China's Undersea Mapping Campaign Challenges the US Submarine Advantage

42 Research Ships and a Growing Underwater Network

China has deployed 42 research vessels across the Pacific, Indian and Arctic oceans in a sweeping effort to map the seabed and measure the water conditions that help submarines hide or expose them to detection. Tracking records covering more than five years show activity near Taiwan, Guam, Hawaii, the Philippines and other locations important to United States naval operations.

At least eight of those vessels have carried out confirmed seabed mapping, while another ten carry equipment capable of doing that work. Alongside the ship surveys, Chinese institutions have developed networks of underwater sensors, including hundreds deployed east of Japan, east of the Philippines and around Guam.

As of March 26, 2026, the campaign presents a growing challenge to an advantage the US Navy has held for decades: detailed knowledge of the underwater environment in which its submarines operate. Maps of underwater mountains, combined with measurements of temperature, salinity and currents, can help commanders find hiding places, improve sonar performance and anticipate where another country's submarines might travel.

Ryan Martinson, an associate professor specializing in Chinese maritime strategy at the US Naval War College, described the scale of Beijing's marine scientific research as frankly astonishing. Western defense analysts see the effort as one of the most comprehensive seabed surveying campaigns in recent naval history.

The activity reaches beyond China's nearby seas. Research ships have examined approaches to the Malacca Strait, waters near Australian submarine routes, and areas west and north of Alaska. The locations connect three priorities: access to the open ocean, protection of maritime trade and knowledge of waters used by potential naval opponents.

China's research institutions also describe ties between their scientific work and national defense. Those connections help explain why a civilian vessel measuring ocean conditions can attract close attention from foreign navies.

Where the Research Fleet Has Been Working

The Dong Fang Hong 3, operated by Ocean University of China, is a central example. During 2024 and 2025, it repeatedly surveyed waters near Taiwan, Guam and important stretches of the Indian Ocean. Ship tracking showed it moving back and forth in closely spaced lines, a pattern associated with systematic seabed mapping.

In October 2024, the vessel inspected powerful ocean sensors near Japan that were capable of identifying underwater objects. It returned to the same location in May 2025. In March 2025, it crisscrossed waters between Sri Lanka and Indonesia, covering approaches to the Malacca Strait, a critical passage for maritime commerce.

Analysis of movement records from Starboard Maritime Intelligence identified the wider fleet of 42 vessels. The ships belong to Chinese state bodies, including the Ministry of Natural Resources, or research institutions affiliated with the state.

Some vessels sometimes turn off their tracking systems, leaving gaps in the visible record. The full extent of their activity may therefore be larger than the documented movements. The recorded operations already include sensitive waters around the Philippines, Hawaii and US facilities on Wake atoll in the northern Pacific.

How Ocean Conditions Shape Submarine Warfare

Submarines navigate and conceal themselves within a few hundred meters of the surface, where the shape of the seabed and the properties of the water affect detection. A map of the ocean floor helps a commander avoid underwater mountains, known as seamounts, and understand where terrain may provide cover.

Sonar uses sound to detect objects underwater. Sound waves bend and bounce differently as they encounter changing water density and seabed contours. Temperature layers, variations in salinity, and currents influence the underwater environment, creating areas where a submarine may be easier or harder to find.

Tom Shugart, a former US submarine commander now at the Center for a New American Security, explained that the underwater landscape changes the movement of sound. The same submarine operation may remain concealed in one location and become exposed in another because the water carries sound differently.

Peter Scott, former chief of Australia's submarine force, described the value of survey information for preparing an area for military operations:

The vessels' survey data would be potentially invaluable in preparation of the battlespace. Any military submariner worth his salt will put a great deal of effort into understanding the environment he's operating in.

Scott's assessment applies to both sides of underwater warfare. Environmental data helps submarines select routes and hiding places, while forces hunting them can use it to improve detection. China's surveys could therefore support its own submarine deployments and operations aimed at finding American or allied vessels.

The Transparent Ocean Project

Wu Lixin, a scientist at Ocean University of China, proposed the transparent ocean project around 2014. The idea was to build extensive networks of sensors, buoys and arrays beneath the sea that could monitor water conditions and underwater movement in real time.

Shandong provincial officials said the proposal quickly received at least $85 million in support from the provincial government. The project began in the South China Sea, where Ocean University now says it has constructed an observation system covering the deep sea basin.

