Subsea Cables Are This Century’s Hidden Battleground
LYNN KUOK is Lee Kuan Yew Chair at the Brookings Institution.
A Russian-crewed ship suspected of cable sabotage, Tromso, Norway, January 2025Rogan Ward / Reuters
In 1893, a few decades after the first transatlantic cable was laid, Rudyard Kipling published a poem about the marvels of “The Deep-Sea Cables.” As communication became nearly instantaneous, Kipling heralded the connectivity that was previously unimaginable, writing, “Let us be one!”
Over a century later, telegraph lines have given way to fiber-optic cables, but their unifying promise has all but faded. The seabed has become an arena of great-power competition, sabotage, and surveillance. Fiber-optic data cables carry 99 percent of transoceanic digital traffic, including financial flows and government, diplomatic, and military communications. But as risks grow and trust erodes, global cabling is splintering into U.S.-led, Chinese-led, and nonaligned blocs, with routes and landings increasingly mirroring geopolitical alignment rather than commercial logic.
The vulnerabilities of critical subsea infrastructure are especially pronounced in Europe. The September 2022 Nord Stream pipeline explosions in the Baltic Sea drew global attention to these risks. Subsequent incidents in the Baltic, including damage investigators traced to a Chinese-linked vessel, showed how actors from one region can endanger infrastructure in another. Increased vessel and submarine activity along Atlantic and Baltic routes has also heightened concerns about undersea surveillance, as adversaries map and monitor critical cable routes.
Asia faces similar risks, even if they attract less attention. Taiwan reports seven to eight cable breaks annually, with most linked to China—part of Beijing’s broader coercive campaign against the island. In March, Beijing unveiled a deep-sea cable cutter that is reportedly compatible with uncrewed submersibles and capable of severing cables at depths of more than 13,000 feet—twice the operational depth of subsea communication systems. But even as incidents become more frequent and the capacity for interference grows, states have a hard time attributing cable cuts to particular actors and holding those ultimately responsible to account.
These dangers are compounded by an overlooked bureaucratic challenge: the use of legal and regulatory pressure to deny, delay, or complicate cable surveys, installation, and repairs. In the South China Sea, such tactics have helped China expand its de facto control over the seabed. Some companies are rerouting cables around disputed areas rather than contesting China’s claims.
Despite the growing importance of subsea cables, the laws and institutions governing them have not kept pace. The relevant provisions of the 1982 UN Convention on the Law of the Sea (UNCLOS) were drafted for an earlier era and build on the 1884 Convention for the Protection of Submarine Telegraph Cables, which was signed by the monarchs of Kipling’s time. Securing the world’s subsea arteries demands a comprehensive global architecture that links national and regional efforts with international ones and modernizes the legal and institutional regime.
The United States is uniquely positioned to lead this effort. Although it has challenged China’s attempts to dominate the waters of the South China Sea by conducting freedom of navigation operations, the United States has largely ceded the sea floor. If this neglect continues, Washington risks losing control not only of communications and energy lifelines beneath the waters but the balance of power above.
UNCLOS UNDER STRAIN
UNCLOS guarantees certain basic freedoms. A coastal state enjoys sovereignty in its 12-nautical-mile territorial sea. But beyond that limit, all states have the freedom to lay, maintain, and repair cables, including in exclusive economic zones and on continental shelves—the submerged extension of a country’s land territory. The convention explicitly protects the laying and maintenance of cables on continental shelves and stipulates that coastal states “may not impede” these activities, subject to “reasonable measures” for resource development and pollution control. Although the United States is not a party to UNCLOS, it treats the convention’s provisions on subsea cables as reflecting customary international law, and they serve as the authoritative codification of cable-related rules alongside the narrower 1884 Convention, which remains the formal treaty instrument for nonparties.
Domestic implementation of UNCLOS, however, does not always conform to the convention’s requirements. For example, although China ratified UNCLOS in 1996, its 1989 Provisions Governing the Laying of Submarine Cables and Pipelines directly contradict the convention by requiring foreign companies to secure consent for cable routes across its continental shelf, as well as for maintenance or repair.
