Securing the Digital Seabed

A Naval Strategy for Undersea Cable Protection

The Quad-Plus framework offers a maritime solution to China's gray zone warfare against critical communications infrastructure

By Claude Anthropic

The next conflict won't start with missiles flying—it'll be anchors dragging. This stark warning from defense analysts reflects a new reality in great power competition: the weaponization of merchant vessels against the undersea cables that carry 99 percent of global internet traffic and facilitate $10 trillion in daily financial transactions.

China's systematic campaign against undersea communications infrastructure represents a fundamental shift in gray zone warfare, one that demands an equally innovative naval response. The solution lies not in traditional fleet operations, but in a new model of maritime cooperation that leverages coast guard assets, advanced surveillance technologies, and allied integration to protect the digital lifelines of the modern world.

The Threat Below

Subsea cables have become the Achilles' heel of the digital age. These fiber-optic lifelines stretch across ocean floors, making them ideal targets for sabotage with minimal resources while providing plausible deniability for malicious actors. Recent incidents demonstrate the vulnerability: in early 2025, Chinese vessels severed cables connecting Taiwan to the outside world, while similar operations in the Baltic Sea targeted European communications networks.

The pattern is unmistakable. Chinese fishing vessels cut two cables serving Taiwan's Matsu Islands in February 2023, isolating 14,000 residents for six weeks. In January 2025, the Chinese-owned Shunxin39 switched off its identification signal while passing over a cable near Taiwan, severed it, and reappeared under a different flag—a textbook case of maritime deception.

Taiwan, connected by just 24 subsea cables, faces existential risk. In a crisis, China could covertly sever these links, leaving 23 million people digitally isolated before firing a single shot. This capability transforms undersea sabotage from an irritant into a strategic weapon capable of paralyzing an island nation's economy, military coordination, and emergency response capabilities.

Naval Lessons from the Baltic

NATO's response in the Baltic Sea provides a blueprint for Indo-Pacific operations. The alliance's "Baltic Sentry" mission, launched in January 2025, deploys frigates, maritime patrol aircraft, and naval drones in a coordinated surveillance network. At least 11 Baltic cables have suffered damage since October 2023, prompting this unprecedented mobilization of naval assets for infrastructure protection.

The Baltic Sentry model demonstrates the effectiveness of layered maritime surveillance. Naval radar and sonar systems, aerial reconnaissance from military and commercial drones, and integration of Automatic Identification System data with commercial satellite imagery create comprehensive maritime domain awareness. AI-powered tracking systems at NATO's new Maritime Centre for the Security of Critical Undersea Infrastructure enable reaction times "within a half an hour or an hour"—dramatically faster than the 17 hours one suspected sabotage vessel dragged its anchor in 2024.

Most significantly, the operation demonstrates how mine countermeasures vessels excel in this mission. German Navy Commander Marcus Fiene, commanding the coastal mine-hunting vessel FGS Datteln, emphasizes that MCMVs' underwater sensor capabilities make them ideal for cable monitoring. "We are the CCTVs of the seas," notes Commander Arjen Kockx of Standing NATO Mine Counter Measures Group 1. "Nothing will remain unseen in this area."

The Quad at Sea

The Quadrilateral Security Dialogue has moved beyond diplomatic forums to operational reality with the July 2025 launch of the first "Quad-at-Sea Ship Observer Mission." Officers from the Indian Coast Guard, Japan Coast Guard, U.S. Coast Guard, and Australian Border Force embarked aboard the USCGC Stratton, creating unprecedented multilateral cooperation in undersea cable protection.

This initiative reflects a fundamental insight: coast guard vessels are better suited for cable protection than traditional naval assets. Coast guards operate under different legal authorities, enabling boarding and inspection of suspect vessels in international waters where naval forces might face restrictions. Their law enforcement mission provides legitimacy for the constabulary operations essential to deterring cable sabotage.

The Australian-led Cable Connectivity and Resilience Centre exemplifies this approach, working with governments and industry across the Indo-Pacific to support effective cable development and management. Australia's "gold standard" in cable protection—robust legal, regulatory, and policy measures—demonstrates how maritime nations can adapt their frameworks to address emerging threats.

