By Pete Mckenzie SYDNEY, March 24 (Reuters) - China is conducting a vast undersea mapping and monitoring operation across the Pacific, Indian and Arctic oceans, building detailed knowledge of marine
China Expands Ocean Floor Mapping for Possible Submarine Warfare with U.S.
By Pete Mckenzie
China’s Undersea Mapping Operations and Strategic Implications
SYDNEY, March 24 (Reuters) - China is conducting a vast undersea mapping and monitoring operation across the Pacific, Indian and Arctic oceans, building detailed knowledge of marine conditions that naval experts say would be crucial for waging submarine warfare against the United States and its allies.
Key Research Vessel Activities
In one example, the Dong Fang Hong 3, a research vessel operated by Ocean University of China, spent 2024 and 2025 sailing back and forth in the seas near Taiwan and the U.S. stronghold of Guam, and around strategic stretches of the Indian Ocean, ship-tracking data reviewed by Reuters shows. In October 2024, it checked on a set of powerful Chinese ocean sensors capable of identifying undersea objects near Japan, according to Ocean University, and visited the same area again last May. And in March 2025, it criss-crossed the waters between Sri Lanka and Indonesia, covering approaches to the Malacca Strait, a critical chokepoint for maritime commerce.
Scientific and Military Objectives
According to the university, the ship was carrying out mud surveys and climate research. But a scientific paper co-written by Ocean University academics shows it has also conducted extensive deep-sea mapping. Naval-warfare experts and U.S. Navy officials say the type of deep-sea data being collected by the Dong Fang Hong 3 – via mapping and placement of sensors in the ocean – is giving China a picture of the subsea conditions it would need to deploy its submarines more effectively and hunt down those of its adversaries.
Broader Mapping Efforts
The Dong Fang Hong 3 isn't operating alone. It is part of a broader ocean mapping and monitoring operation involving dozens of research vessels and hundreds of sensors. In tracing this effort, Reuters examined Chinese government and university records, including journal articles and scientific studies, and analyzed more than five years of movement by 42 research vessels active in the Pacific, Indian or Arctic oceans using a ship-tracking platform built by New Zealand company Starboard Maritime Intelligence.
Civilian and Military Dual-Use
While the research has civilian purposes – some of the surveying covers fishing grounds or areas where China has mineral prospecting contracts – it also serves a military one, according to nine naval-warfare experts who reviewed Reuters' findings.
Seabed Mapping Techniques
To gather information about underwater terrain, research vessels map the sea floor while traveling back and forth in tight lines. The tracking data shows that type of movement by the vessels Reuters tracked across large sections of the Pacific, Indian and Arctic oceans.
At least eight of the vessels Reuters tracked have conducted seabed mapping, while another 10 have carried equipment used for mapping, according to a review of Chinese state media articles, vessel descriptions published by Chinese universities, and press releases by government organizations.
Military Significance
The vessels' survey data "would be potentially invaluable in preparation of the battlespace" for Chinese submarines, said Peter Scott, a former chief of Australia's submarine force. "Any military submariner worth his salt will put a great deal of effort into understanding the environment he's operating in."
The ship-tracking data show that China's seabed-surveying effort is focused in part on militarily important waters around the Philippines, near Guam and Hawaii, and near U.S. military facilities on Wake atoll in the north Pacific.
Strategic Intentions and Civil-Military Fusion
"The scale of what they're doing is about more than just resources," said Jennifer Parker, an adjunct professor of defense and security at the University of Western Australia and former Australian anti-submarine warfare officer. "If you look at the sheer extent of it, it's very clear that they intend to have an expeditionary blue-water naval capability that also is built around submarine operations."
Moreover, Parker and other experts added, even where data is gathered for scientific purposes, the integration of civilian scientific research and military technology development has become a key focus of the Chinese government under President Xi Jinping. Beijing refers to this approach as "civil-military fusion."
International Responses and Concerns
China's ministries of defense, foreign affairs and natural resources didn't respond to requests for comment about the seabed mapping and ocean-monitoring activities.
The U.S. Defense Department didn't respond to questions from Reuters.
U.S. Intelligence and Strategic Concerns
In testimony to a congressional commission this month, Rear Admiral Mike Brookes, the commander of the U.S. Office of Naval Intelligence, said China had dramatically expanded its surveying efforts, providing data that "enables submarine navigation, concealment, and positioning of seabed sensors or weapons." He added that "potential military intelligence collection" by Chinese research vessels "represents a strategic concern."
America recently overhauled its own efforts to map and monitor the ocean, but it typically does so with military vessels that are allowed to turn off the tracking system monitored by civilian software. China's civilian survey ships also sometimes disable tracking, meaning its campaign may go further than Reuters could determine.
Scale and Impact of China’s Mapping Campaign
This is the first time the extent of China's mapping and monitoring across the Pacific, Indian and Arctic oceans has been reported. Previous reporting has revealed a portion of the effort around Guam and Taiwan, and in parts of the Indian Ocean.
Expert Opinions
"It is frankly astonishing to see the enormous scale of Chinese marine scientific research," said Ryan Martinson, an associate professor specializing in Chinese maritime strategy at the U.S. Naval War College.
"For decades, the U.S. Navy could assume an asymmetric advantage in its knowledge of the ocean battlespace," added Martinson. China's efforts "threaten to erode that advantage. It is obviously deeply concerning."
'PARANOID ABOUT BEING BOXED IN'
The data that Ch
