific mission. There are more than 400 sensors targeting internal ship noise and vibration that compromise the overall noise profile emanating from the boat – the profile that could be detected by other submerged units.  The suite of active and passive sonar is greatly enhanced with acoustic signal processing to identify underwater sounds from biologics to marine life to other underwater vehicles – manned or unmanned.

What does all of that mean? The Virginia class boats are capable of operations in the South China Sea if needed.

Sea Mines

Because of the current situation in the Straits of Hormuz, the general public is aware that sea mines remain a potent threat in denial of access operations. China might be expected to mine lanes of expected naval operation, waters around contested shoals and islands, and similar operations. China has no shortage of vessels from which to seed the waters. The U.S.’s most stealth means of laying mines is the submarine force. The US retains the capability to lay mines from surface vessels and aircraft. During WW II, the extensive mining of Japanese straits, ports, and waterways was accomplished by low flying B-29 bombers. It should be noted surface and air mine laying operations assume domination of the attending air space.

Denial of access operations would be a way for China to keep foreign vessels out. But at the same time, it is a way for other nations to keep China “in” and deny the flow of merchant shipping which is the life blood of the Chinese economy. Such an action is probably a last step before the outbreak of hostilities.  When the U.S. and allies embargoed oil shipments to Japan, it was the first domino to fall leading to Pearl Harbor. 

A modern sea mine is a self-contained explosive device designed to destroy ships, submarines and other types of vessels. Mines deny enemy ships and submarines access to specific ocean areas or channelize the enemy into operating in certain particular areas. As such, mines provide low-cost battlespace shaping and force protection capabilities for the U.S. Navy. And you do not have to bump into one in order to detonate the mine. Mines can operate on proximity triggers (magnetic, acoustic, pressure and vibrational) that are supported by microprocessors, e.g. to listen for the distinct and specific sound of a vessel’s propulsion, and machinery through the water. 

U.S. submarines are capable of laying specialized autonomous naval mines. The Mark 67 SLMM is a covert, submarine-launched mobile mine designed for shallow waters, while the Mark 60 CAPTOR encapsulates a torpedo. The Mark 60 waits on the ocean floor and uses its processing circuits to detect enemy submarines. Rather than exploding, the mine launches the torpedo. There are other mines in the inventory, but they operate similarly.

Unmanned Underwater Vehicles (UUVs)

But the truly next-level capability is with unmanned underwater vehicles (UUVs). The extent of which these are currently deployed and their planned future – e.g., the DARPA Manta Ray Project – are the subject of next level undersea warfare. The UUVs will extend the base submarine’s sonar and weapons suite to areas either inaccessible (depth, danger, or incident avoidance, etc.) or prudently avoided. From the base submarine, there is a complete integration of sensor and communication systems, target motion analysis, tactical situational awareness, command and control decision tools, and launch control of all submarine payloads, including torpedoes, missiles, unmanned vehicles, and countermeasures.

I suspect it is the future of SCS operations.