China is conducting a large-scale undersea mapping and monitoring campaign across the Pacific, Indian and Arctic oceans, collecting data that naval experts say could help it strengthen submarine warfare capabilities against the United States and its allies.

Data reviewed by Reuters shows the Chinese research vessel Dong Fang Hong 3, operated by Ocean University of China, spent 2024 and 2025 surveying waters near Taiwan, around the US military hub of Guam and in parts of the Indian Ocean.

The vessel also inspected Chinese ocean sensors near Japan and surveyed areas close to the Malacca Strait, a key global shipping route.

Chinese authorities say the missions involve mud surveys and climate research, but experts note that deep-sea mapping and the placement of ocean sensors can also provide valuable information for submarine navigation, concealment and detection of rival submarines.

The ship is part of a wider Chinese effort involving dozens of research vessels and hundreds of ocean sensors deployed across strategic maritime regions.

Analysts say such surveys help map seabed terrain and monitor water conditions like temperature, salinity and currents — factors critical for submarine operations and anti-submarine warfare.

Naval experts say the surveying activity is concentrated around militarily significant waters, including areas near the Philippines, Guam and Hawaii.

The information gathered could help China better deploy its submarines and track those of potential adversaries.

The effort also reflects China’s “civil-military fusion” strategy, where civilian scientific research supports military development.

Officials and analysts warn that the scale of the program could gradually erode the long-standing advantage held by the United States in understanding the underwater battlespace.