Chinese research vessels spend more time loitering near undersea cables in the Pacific Ocean than ships from any other nation, according to a new analysis by the Center for Strategic and International Studies. The Washington-based think tank compared the behavior of 200 research vessels from 47 countries, including the U.S. and Russia.

What You Need to Know

Undersea cables carry the overwhelming majority of global internet traffic, making them a strategic chokepoint for both commerce and military communication. Civilian research vessels operate under flags that grant them legal access to international waters, which complicates efforts to monitor or restrict their movements. The CSIS findings arrive as multiple authoritarian states, including Russia and Iran, have escalated activity around the same infrastructure.

How the CSIS Analysis Measured the Gap

The report found that Chinese vessels spent a "statistically significant larger share of time" near critical undersea infrastructure than their counterparts from other nations. That phrasing matters because it signals the pattern is not random noise from normal maritime traffic.

The Center for Strategic and International Studies examined vessel behavior across a global fleet, not a narrow sample. Researchers tracked how long ships lingered near cable routes rather than simply counting transits.

One documented case involved a ship from the Xiang Yang Hong research fleet. Between July and October 2024, that vessel spent time near three undersea cables linking the U.S. with Australia, Indonesia, Singapore and Guam.

The Lawnmower Pattern and Its Military Utility

Chinese ships moved in a "lawnmower" pattern, a back-and-forth grid that survey vessels use to build accurate seafloor maps. The technique is standard for legitimate oceanographic work.

That dual-use character is precisely what makes the activity hard to counter. The vessels are not part of the People's Liberation Army Navy, so they operate outside the legal framework that governs warship movements.

Civilian research hulls offer states a layer of plausible deniability. The data they collect, however, could support terrain analysis for sabotage or submarine operations in a future conflict.

  • Dual-use cover: Civilian research vessels can gather military-relevant data without triggering the legal restrictions that apply to naval ships.
  • Seafloor mapping: Lawnmower survey patterns produce detailed terrain models useful for submarine navigation and cable targeting.
  • Plausible deniability: Governments can deny intent because the ships carry no military designation.
  • Persistent presence: Repeated visits over months build a comprehensive picture that single transits cannot.

A Broader Pattern of Infrastructure Probing

The Chinese activity fits a wider trend of authoritarian states pressing against undersea infrastructure. The Telegraph reported 500 incidents of Russian monitoring near undersea cables over the past five years, involving 17 Russian trawlers mapping links between the U.S. and Europe.

Iran has gone further in its rhetoric. An Islamic Revolutionary Guard Corps spokesman warned that undersea cables in the Strait of Hormuz would be treated as legitimate targets in a future phase of conflict with the United States.

These "gray zone research activities" unfold alongside China's territorial disputes in the South China Sea with the Philippines and Vietnam. Beijing also claims Taiwan as a breakaway province, a position that keeps military tension elevated across the region.

Why This Matters

The findings shift the undersea cable threat from a hypothetical to a documented pattern. Telecom operators and governments that assumed cable routes were too remote to monitor now face evidence that foreign vessels are charting them systematically.

For the U.S. and its allies, the policy challenge is legal rather than military. Research ships in international waters enjoy freedom of navigation, so any response must rely on surveillance, attribution and diplomatic pressure rather than interdiction.

Cable consortia may need to rethink route secrecy and repair logistics. A mapped cable is a more vulnerable cable, and the CSIS data suggests several key Pacific links have already been surveyed in detail.

The Pacific Defense Forum, which reported on the analysis, framed the activity as part of China's push for undersea data dominance. That framing is likely to shape how navies and intelligence agencies allocate resources in the coming years.