Chinese research vessels have been systematically mapping large areas of the Pacific, Indian, and Arctic oceans in recent years, activities that naval experts say could tremendously boost Beijing’s submarine operations.
While the world remains invested in the ongoing war between the US and Iran, Reuters published a detailed report explaining China’s sustained effort to map and monitor the seafloors of the Pacific, Indian, and Arctic Oceans, and to gather extensive knowledge of marine conditions.
The data is reportedly being gathered with an eye on submarine warfare in distant waters.
The report cites the example of a research vessel, Dong Fang Hong 3, operated by Ocean University of China, which was purportedly conducting climate research and mud surveys. However, it also cites a scientific report co-authored by academics from Ocean University that purportedly states the vessel conducted substantial deep-sea mapping, clearly indicating the mission’s military intent.
Waters That The Dong Fang Hong 3 Studied
Analysing data from a ship-tracking platform built by Starboard Maritime Intelligence, the Reuters report discovered that Dong Fang Hong 3 spent 2024 and 2025 sailing back and forth across the seas near Taiwan, the frontline US territory of Guam, and the strategic stretches of the Indian Ocean Region (IOR).
Notably, China views Taiwan as a renegade Chinese province and has vowed to occupy it, with force if necessary. And, military analysts believe that a Chinese invasion of Taiwan will inevitably draw the US into a conflict upon the latter’s intervention, and further escalate into a region-wide war as US allies in the Indo-Pacific aid Washington or join its war effort.
This essentially means that the Chinese research vessel was mapping waters that could be subject to military deployments during a conflict.
The report also revealed that the Dong Fang Hong 3, equipped with advanced Chinese ocean sensors, detected underwater objects near Japan in October 2024 and returned to the same area in May 2025. Separately, it crisscrossed the waters between Indonesia and Sri Lanka in March 2025, passing near the Strait of Malacca.
Japan is the closest US ally in the Indo-Pacific and home to the US Seventh Fleet. Additionally, China and Japan remain embroiled in territorial disputes in the East China Sea, and Tokyo has repeatedly flagged the increased Chinese military presence near its territorial waters.
That said, the presence of the Chinese vessel near the Strait of Malacca is also noteworthy, given that it is a highly strategic chokepoint in the Indian Ocean Region (IOR) and is of increased significance to China, as about 80% of its energy imports pass through this waterway.
This is not the first time that a report or agency has flagged these activities. In 2023, for instance, Chinese research and oceanographic vessels were surveying the Indian Ocean Region (IOR), as eralier reported by the EurAsian Times.
In 2025, citing the Starboard Maritime Intelligence data, a New York Times report stated that the Chinese research vessels frequently investigated the ocean floor east of Taiwan’s maritime boundary and roughly 400 kilometres east and west of Guam. These were “waters that China’s navy considers strategically vital,” the report emphasised.
However, according to ship-tracking data, China is currently concentrating its seabed mapping efforts on strategically significant waters around Guam and Hawaii, the Philippines, and US military installations on Wake Island in the North Pacific.
Both Guam and Hawaii are US territories that are anticipated to be used as launchpads for undertaking attacks on China in the event of a conflict. Meanwhile, the Philippines is a key US ally in the South China Sea, with a host of military bases accessible to Washington.
Is China Preparing For Submarine Warfare?
Navy officials and experts believe that the Dong Fang Hong 3’s detailed ocean mapping and sensor placements are helping China build a comprehensive understanding of the subsea environment. This data would enable the Chinese navy to deploy its submarines more effectively in a potential conflict while improving its ability to detect and track enemy submarines.
In fact, the Dong Fang Hong 3 is not working in isolation. Instead, it is part of a larger ocean mapping and monitoring project that uses hundreds of sensors and dozens of research vessels.
A typical Chinese survey vessel can collect data for seabed mapping, record hydrological data to understand the underwater environment, gather intelligence on subsea cables, and record telemetry data from missile firings, among other tasks. This information could be vital for submarine warfare.
“To gather information about underwater terrain, research vessels map the sea floor while travelling 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,” the report noted. Additionally, an extensive review conducted by the publication reportedly revealed that at least 8 of the vessels that it had tracked had conducted seabed mapping, and another 10 had carried mapping equipment.
