China mapping ocean floor for setting submarine warfare with US

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 US and its allies.

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 US stronghold of Guam, and around strategic stretches of the Indian Ocean, ship-tracking data reported by Reuters.

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 criss-crossed the waters between Sri Lanka and Indonesia, covering approaches to the Malacca Strait, a critical chokepoint for maritime commerce.

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 US 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.

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.

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.

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.

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.”