Expanding the Maritime Network

The logical evolution of Quad cooperation is a "Quad-Plus" framework incorporating South Korea and the Philippines through the Indo-Pacific Partnership for Maritime Domain Awareness. This expansion would create a comprehensive surveillance network leveraging each nation's unique capabilities:

• South Korea brings advanced shipbuilding capacity and technology integration
• The Philippines provides strategic geographic positioning across key sea lanes
• Japan contributes world-class maritime patrol aircraft and submarine detection capabilities
• Australia offers vast ocean monitoring experience and underwater warfare expertise
• India provides extensive Indian Ocean surveillance networks
• The United States supplies satellite intelligence and global coordination capabilities

Public-private partnerships enhance this framework. The Maritime Security Consortium demonstrates how allied-made technology can expand surveillance capabilities cost-effectively. Integration with commercial satellite operators and shipping companies creates a network that spans military, civilian, and commercial domains.

Fleet Requirements and Industrial Base

Protecting undersea cables requires dedicated maritime assets. Current global repair capacity is woefully inadequate: cable repairs average 40 days worldwide, with Southeast Asian repairs taking twice as long as North Atlantic operations. Of 62 major cable ships operating globally, only 19 focus on maintenance, and merely two are U.S.-flagged and operated.

The SHIPS for America Act addresses this capability gap through Section 403, establishing a Cable Security Fleet modeled on the Maritime Security Program. Two SubCom cable ships will join this fleet, receiving annual stipends in exchange for availability during crises. However, broader industrial base development is essential.

Japan's shipbuilding industry offers immediate solutions. Pooling Quad resources to establish an allied-controlled cable repair fleet would reduce dependence on Chinese-operated vessels while building indigenous capacity. The initiative requires full funding of the Cable Security Fleet and Jones Act reform to enable allied shipbuilders to expand U.S. subsea capacity.

Technology Integration and Satellite Backup

Advanced surveillance technologies transform cable protection from reactive to proactive. Autonomous underwater vehicles equipped with fiber-optic sensors can monitor cable integrity in real-time. Surface vessel tracking correlates suspicious behavior with cable disruptions, building legal cases for prosecution.

Satellite constellations provide partial redundancy, but cannot replace cables entirely. Taiwan plans 700 satellite receiver stations to maintain basic connectivity if cables fail, while developing constellations with Eutelsat OneWeb and Amazon's Kuiper. However, capacity limitations remain severe: Google's Grace Hopper cable transmits 350 terabits per second—300 times faster than Starlink's 1 terabit maximum.

SpaceX's near-monopoly on satellite launch infrastructure raises additional concerns given Elon Musk's business ties to China. Protecting subsea cables must remain the primary line of effort, with satellites serving as emergency backup rather than replacement infrastructure.

Legal Framework and Maritime Law

International maritime law must evolve to address deliberate cable sabotage. The 1884 Submarine Cable Convention provides historical precedent, but requires updating for modern threats. Article 113 of UNCLOS mandates domestic legislation criminalizing cable damage, yet enforcement remains problematic in international waters.

The October 2024 Joint Statement on Undersea Cable Security, endorsed by 17 nations, establishes principles for cable protection but lacks enforcement mechanisms. The United States should ratify UNCLOS and propose new provisions extending cable protections beyond 200-nautical-mile exclusive economic zones.

Quad partners must develop multilateral maritime protocols outlining fast, proportional responses to cable interference. These protocols should enable immediate vessel impoundment, crew detention, and sanctions against upstream owners when sabotage is suspected. Regular exercises simulating cable attacks will prepare forces for rapid response.

Operational Recommendations

Naval forces must adapt their missions to address undersea infrastructure protection:

Enhanced Maritime Domain Awareness: Deploy persistent surveillance assets in cable-dense areas, focusing on chokepoints where cables make landfall. Coordinate with commercial shipping to identify anomalous vessel behavior.

Coast Guard Integration: Expand cross-training between naval and coast guard forces. Coast guard vessels' law enforcement authorities make them ideal for cable protection missions, while naval assets provide defensive capabilities.

International Cooperation: Establish permanent liaison officers at partner nation maritime operations centers. Real-time information sharing enables rapid response to developing threats.

Technology Investment: Develop underwater sensor networks that detect cable tampering in real-time. Integrate these systems with surface surveillance to create comprehensive domain awareness.

Legal Preparation: Pre-position legal frameworks enabling rapid prosecution of cable saboteurs. Coordinate with international partners to ensure consistent responses across jurisdictions.

Strategic Implications

Undersea cable protection represents more than infrastructure defense—it's about maintaining the rules-based international order that underpins maritime commerce. China's cable sabotage operations test whether democracies will defend the systems that enable their prosperity and security.

The Quad-Plus framework offers a measured response that avoids escalation while demonstrating collective resolve. By emphasizing coast guard cooperation over naval confrontation, the initiative maintains its defensive character while building capabilities to deter future attacks.