The legal framework governing subsea cables also suffers from structural flaws. Countries often struggle to hold perpetrators to account for deliberate damage to subsea cables given jurisdictional limits in UNCLOS, weak flag state enforcement, and difficulties attributing incidents to actors.If incidents occur beyond the territorial waters of a coastal state, then only the country in which a suspected ship is registered—the flag state—has jurisdiction to investigate and prosecute any actors suspected of causing damage to cables. But many commercial vessels are registered in regimes that lack the will or the capacity to act. This was brought into sharp relief in October, when a Finnish court dismissed sabotage charges against the crew of the Eagle S, a Russian-linked tanker suspected of severing five critical Baltic cables, on jurisdictional grounds because the incident had occurred beyond Finland’s territorial waters. The vessel’s flag state, the Cook Islands, has not initiated any proceedings.
Even when the will and the capacity to prosecute exist, successful prosecution remains elusive. Attribution—linking damage to a particular vessel or crew—is often difficult, and holding the sponsoring state accountable is harder still since it requires proof that the act was carried out under the state’s instructions or that the state had control of the ship or crew.
Taiwan’s experience underscores how difficult attribution usually is. Despite stepped up monitoring in response to frequent cable damage, Taiwan secured its first successful prosecution only this summer, when a Chinese captain of a Togo-flagged vessel was jailed for three years after being found guilty of intentionally damaging undersea communication cables five nautical miles off Taiwan’s coast.
Workers installing an undersea cable in Amanzimtoti, South Africa, February 2023Rune Stoltz Bertinussen / Reuters
Experts are also divided over whether cable sabotage can be prosecuted as piracy, terrorism, or even as a use of force or an armed attack, which could provide alternative bases for legal action. Unmanned platforms, meanwhile, introduce an additional layer of complexity. It is unclear, for instance, whether they constitute “ships” and thus trigger flag-state obligations, and the absence of a crew further complicates the already tricky matter of attribution.
UNCLOS also has loopholes that countries can easily exploit. For instance, a coastal state’s jurisdiction over marine environmental protection in its exclusive economic zones allows it to require environmental impact assessments, which may indefinitely delay cable works. On the continental shelf, its right to take “reasonable measures” to protect resources can block, delay, or condition the laying, maintenance, and repair of cables. Because a single cable often crosses multiple maritime zones and jurisdictions, there are multiple opportunities for obstruction.
The mundane nature of this bureaucratic obstruction belies its far-reaching consequences. Chinese objections and permitting hurdles delayed the Southeast Asia–Japan Cable 2 by over a year before its launch in July; such challenges have also deterred other projects. Recent conversations in the region on subsea electricity interconnectors, which are critical to energy resilience and security, reveal that governments are choosing to avoid the South China Sea altogether rather than seeking China’s permission. The U.S.-linked systems, Apricot and Echo, were originally designed to cross the South China Sea but were reengineered to avoid it, adding both distance and cost amid concerns over permitting delays and the security risks associated with operating in China’s claimed maritime areas.
Remedies under UNCLOS, meanwhile, are often impracticable. Private cable owners must rely on their governments to act. But the state-to-state dispute settlement system under UNCLOS is slow, limited where carve-outs apply, and politically fraught. To date, no state has brought a case under UNCLOS solely over subsea cable interference.
Institutional gaps compound these problems. The International Cable Protection Committee, an industry association representing the world’s subsea cable owners and operators, focuses on technical recommendations for cable installation, protection, and maintenance. The UN International Telecommunication Union, a specialized agency for digital technologies responsible for setting technical standards, established an advisory body for submarine cable resilience in November 2024 with a two-year term. Neither institution has a mandate to investigate sabotage, attribute responsibility, impose consequences, or mediate state-to-state disputes or company-to-state disputes. Addressing legal and institutional gaps is not a legal nicety or bureaucratic exercise; for the United States and its partners, it is a strategic imperative.
PATCHWORK PROTECTIONS
Awareness of the vulnerabilities facing critical subsea infrastructure is growing, but national and regional responses vary widely in ambition and scope. In 2025, the U.S. Federal Communications Commission adopted stringent rules to secure landing sites—where subsea cables reach the shore—and restrict foreign adversaries from accessing them.The U.S. Congress also introduced bills, including the Undersea Cable Control Act, aimed at preventing foreign adversaries from acquiring items needed to build, maintain, or operate undersea cable projects, and the Taiwan Undersea Cable Resilience Initiative Act, which directs the U.S. government to work with Taiwan and partners to improve monitoring, rapid response, and coordination to strengthen the security of Taiwan’s undersea communications cables. Through the Quad’s Partnership for Cable Connectivity and Resilience, Washington is also working with allies and partners to align investment and security standards for trusted cable systems.