Chinese government agency records describe its expansion into the Pacific and Indian oceans. Hundreds of sensors have been deployed east of Japan, east of the Philippines and around Guam. Indian Ocean documents describe an array ringing India and Sri Lanka, including installations along the Ninety East Ridge, one of the world's longest underwater mountain ranges.

Rear Admiral Mike Brookes, commander of the US Office of Naval Intelligence, told a congressional commission that China is building underwater surveillance networks to gather hydrographic data, meaning information about the physical features and conditions of the sea. He said the data could improve sonar performance and support persistent surveillance of submarines passing through critical waterways such as the South China Sea.

Some naval experts caution that transmitting information underwater in real time presents technical difficulties. Even when information arrives later, measurements can still help build knowledge of ocean conditions and adversary submarine operations. The project combines repeated observations from fixed instruments with the wider reach of ships conducting surveys.

Why the First Island Chain and Guam Matter

Waters east of the Philippines have received China's most comprehensive ocean surveying. They lie along the First Island Chain, a line of territories running from the Japanese islands through Taiwan and south to Borneo. Largely controlled by American allies, the chain forms a natural barrier between China's coastal seas and the open Pacific.

Peter Leavy, formerly Australia's naval attache to the United States and now president of the Australian Naval Institute, observed that China appears paranoid about being boxed in by this chain. He interpreted the extensive mapping as a desire to understand the maritime environment well enough to reach the open ocean.

Guam is another focus. American submarines powered by nuclear reactors are stationed there, and Chinese vessels have mapped surrounding waters. Surveys around Hawaii extend the activity to another major US regional hub.

Chinese ships have also examined an underwater ridge north of a naval base in Papua New Guinea to which the United States recently gained access. Around Christmas Island, an Australian territory, they have surveyed waters on routes between the South China Sea and an important Australian submarine base.

Those locations connect the mapping effort to naval movements across the wider Indo-Pacific. Knowledge gained near a base can help explain its underwater approaches, while surveys along connecting routes can support operations farther from China's coastline.

Trade Routes Draw Attention to the Indian Ocean

The Indian Ocean carries Chinese imports of oil and other resources from the Middle East and Africa. Chinese vessels have mapped large areas of it, extending the campaign into waters central to both commercial shipping and regional naval activity.

Jennifer Parker, an adjunct professor of defense and security at the University of Western Australia and a former Australian officer specializing in warfare against submarines, identified China's dependence on maritime trade as a key vulnerability. She said the extensive surveying indicates Beijing will likely conduct more submarine operations in the Indian Ocean to protect those supply lines while monitoring regional powers, including India.

The sensor array along the Ninety East Ridge lies across approaches to the Malacca Strait, through which much of China's oil supply passes. Its position gives the network potential value for monitoring vulnerabilities along Chinese supply routes and movements by adversary submarines through the chokepoint.

India has particular concerns about Chinese research near the Bay of Bengal, where its fleet of submarines powered by nuclear reactors is based. India has also long sought to establish itself as a regional provider of hydrographic services, giving the collection of maritime data an additional dimension of regional competition.

Chinese ships have surveyed the seabed west and north of Alaska as well. Those waters form an important route into the Arctic, where Beijing has declared its ambition to become a polar great power by the 2030s. The Arctic operations widen a campaign already stretching across the Pacific and Indian oceans.

Scientific Institutions Describe Their Defense Role

President Xi Jinping's government has made the integration of civilian scientific research and military technology development a central priority. Beijing calls the approach civil-military fusion. In this campaign, institutions operating research vessels and ocean observation networks also maintain explicit connections with naval organizations.

Ocean University's president publicly celebrated the institution's close ties to China's navy in 2021 and its commitment to building a maritime power and supporting national defense.

Zhou Chun, an Ocean University researcher who oversees the Indian and Pacific ocean sensor arrays, described the connection in a 2025 press release. He said his work had shown him the rapid development of his country's maritime defense and military capabilities. He also pledged to turn the most advanced scientific and technological achievements into new types of combat capabilities for the military at sea.

Wu now oversees the observation network through the Qingdao National Laboratory for Marine Science and Technology. Its partners include China's Naval Submarine Academy. These institutional links place the surveying effort within a broader relationship between civilian ocean science and military planning.

