War Beneath the Sea

War Beneath the Sea

Why Undersea Cables Are the New Front in the U.S.–China Rivalry

After years of protracted negotiations, on December 11, 2001, China finally joined the World Trade Organization, better known by its famous acronym, the WTO. It marked the beginning of a new era for the global economy. According to World Bank data, between 2001 and 2007 China managed to quadruple its share of global exports, establishing itself within just a few years as the world’s second-largest economy, surpassed only by the United States. It was an age of deep economic and technological interdependence, of unshakable faith in globalization and its promises. Today’s landscape looks very different. Trump’s trade war, the return of protectionist strategies, and the growing unease toward the Chinese behemoth all signal a clear shift in direction. While much has already been written about the ongoing U.S.–China rivalry, what is less well known is that the two powers are also locked in a rather unconventional struggle—one taking place far below the surface: the battle for undersea cables.

Subsea cables are fiber-optic cables laid on the ocean floor that carry data from one corner of the planet to another which, needless to say, represent an extraordinarily sophisticated technology. High-speed internet, international phone calls, cloud services, and financial transactions—including the SWIFT system—all rely on this vast underwater network.

According to TeleGeography, by 2025 there will be 597 operational cable systems worldwide. That amounts to more than 1.4 million kilometers of fiber crisscrossing the globe, transmitting over ten billion dollars’ worth of financial transactions every single day. The geopolitical stakes are clear: global trade, finance, and defense systems—just to name a few—depend on these cables. It’s no surprise, then, that undersea cables have become a crucial front in the ongoing U.S.–China rivalry.

The main — and historically dominant— producers of undersea cables are the American company SubCom, Japan’s NEC Corporation, and France’s Alcatel Submarine Networks. In 2008, Huawei Submarine—a joint venture of the Chinese telecommunications giant Huawei—entered the market. Now known as HMN Technologies, it has become one of the industry’s leading players in just a few years. HMN Technologies’ rise fits squarely within China’s “Digital Silk Road,” a 2015 plan pouring billions into digital infrastructure to cement its status as a global tech powerhouse. China’s ambitions have, unsurprisingly, drawn Washington’s attention, prompting countermeasures. In early 2020, a consortium composed of China Telecom, China Mobile, China Unicom, Microsoft, and Orange planned to build a 12,000-mile cable known as SeaMeWe-6, stretching from Singapore to France. HMN Technologies (formerly Huawei Submarine) submitted a $500 million bid, backed by substantial state subsidies—roughly one-third less than the competing $750 million proposal from the U.S. firm SubCom. At that point, the U.S. government decided to step in. It offered $3.8 million in training grants to members of the consortium (including Djibouti Telecom and Sri Lanka Telecom) and threatened sanctions against HMN Tech. Meanwhile, U.S. ambassadors sent letters “warning” partners of potential security risks if they chose to work with the Chinese company.As a result, China Telecom and China Mobile withdrew, and SubCom eventually secured the contract.

China was quick to respond, triggering a series of tit-for-tat measures. Beijing’s first move was to obstruct the construction of cables backed by the West and its allies. A clear example came with Chinese interference in the Southeast Asia–Japan 2 project, led by Japan’s NEC. Beijing accused the company of trying to install surveillance equipment in the undersea network. Another of Beijing’s tactics involves sabotaging cables through what has come to be known as the “shadow fleet” — a network of ghost ships that carry out covert operations on behalf of the Chinese state.These vessels, disguised as fishing boats, dredgers, or cargo ships, sail under flags of convenience and are financed by shell companies whose real ownership is hard to trace. It’s a complex system that enables China to sabotage rival cables. At sea, shadow vessels switch off their transponders — which normally allow ships to be identified — before damaging the lines. Taiwan has been among the main targets of such attacks. One of the most recent incidents occurred in February 2025, when the Hongtai 58, a vessel from China’s shadow fleet, severed a cable linking Taiwan’s main island with the outlying Penghu Islands. The ship, sailing under a Togolese flag but crewed by Chinese nationals, had already attracted attention for its repeated name and flag changes. It’s also worth noting that, despite strong resistance from the West, China has managed to gain ground in the market — simply by turning its attention elsewhere. Beijing is now focusing on countries across Asia, Africa, and Latin America, where it can leverage its political and economic influence and outcompete Western suppliers with highly attractive pricing.

It’s important to view the undersea cable war in the broader context of “decoupling” — the slow but steady separation of two deeply intertwined economic and technological systems. The United States and China are now openly striving to build increasingly independent supply chains and tech ecosystems. As political scientists Henry Farrell and Abraham Newman (2019) remind us, economic and technological interdependence inevitably entails geopolitical risks. Interdependence, they argue, can be weaponized. Global finance, information networks, and supply chains tend to operate as hub-and-spoke systems, where a small number of “hubs” — the most industrially and economically advanced states — channel the majority of flows to the “spokes.” When a state controls or dominates a critical hub, it gains coercive leverage over those that depend on it. In the case of undersea cables, if the United States and its allies were to control most of the network, they could use that position to exert pressure on the states that rely on it.

Naturally, this strategy is not without its costs. Rather than a single, integrated global digital network, two parallel and competing systems are emerging — one led by the United States and its allies, the other by China. This widening divide is driving up costs and complexity for global tech firms, which must either build duplicate infrastructure across both systems or pick a side — risking the loss of market access to the other. Both blocs are deepening the fragmentation of the global digital landscape. It is, without doubt, a vicious cycle: as the decoupling between the two powers intensifies, the network fractures further — and each break, in turn, only hastens the next. As a result, what was once a single, interconnected digital space is giving way to two rival ecosystems. Ultimately, far removed from the optimism that followed China’s entry into the WTO, the world now finds itself drifting toward a new era of division, uncertainty, and fragmentation.

Translated by Iuliana Cindrea

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