Seabed mapping refers to the process of measuring and mapping the topography of the ocean floor. This could apparently help assess the ocean floor, whether it is soft or rocky, as submarines sometimes descend to the bottom of the ocean, turn off their communications, and sit quietly in a conflict situation or a potential contingency.
Explaining why China needs to gather undersea data, a former Indian Navy submariner, Commodore Anil Jai Singh (retd), said: “China has been expanding its submarine operations far and wide in previously unexplored oceans. Therefore, it needs to monitor the underwater environment. The sound velocity in water, which is crucial for submarine navigation and sonar, changes with salinity, pressure, and temperature. Since these three factors are not constant, Chinese vessels keep revisiting the same areas to gather as much data as possible and better understand and analyse trends. This is not just for their own submarine deployment, but also for detection and anti-submarine warfare.”
“It is meant to ensure that the enemy does not have an advantage in oceans that China does not quite operate in—yet,” he added. Additionally, the scientific research vessels can also use their instruments for naval surveillance, gathering information on nearby foreign military installations and vessels.
According to naval experts, Commanders require data on undersea topography to prevent collisions. This, perhaps, makes sense as we recall the fate of USS San Francisco, which collided with a seamount at very high speed in 2005.
The Reuters report further states that China has conducted its most thorough ocean surveys to the east of the Philippines, along the First Island Chain, a chain of territories that stretches from the Japanese islands in the north through Taiwan and Borneo in the south. The chain forms a natural barrier between China’s coastal seas and the Pacific.
Peter Leavy, a former Australian naval attaché to the United States and current head of the Australian Naval Institute, stated, “They’re paranoid about being boxed in to the First Island Chain.” China’s charting reveals a “desire to understand the maritime domain so they can break out”, he added.
In addition to mapping this area and the US military outposts like Guam and Hawaii, the seafloor north and west of Alaska, a crucial sea route into the Arctic, has also been explored by Chinese ships. Beijing has stated that it wants to become a polar great power by the 2030s and has designated the Arctic as a strategic frontier.
Former US Navy submariner and adjunct senior fellow at the Centre for a New American Security, Tom Shugart, believes that Beijing’s increasing underwater capabilities and comprehensive surveys are “symptomatic of China’s rise as a premier maritime power.”
In addition to studying hydrography and mapping the seafloor, China has also gained access to real-time data on subsea movements and water conditions, thanks to an expanded network of sensors, as highlighted by Ocean University and the Institute of Oceanology, a division of the Chinese Academy of Sciences.
“Many sensors are placed in sensitive locations. For example, Reuters recently reported on a U.S. effort to fortify a key strait between Taiwan and the Philippines to cut off Chinese access to the Pacific. Ocean University studies show that China has deployed advanced sensors in parts of the strait through which U.S. submarines would move to reach the South China Sea,” the report states.
When probed on the issue of placing sensors by this correspondent, Commodore Singh said, “China is laying seabed sensors that are connected to satellites for collecting data on the movement of enemy undersea assets. This data is collated and sent to the command, where it is analysed for anti-submarine warfare.”
Meanwhile, Brookes, the director of the US Office of Naval Intelligence, said China is building undersea surveillance networks that “gather hydrographic data – water temperature, salinity, currents – to optimise sonar performance and enable persistent surveillance of submarines transiting critical waterways like the South China Sea.”
Together, China’s mapping gives it sophisticated tools to detect rival submarines and deploy its own in some of the world’s most contested waters.
“This is a manifestation of China’s far-seas reach,” said Collin Koh, a senior fellow in maritime security at Singapore’s RSIS Institute of Defence and Strategic Studies. “They now have a reasonably good picture of the maritime domain they hope to operate in, either in peacetime or in war.”
The development comes on the back of a rapidly expanding submarine fleet and undersea capability within the Chinese People’s Liberation Army Navy (PLAN). China’s submarine strength will rise in the coming years. A 2023 US Department of Defence (DoD) report anticipates that China will grow its submarine force to 80 units by 2035, with nearly 20 of those subs nuclear-powered.
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