Sri Lanka Moves to Control Maritime Research

Sri Lanka introduced a moratorium lasting 12 months on visits by foreign research vessels after Chinese ship visits drew loud protests from New Delhi. The most recent visit cited in that dispute was the Shi Yan 6's arrival in October 2023.

The Sri Lankan government also moved to cancel an agreement between a Chinese institute and a local university. That arrangement had given China easy access to Sri Lankan waters and hydrographic information.

A new agency under Sri Lanka's Ministry of Defence was created to supervise hydrographic research. The measures sought to give Sri Lanka greater sovereign control over information about its own maritime territory, amid wider regional concerns about the security value of ocean surveys.

The developments described across the campaign span several years:

• Around 2014: Wu Lixin proposed the transparent ocean project, which quickly received at least $85 million in support from Shandong province.
• 2021: Ocean University's president celebrated the university's close ties to China's navy and its role in maritime power and national defense.
• October 2023: The Shi Yan 6 visited Sri Lanka, drawing protests from New Delhi.
• 2024 and 2025: The Dong Fang Hong 3 repeatedly surveyed near Taiwan, Guam and parts of the Indian Ocean.
• October 2024: The Dong Fang Hong 3 inspected underwater sensors near Japan.
• March 2025: The vessel surveyed waters between Sri Lanka and Indonesia along approaches to the Malacca Strait.
• May 2025: The ship returned to the sensor location near Japan.
• 2025: Zhou Chun described links between his ocean research and China's developing maritime military capabilities.

Rocket Tests Point to Another Use for the Seabed

Chinese scientists have tested the ignition of a solid rocket engine at a depth of 200 meters underwater. Engineers from the Mechano-Electrics Engineering Institute and the Key Laboratory of Underwater Intelligent Equipment published their findings in the Chinese journal Tactical Missile Technology, which uses peer review.

The work described an experimental platform that simulates conditions in deep water. Standard missiles launched from submarines typically fire from around 30 meters, making the tested depth more than six times that figure.

If developed into operational systems, the technology could support missile launch facilities fixed to the ocean floor. Such installations would give Beijing additional military options beneath the sea. An operational deployment date was not given.

Detailed seabed information would be useful for planning where underwater equipment could operate. The rocket experiment adds a potential weapons application to a campaign already collecting the environmental knowledge needed for submarine navigation, concealment and detection.

Underwater Cables and Australia's Concerns

Taiwan depends almost entirely on undersea cables for internet connectivity. That reliance makes the island vulnerable to targeted cable cutting, which could create a digital quarantine by sharply reducing its communications with the outside world.

Jason Hsu, a researcher cited in defense analyses, suggested that the People's Liberation Army could sever key cable clusters and reduce Taiwan's bandwidth by up to 99%. Such a disruption could isolate the island and interfere with coordination among its allies.

Detailed knowledge of the seabed can support capabilities for disrupting underwater infrastructure. Mapping that helps locate suitable sensor positions or submarine routes can also provide useful information about areas containing cables.

The Tansuo Yi Hao, another Chinese research vessel, circumnavigated Australia and paused over the Diamantina Trench. The location could potentially be used to service acoustic sensors on the seabed or gather intelligence about underwater cables.

Australian Prime Minister Anthony Albanese said publicly that he would prefer such vessels were not present in Australian waters. His response reflects the regional concern prompted by research activity whose information can serve scientific work and military operations.

The Bottom Line

• Tracking records covering more than five years identified 42 Chinese research vessels active across the Pacific, Indian and Arctic oceans.
• At least eight vessels conducted confirmed seabed mapping, and another ten carried equipment capable of that work.
• The transparent ocean project received at least $85 million in support from Shandong province and expanded into observation networks across several strategic regions.
• Surveys and sensors cover waters near the First Island Chain, Guam, Hawaii, Malacca Strait approaches and routes important to Australian submarines.
• Temperature, salinity, currents and seabed terrain affect sonar, giving environmental information value for both hiding submarines and finding them.
• Chinese research institutions have described direct connections between ocean science, national defense and developing military capabilities.
• Sri Lanka restricted foreign research vessel visits and strengthened supervision of hydrographic research after concerns over Chinese activity.
• A rocket ignition test at 200 meters and concerns over Taiwan's cables point to potential military uses of the seabed beyond submarine operations.