Success requires viewing cable protection as a core naval mission, not an ancillary task. The sea services must integrate undersea infrastructure defense into their operational planning, training, and procurement decisions. The alternative is ceding control of the digital domain to adversaries who understand its strategic value.

Conclusion

The battle for the digital seabed has begun. China's systematic campaign against undersea cables represents a new form of warfare that targets the nervous system of the global economy. The United States and its allies possess the maritime capabilities to defend these critical systems, but only if they act decisively.

The Quad-Plus framework provides the foundation for an effective response. By combining allied maritime assets, advanced surveillance technologies, and international legal frameworks, democratic nations can protect the undersea cables that enable modern civilization. The question is not whether they have the capability to succeed, but whether they have the will to act before it's too late.

The next conflict may indeed begin with anchors dragging. Our response must ensure it ends with those anchors—and the vessels that deploy them—permanently deterred from threatening the digital lifelines that connect our world.

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SIDEBAR: The Legal Challenges of Cable Protection in International Waters

Navigating the complexities of maritime law enforcement beyond territorial seas

The enforcement of cable protection laws in international waters presents unprecedented legal and operational challenges that could reshape maritime jurisprudence and naval operations for decades to come.

Jurisdictional Complexity

Under current international law, flag state jurisdiction governs vessels operating beyond the 12-nautical-mile territorial limit. This creates a fundamental enforcement gap: while UNCLOS Article 113 requires states to criminalize cable damage, prosecution depends on the flag state's willingness to act. When Chinese-flagged vessels damage Taiwanese cables, Taiwan cannot exercise jurisdiction over the perpetrators.

The legal framework becomes even more complex when vessels operate under flags of convenience. The Hong Tai, suspected of cutting Taiwan's cables in February 2025, flew a Togolese flag but was crewed by Chinese nationals and owned by a Hong Kong company directed by a Chinese citizen. This multilayered ownership structure deliberately obscures legal accountability.

Universal Jurisdiction Expansion

Establishing universal jurisdiction for cable sabotage—similar to piracy, terrorism, and crimes against humanity—would revolutionize maritime law enforcement. Under this framework, any nation could prosecute cable saboteurs regardless of flag state, vessel ownership, or location of the crime.

However, this expansion carries significant implications:

Precedent Setting: Universal jurisdiction for infrastructure attacks could extend to cyberattacks, satellite interference, or other hybrid warfare activities, fundamentally altering the legal landscape of international conflict.

Enforcement Authority: Universal jurisdiction requires matching enforcement capabilities. Naval forces would need explicit authority to board, search, and detain foreign-flagged vessels suspected of cable crimes—a dramatic expansion of high seas law enforcement powers.

Diplomatic Consequences: Broad interpretation of universal jurisdiction could trigger retaliatory actions by authoritarian states, potentially criminalizing democratic nations' intelligence activities or military operations.

Evidence Standards and Attribution

Maritime courts require evidence meeting criminal standards, but cable sabotage often relies on circumstantial proof. Establishing legal causation between vessel movements and cable damage requires:

Technical Forensics: Underwater surveys, cable integrity analyses, and engineering assessments to prove deliberate versus accidental damage. This evidence collection can take weeks or months.

Digital Evidence: AIS tracking data, satellite imagery, and vessel communications logs. However, sophisticated actors can manipulate these systems, creating evidentiary challenges.

Chain of Custody: Preserving evidence integrity across multiple jurisdictions and time zones, particularly when initial response comes from coast guard or commercial vessels rather than law enforcement.

Coast Guard vs. Naval Authorities

The legal framework significantly affects operational planning. Coast guard vessels operate under law enforcement authorities that enable boarding and inspection of foreign vessels under specific circumstances:

Hot Pursuit: If a vessel commits a cable crime in territorial waters, pursuing forces can continue enforcement action into international waters.

Flag State Consent: Diplomatic agreements can authorize allied coast guards to board vessels flying partner nation flags.

Port State Control: Vessels entering allied ports after suspected cable crimes can be detained and searched regardless of flag state.

Naval vessels face greater restrictions under international law. Military boarding of foreign-flagged vessels in international waters typically requires:

• UN Security Council authorization
• Self-defense justification
• Explicit treaty provisions
• Flag state consent

Enforcement Mechanisms and Sanctions

Beyond criminal prosecution, new legal frameworks could establish administrative penalties that bypass traditional judicial processes:

Port Access Restrictions: Vessels and companies linked to cable sabotage could face automatic bans from allied ports, creating significant economic consequences.

Insurance and Financial Sanctions: Maritime insurance companies could be required to deny coverage for vessels with cable sabotage records, making commercial operations financially impossible.

