China expands seabed mapping operations with military implications
China has carried out an extensive underwater mapping campaign across the Pacific, Indian, and Arctic oceans, building detailed knowledge of seabed conditions that analysts say could support future submarine warfare against the United States and its allies, according to a Reuters investigation.
The report tracked the movements of 42 Chinese research vessels over more than five years using maritime data. It found that dozens of ships systematically mapped the seabed in strategically important regions. At least eight vessels conducted direct seabed mapping, while ten others carried equipment designed for such surveys, based on a review of Chinese state media and academic publications.
One vessel, the Dong Fang Hong 3, operated by the Ocean University of China, played a central role. It spent 2024 and 2025 sailing repeatedly near Taiwan, around the US military hub of Guam, and through key areas of the Indian Ocean. In March 2025, it surveyed waters between Sri Lanka and Indonesia, including approaches to the Strait of Malacca, a major global shipping route. While the university described the missions as sediment and climate research, scientific publications linked to the vessel confirm that detailed seabed mapping was also conducted.
Experts say such data has clear military value. Former Australian submarine commander Peter Scott said the information gathered could be critical for preparing underwater battlefields, helping submarines navigate, remain concealed, and deploy sensors or weapons more effectively.
US officials have raised concerns about the strategic implications. Speaking before Congress earlier this month, Rear Admiral Mike Brookes of the US Office of Naval Intelligence said China has significantly expanded its ocean survey efforts. He noted that the collected data enables underwater navigation, improves concealment, and supports the placement of seabed systems. He also warned that the potential military intelligence gathered by research vessels represents a growing strategic concern.
Brookes added that China is developing underwater monitoring networks that collect hydrographic data such as temperature, salinity, and ocean currents. These factors are critical for optimizing sonar performance and tracking submarines moving through key waterways, including the South China Sea.
Ship tracking data shows that Chinese survey activity is concentrated in areas of high military relevance. These include waters near the Philippines, around Guam and Hawaii, and close to US military installations on Wake Atoll in the North Pacific.
The mapping campaign forms part of a broader effort by China to challenge long-standing US dominance in underwater operations. Analysts say Beijing is building what has been described as an underwater sensor network, combining fixed and mobile systems across strategic maritime chokepoints.
At the same time, China is upgrading its submarine fleet with next generation attack submarines and ballistic missile submarines. Experts say the scale and scope of these efforts point to ambitions beyond coastal defense, indicating a push toward sustained deep sea naval capabilities.
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