Undersea cables have long been the invisible arteries of the global economy. In the early months of 2025 those arteries became a contested battlefield in the Taiwan Strait, exposing a new layer of confrontation that sits below the threshold of conventional war. This is not accidental damage. It is a strategic campaign aimed at the digital lifelines that underpin Taiwan’s economy, its military command and control, and its international ties.

The pattern is now unmistakable. In January a major trunk line, the Trans-Pacific Express, was severed off northern Taiwan after a vessel operating with an interrupted identity and with its automatic identification system turned off was observed in the area. Taiwanese authorities treated the break as almost certainly deliberate and pointed to the abnormal behavior of the ship as evidence of a planned operation.

Weeks later, Taiwan detained a Togolese-flagged cargo ship crewed by Chinese nationals after an undersea communications cable linking the Penghu Islands and Taiwan was damaged. Taipei said the vessel had been detected near the damaged cable days earlier and had ignored attempts at communications before the break was reported. Beijing dismissed charges of sabotage as politicization, calling such incidents routine maritime accidents. The competing narratives are part of the grey zone playbook: plausible deniability coupled with operational effect.

Those operational effects are real. Taiwan relies on a relatively small number of submarine cables for the vast majority of its external connectivity. Losing one or more high-capacity links rapidly forces traffic onto lower capacity routes, degrades financial transaction latency, complicates overseas military coordination, and strains emergency communications. Domestic repairs also take time because Taiwan depends on a handful of international cable-repair vessels and must coordinate complex salvage and splicing operations in challenging weather and contested seas.

Taipei has moved quickly to respond on multiple fronts. It has expanded maritime monitoring of suspect vessels, particularly those flying so called flags of convenience, and prepared legal and regulatory changes that raise penalties for damaging undersea infrastructure. These steps aim to increase the cost of interference and to shrink the space in which covert interference can hide behind claims of accident or misadventure. But lawmaking and patrols are only part of resilience. Rapid detection, international cooperation, and redundant architecture matter as well.

Strategically, the Taiwan Strait cable incidents illustrate several hard lessons. First, modern power projection does not require kinetic strikes from aircraft and missiles. A relatively low-cost maritime operation that severs cables can achieve disproportionate strategic effect - isolation, confusion and economic pain - while leaving room for denial and escalation control. Second, the maritime domain and the digital domain are increasingly fused. Control of the seabed and control of data flows are now mutually reinforcing elements of influence in crisis. Third, the campaign model favors actors who can leverage commercial shipping, obfuscate vessel identity, and exploit the slow, multinational logistics of cable repair.

Policy responses should therefore be layered. Tactical measures include round the clock mapping of cable routes, publicly accessible alerts for vessels operating near critical infrastructure, requirements that ships maintain AIS transponders in sensitive zones, and the listing and monitoring of repeat-suspect vessels that use flags of convenience. Operational measures should expand Taiwan’s capacity to detect tampering through seabed sensors and acoustic monitoring and to accelerate repair by securing agreements with commercial cable ship operators and reserve repair assets. Strategic measures must involve allies - because undersea cables are transnational assets, protecting them is a common interest - and include information sharing, coordinated naval and coast guard surveillance, and joint protocols for responding to suspected sabotage.

There are also corporate and legal dimensions. Private maritime registries, classification societies and ship insurers can play a role by enforcing transparency around ship ownership and operational intent. Telecom companies that own cables must be part of national continuity planning and should be incentivized to diversify landings, add interconnects, and harden landing facilities. International law and established norms for protecting submarine cables exist, but they were written in an era when most damage was accidental. The present environment calls for updated norms, reinforced monitoring and faster mechanisms for attribution when incidents occur.

Finally, deterrence will require a credible ability to attribute and respond. Attribution in the maritime environment is difficult but not impossible when AIS manipulations, vessel ownership trails, satellite imagery and seabed forensics are combined. Public attribution reduces the deniability that grey zone tactics rely upon. Responses can range from diplomatic protest and targeted sanctions to the seizure of vessels implicated in sabotage, along with coordinated moves to secure alternate communications paths. The goal is to make the expected costs of interference exceed its potential benefits.

The Taiwan Strait cable cuts are a warning shot. They show how the shaping of strategic advantage in the 21st century will often occur on the margins - in the seafloor, in the dark water between islands, in the minute it takes to switch a satellite route or splice a fiber. Policymakers in Taipei, and partners in Tokyo, Washington and beyond, need to treat undersea infrastructure as a core element of deterrence planning, not as an afterthought. Without layered defenses and multilateral cooperation, fragile digital lifelines will remain tempting targets for those who prefer effects without open war.

Protecting the cables will not prevent all forms of coercion. But by combining legal reform, maritime domain awareness, technical redundancy, allied cooperation and credible attribution, democracies can impose friction on a low-cost, high-impact tactic and reduce its strategic utility. The undersea domain is now part of the contest for influence in Asia. The response should be commensurate with the risk.