Corporate Liability: Extending criminal responsibility to beneficial owners and operators, not just immediate flag states, would pierce the corporate veils that enable plausible deniability.

International Court Jurisdiction

Expanding International Court of Justice jurisdiction to cover cable sabotage could provide diplomatic resolution mechanisms while establishing binding legal precedents. However, major powers including the United States, China, and Russia have limited ICJ acceptance, reducing the court's practical authority.

The International Tribunal for the Law of the Sea offers an alternative venue, but its jurisdiction currently focuses on traditional maritime disputes rather than infrastructure attacks.

Implications for Naval Operations

These legal developments would fundamentally alter naval mission sets:

Expanded Law Enforcement: Naval forces might receive coast guard-style authorities for cable protection, blurring traditional distinctions between military and law enforcement operations.

Evidence Collection: Naval vessels would require enhanced digital forensics capabilities, legal officers, and evidence preservation systems—capabilities traditionally associated with law enforcement rather than military operations.

Interagency Coordination: Successful prosecutions would require unprecedented coordination between naval commands, justice departments, and international legal bodies.

Deterrence vs. Escalation: The line between legitimate law enforcement and military confrontation could blur, potentially escalating routine cable protection into international incidents.

Unintended Consequences

Aggressive cable protection enforcement could trigger unintended escalation:

Reciprocal Actions: Authoritarian states might criminalize allied cable repair operations, intelligence collection, or submarine activities near their infrastructure.

Lawfare Expansion: The precedent of universal jurisdiction for infrastructure attacks could be weaponized against democratic nations' legitimate intelligence and military activities.

Commercial Impact: Overly broad enforcement could disrupt legitimate maritime commerce, particularly in contested waters where commercial and military activities overlap.

Recommendations for Naval Leadership

The sea services must prepare for this evolving legal landscape:

1. Legal Training: Officers need enhanced education in maritime law, particularly regarding cable protection authorities and evidence preservation.
2. Operational Procedures: Develop standardized protocols for cable-related boardings, searches, and evidence collection that meet international legal standards.
3. Technology Investment: Invest in digital forensics capabilities and secure evidence storage systems for extended deployments.
4. Interagency Partnerships: Strengthen relationships with coast guard, justice department, and international legal experts to ensure seamless law enforcement coordination.
5. Diplomatic Engagement: Work with allies to develop common legal frameworks that maximize enforcement effectiveness while minimizing escalation risks.

The legal framework for cable protection will shape maritime operations for generations. Naval leaders must engage actively in its development to ensure the resulting authorities support mission success while maintaining international stability.

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Sources

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Multilateral maritime surveillance initiatives expand as China escalates gray zone attacks on Indo-Pacific communications infrastructure

The United States and its Indo-Pacific allies are rapidly expanding multilateral undersea cable protection initiatives as evidence mounts of systematic Chinese sabotage operations targeting critical communications infrastructure across the region.

Recent high-profile incidents point to a troubling pattern of deliberate subsea sabotage—acts made harder to trace as Russia and China deploy thousands of older, foreign-flagged vessels to obscure attribution, according to defense analysts tracking the emerging threat.

The urgency became clear in 2025 when multiple incidents involving Chinese-flagged vessels severing Taiwan's undersea cables raised alarm across the Indo-Pacific security community. In January, Taiwanese authorities investigated the Chinese-linked cargo vessel Shunxin39 suspected of cutting an international undersea cable off Taiwan's northern coast, followed by the February detention of the Chinese-crewed Hong Tai cargo ship suspected of damaging a cable connecting Taiwan to its outlying Penghu Islands.

NATO's Baltic Sentry Provides Indo-Pacific Blueprint

NATO launched its "Baltic Sentry" operation in January 2025 following suspected sabotage of undersea cables, deploying frigates, maritime patrol aircraft, and naval drones to monitor the Baltic Sea. The initiative provides a proven model for Indo-Pacific operations, defense experts say.

The Baltic Sentry mission consists of warships, AI-powered tracking systems, and F-35 stealth fighter jets, with reaction times reduced to "within a half an hour or an hour" compared to the 17 hours one suspected sabotage vessel dragged its anchor in 2024, according to NATO maritime commanders.

At least 11 Baltic cables have been damaged since October 2023, with the most recent being a fiber optic cable connecting Latvia and the Swedish island of Gotland, reported to have ruptured in January 2025.

Quad-Plus Framework Accelerates Operational Integration

The Quadrilateral Security Dialogue comprising Australia, India, Japan, and the United States has operationalized undersea cable protection through concrete initiatives. In July 2025, the four nations launched their first-ever "Quad-at-Sea Ship Observer Mission," with officers from each country embarking aboard the US Coast Guard Cutter Stratton to strengthen interoperability and maritime domain awareness.