Europe’s response is most advanced at the regional level. The European Union has adopted an action plan setting out measures to prevent, deter, detect, and respond to acts against subsea cables, as well as to repair any damage. The plan promotes the use of Science Monitoring and Reliable Telecommunications (SMART) technology, which equips data cables with sensors, although take-up remains limited because of concerns that the sensors could infringe on sovereignty or be tapped. NATO has established a coordination cell and a maritime center dedicated to the security of undersea infrastructure, increased air and naval patrols in the North and Baltic Seas, and launched initiatives such as HEIST to detect cable damage and reroute data via satellites.
In Asia, regional cooperation on subsea cable security remains relatively nascent, although it is developing. Until recently, the Association of Southeast Asian Nations tended to view critical undersea infrastructure through an economic rather than a security lens. It issued guidelines to streamline repair permits and formed a working group to coordinate repairs and maintenance. But that approach began to change in October, when ASEAN defense ministers adopted principles for defense cooperation related to the protection of critical underwater infrastructure.
At the global level, momentum is growing around a joint statement on the security and resilience of undersea communication and data cables issued in New York during the 2024 UN General Assembly. Originally endorsed by 15 countries and the EU, the number of endorsing countries has since grown to over 30, including the full G-7 and all Nordic-Baltic states. Although nonbinding, these principles establish norms such as prioritizing “secure and verifiable” supply chains, which effectively excludes high-risk vendors, and promoting “route diversity” to reduce risks when communications and data cables are compromised.
Although these national, regional, and multilateral efforts are important, the world still lacks systems at the international level for continuous threat monitoring and intelligence sharing, as well as common protocols for joint investigations, attribution, and coordinated political responses. Growing geopolitical fragmentation makes it harder to close these gaps and costlier to leave them unaddressed. Regular multinational exercises to test crisis procedureswould strengthen deterrence, as would mechanisms to expedite permits and repairs—alongside fixes to the international legal and institutional regime.
A NEW SUBSEA ORDER
A comprehensive global architecture linking international law, institutions, and operations so that each reinforces the other would strengthen the rules-based subsea order. The United States would benefit most from such an architecture: its economy and security depend on extensive data networks, its allies rely heavily on data and electricity cables, and its adversaries exploit legal gaps. Although some strategists privately argue for preserving legal ambiguity so that the United States could respond in kind, that approach would normalize tit-for-tat retaliation and erode the global order that supports U.S. interests.
Realizing such an architecture would require sustained leadership to align national, regional, international, and private-sector efforts. Given its global reach, its alliance network, and its convening power, the United States is well placed to play an enabling role in building a more coherent seabed security architecture. Domestically, this would mean providing strategic direction on subsea cable security and resilience and treating subsea cables as strategic infrastructure, not merely commercial assets; aligning defense, diplomatic, commercial, and regulatory objectives; and coordinating across agencies. Externally, it would involve working with allies, partners, and industry to link national measures, regional frameworks, international initiatives, and private-sector operations into a more integrated system—even as the United States remains outside UNCLOS. Whether Washington chooses to exercise leadership will ultimately depend on political will.
At the operational level, this architecture would require closer coordination of joint patrols in critical subsea cable corridors, including the South China Sea and the Luzon Strait. It would also require greater consensus on procedures for cable repair, particularly with respect to expedited permits for emergency cable repairs, access for repair vessels, and coordination among authorities during incidents.
Because most international subsea cables are privately owned and operated, often through consortia that include telecommunications firms and cloud service providers, public-private partnerships are essential. Although no standing, security-focused public-private partnership exists specifically for subsea cables, governments could adapt models for strengthening the resilience of overland telecommunications and for reporting cyber incidents to establish shared systems for threat information, incident reporting, and emergency response. At present, anomalies are typically detected by operators internally and reported on an ad hoc and voluntary basis, with no common threshold for what constitutes suspicious activity, when authorities should be notified, or how information should be shared across borders. Clearer rules for information sharing of suspicious activity and network anomalies would enable earlier detection of interference or surveillance affecting subsea cable systems.
Public-private partnerships should also establish operator responsibilities more clearly by assigning explicit obligations to private companies or consortia that operate subsea cable systems. These responsibilities should include diversifying cable routes and landing points to reduce single points of failure and limit the impact of disruption, as well as establishing baseline security standards for cable landing stations to address vulnerabilities at these critical but relatively accessible nodes. Although landing stations are increasingly recognized as critical infrastructure, both their siting and their operations are typically regulated as commercial matters, with security responsibilities distributed across multiple authorities and baseline physical and cybersecurity standards varying widely in practice. Common baseline standards would help reduce exposure to interference and surveillance at these points of access.
