Subsea cables facilitate the flow of over 99 percent of global internet traffic and $10 trillion in daily financial transactions. They are the unseen arteries of intercontinental communication and commerce—the physical manifestation of the internet. And right now, they’re under attack, Breaking Defense reports.
While, on average, subsea cables suffer from accidental faults once every other day, 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. Nowhere is the threat of subsea sabotage more acute than around Taiwan.
In early 2023, Chinese vessels were blamed for cutting the only two cables connecting Taiwan’s Matsu Islands to Formosa, leaving 14,000 residents reliant on microwave radio transmission for six weeks.
China continues to refine its tactics to obscure attribution and evade accountability. In January, the Chinese-owned, Cameroonian-flagged cargo ship Shunxing 39 reportedlydamaged a subsea cable near Keelung, Taiwan. The vessel switched off its identification signal while passing over the cable, severed it, and reappeared as the Tanzanian-flagged Xingshun 39 — an apparent attempt to confuse attribution, according to widespread media reports and statements from the Taiwanese government.
Taiwan is currently connected via 24 subsea cables. In a contingency, China could covertly sever them, leaving 23 million Taiwanese isolated from the rest of the world.
Subsea sabotage has become a preferred weapon in China’s ‘gray zone’ arsenal: a series of deliberate provocations designed to test international tolerance and alter the status quo without triggering open conflict. And right now, there’s no global playbook to stop it. A US-led approach to the challenge should include three steps: monitor, respond, and build resilience.
First, Monitoring
We need better visibility on who’s doing what, where, and when. The US and its allies must increase multilateral monitoring of the South and East China Seas.
While the Quad conducted its first ever Quad-at-Sea Ship Observer Mission this month, 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 to track and deter ships operating under flags of convenience in the Indo-Pacific.
NATO’s ‘Baltic Sentry’—which deploys frigates, maritime patrol aircraft, and naval drones to monitor the Baltic Sea—offers a model for the Indo-Pacific. The Quad Plus’s efforts should be underpinned by a layered sensor network: naval radar and sonar systems, aerial surveillance from military and commercial drones, and the integration of Automatic Identification System data with commercial satellite imagery to improve maritime situational awareness.
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. And building on the Quad Partnership for Cable Connectivity and Resilience, and the Cable Connectivity and Resilience Centre, the Quad should develop a mechanism enabling its maritime working group to collaborate with ASEAN to address enforcement gaps in international law related to the intentional severing of subsea cables.
Second, Response
When sabotage is suspected, allied states must be prepared to act. Options include immediately impounding vessels, arresting crews, and sanctioning upstream owners.
A Quad Plus should establish multilateral maritime protocols that outline fast, proportional responses to deliberate cable interference, whether through law enforcement or coast guard actions, to reduce legal and operational ambiguity and impose real costs on perpetrators. And to improve their capacity to react quickly, a Quad Plus should conduct exercises that simulate subsea sabotage response scenarios to prepare forces for future incidents.
Maritime law should be strengthened as well. 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.
While Russia and China’s positions as permanent UN Security Council members may prevent fruitful action at the UN, the US should continue rallying support through organizations like the International Cable Protection Committee to develop shared norms and establish precedence.
Third, Resilience
Redundancy is key. Alternative technologies like proliferated Low-Earth Orbit (p-LEO) satellites offer a partial backup. 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, while p-LEOs offer critical advantages in flexibility and rapid deployment, they cannot replace cables in terms of bandwidth and cost-efficiency. 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.
SpaceX’s ‘de facto’ monopoly over satellite launch infrastructure raises more troubling questions regarding Taiwan’s continued connectivity in a crisis, especially given Elon Musk’s business ties to China. Therefore, protecting subsea cables should remain the primary line of effort of the United States and its allies.
To further improve redundancy, the United States and its partners should make tangible investments in subsea cable repair and maintenance capacity to reduce reliance on Chinese-operated vessels. Globally, cable repair times currently average 40 days, with repairs in Southeast Asia taking twice as long as those in the North Atlantic. And 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.
The Quad should pool resources to establish an allied-controlled cable repair fleet and leverage Japan’s shipbuilding industry to build new vessels as needed. For the United States, this means fully funding the Cable Security Fleet, passing provisions like Section 403 of the SHIPS Act, and reforming the Jones Act to enable allied shipbuilders to expand US subsea capacity.
But ultimately, this isn’t just about infrastructure—it’s about deterrence. 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.
That means enhancing maritime domain awareness, establishing clear rules for rapid and proportional responses, and investing in resilient cable infrastructure and repair capacity. Because the next conflict won’t start with missiles flying. It’ll be anchors dragging.
Ryan Claffey is a research assistant for the Indo-Pacific Security Program at the Center for a New American Security, specializing in East and Southeast Asia, US–China strategic competition, minilateralism, and maritime security.