Australia has established the Cable Connectivity and Resilience Centre as its contribution to the Quad Partnership for Cable Connectivity and Resilience, supporting infrastructure development and management of undersea telecommunications cables across the Indo-Pacific.

Research suggests expanding this framework into a "Quad-Plus" arrangement. Expanding cooperation to include capable partners like South Korea and the Philippines through the Indo-Pacific Partnership for Maritime Domain Awareness would enable a "Quad Plus" to better leverage each country's intelligence, surveillance, and reconnaissance capabilities.

Legislative Support Builds for Cable Security Fleet

Congressional legislation is advancing to support dedicated cable repair infrastructure. The SHIPS for America Act includes Section 403 establishing a Cable Security Fleet, with funding authorized through the Maritime Security Trust Fund.

Two SubCom cable ships are designated to serve in the US Cable Security Fleet, modeled after the Maritime Security Program with annual stipends for participating vessels. The program addresses critical capacity gaps in cable repair capabilities.

Current global cable repair capacity remains inadequate for emerging threats. Globally, cable repair times currently average 40 days, with repairs in Southeast Asia taking twice as long as those in the North Atlantic. Of the 62 major cable ships that operate worldwide, only nineteen are dedicated to cable maintenance, and only two are US-flagged and US-operated.

Taiwan Emerges as Primary Target

Taiwan has become the focal point of cable sabotage operations, with Taiwan currently connected via 24 subsea cables, and in a contingency, China could covertly sever them, leaving 23 million Taiwanese isolated from the rest of the world.

Between early 2023 and early 2025, multiple incidents of suspected undersea cable sabotage occurred around Taiwan, including Chinese vessels severing cables to the Matsu Islands in February 2023, the Shunxin-39 damaging cables near Keelung in January 2025, and the Hong Tai 58 damaging cables between Taiwan and Penghu in February 2025.

The frequency of incidents has prompted Taiwan to designate cable infrastructure as critical national assets. In 2024, Taiwan's Ministry of Digital Affairs designated 10 domestic submarine cables as critical infrastructure, ensuring heightened security measures and government oversight.

Technology Integration and Satellite Backup

The undersea cable protection strategy incorporates advanced surveillance technologies and satellite communications as backup systems. Public-private partnerships, such as the Maritime Security Consortium, can help the US and Southeast Asian partners expand the use of low-cost, allied-made technology to improve subsea cable monitoring.

Satellite constellation development provides partial redundancy. Taiwan is developing satellite constellations with Eutelsat OneWeb and Amazon's Kuiper, and plans to build more than 700 satellite receiver stations to ensure a basic level of internet connectivity even if cables are cut.

However, satellites cannot fully replace cable capacity. Google's three-year-old Grace Hopper cable can transmit up to 350 terabits per second, a 300-fold improvement over the latest V3 Starlink satellites with speeds maxed at 1 terabit per second.

International Legal Framework Development

The United States is pursuing enhanced international legal protections for undersea cables. In October 2024, 17 nations including the United States, Australia, and Japan endorsed a joint statement on undersea cable security, committing to resist "undue influence by a third country on suppliers and service providers" and follow "best practices for permitting and regulation".

The US should ratify and propose new provisions to the United Nations Convention on the Law of the Sea that extend subsea cable protections beyond countries' 200-nautical-mile exclusive economic zones, drawing from the 1884 Submarine Cable Convention.

Strategic Implications

Defense analysts warn that cable sabotage represents a new dimension in great power competition. Subsea sabotage marks a new era in gray zone warfare, and the United States and its partners have a narrow window to expose and confront this threat before it becomes the new normal.

The threat extends beyond the Indo-Pacific. Countries have come to rely on a network of cables and pipes under the sea for their energy and communications, supporting about US$9 trillion worth of trade per day. A coordinated attack on this network could undoubtedly have devastating consequences.

However, experts note the technical challenges involved in systematic sabotage. Deliberately snagging a pipeline with a dragging anchor in relatively shallow waters can cause a lot of damage, but it is fairly indiscriminate trick with a shelf life, since the damage can be repaired, and deniability becomes increasingly difficult.

The Quad-Plus framework represents a measured response that balances deterrence with diplomatic stability, offering a multilateral approach to protecting the digital infrastructure that underpins the modern global economy.

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Sources

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Undersea Cable Security: Quad-Plus Initiative Against Maritime Gray Zone Warfare | Claude | Claude

How the US should push the Quad-Plus to protect undersea cables - Breaking Defense