NETWORK EFFECT
Progress toward a comprehensive global architecture will also depend on strengthening regional and cross-regional linkages. More advanced regional frameworks could serve as pathfinders that are later scaled or linked globally. A stronger ASEAN framework for the governance and resilience of subsea cables would support a free and open Indo-Pacific by providing political cover and collective leverage against excessive jurisdictional claims.
ASEAN could adapt elements of the EU’s regulatory system to develop its own rule book for cable governance and resilience. This could include more transparent permitting processes and clearer guidance governing fees, obligations, and cost allocation across jurisdictions, which would narrow national-level regulatory discretion, reduce arbitrary delays and obstruction, improve predictability for operators, make projects more commercially viable, and strengthen collective resilience against external regulatory pressure. An ASEAN-EU charter for cable governance and resilience could help blunt nationalist resistance that a purely intraregional, ASEAN initiative might face, while EU technical assistance and funding could incentivize participation and support implementation. ASEAN could also draw on models of security cooperation by establishing a center—or expanding the mandate of the Information Fusion Centre in Singapore—to share threat assessments, coordinate navies and coast guards, and develop common protocols to safeguard critical underwater infrastructure.
RULES FOR THE DEEP
Operational coordination and intraregional and interregional efforts will ultimately be limited, however, without addressing the shortcomings of the international legal regime. States should thus seek to clarify the rights and responsibilities of coastal states and flag states under UNCLOS and establish domestic laws and regulations that implement obligations under it to strengthen compliance and accountability. Among other things, such efforts should encourage stronger penalties for intentional cable damage, clarify that “ships” under UNCLOS include unmanned platforms so that flag-state obligations extend to them and to their remote operators, and require that unmanned vehicles register with a flag state and carry unique identifiers for traceability and the establishment of jurisdiction.
States could address legal ambiguities and gaps either through a UN General Assembly resolution, which is unlikely given the current geopolitical environment, or through an ad hoc conference outside the UN process that a coalition of like-minded states convened. Such a forum would allow participating states to clarify responsibilities and develop shared standards; it would also allow the United States to play a leading role despite its nonratification of UNCLOS. The conference would seek broad participation, including from underrepresented regions such as Africa, the Indian Ocean states, and Southeast Asia, which are increasingly important nodes in global cabling. Operators and insurers could be invited to participate. The conference should aim to produce a code that articulates responsible behavior for subsea cables that later feeds into UN deliberations.
Finally, to support these efforts, like-minded states should create an intergovernmental organization for the security of seabed infrastructure. Its core mandates would include impartial technical investigations of cable damage, which could help lift the veil to expose any responsible state, and setting and auditing standards through a “trusted cable” certification program, which would give members a common basis for denying market access to noncompliant systems. It could also mediate regulatory disputes through state-to-state and company-to-state mechanisms, which would facilitate timely, mutually acceptable agreements.
Drawing on lessons from export control regimes and technology standards bodies, the organization’s members should anticipate that U.S. adversaries, such as China and Russia, may respond by building parallel systems, contesting the body’s legitimacy, or pressuring third countries not to participate. They might also seek to join to dilute standards, obstruct decision-making from within, and slow investigations, which underscores the importance of conditional membership, transparency requirements, and institutional safeguards. Founding members could eventually open the organization to wider participation, but only on terms that reinforce rather than weaken its objectives.
“ON THE TIE-RIBS OF EARTH”
Progress on these many fronts would reduce the scope for sabotage, surveillance, and regulatory obstruction. Stronger operational coordination, investigation, attribution, and penalization would make sabotage and gray-zone activity harder to execute and evade, thereby strengthening deterrence. A system for information exchange, an intelligence-sharing network, and a trusted cable certification regime would reduce surveillance risks. Defining the limits of coastal states’ rights and boosting collective leverage could minimize regulatory roadblocks and the tendency to avoid contentious areas. A meaningful code of conduct would articulate the behaviors expected of responsible states.
Stronger legal and institutional frameworks are no panacea—states could still flout international law, as China and others have done. But the aim of these legal and institutional measures would be to alter the cost-benefit analysis by raising the political, economic, and reputational costs of hostile or noncompliant actions. A global architecture that links national, regional, and international efforts and modernizes laws and institutions is critical to safeguarding these lifelines and ensuring seabed access. Without this architecture, the subsea order on which all countries depend will weaken. For the United States, the stakes are especially high. A defining contest of this century will be fought and decided, as Kipling put it, “on the tie-ribs of earth.”
