China has dramatically expanded its deep-sea mapping efforts in the Western Pacific, conducting detailed seabed surveys off Taiwan’s east coast and around Guam—both key flashpoints in any future conflict with the United States. While presented as scientific research, the operations are drawing sharp concern from regional governments and defense experts who say the data could enhance China's undersea warfare capabilities.

Civilian Vessels, Strategic Missions

At least six Chinese research ships—including the Xiang Yang Hong 6 and Da Yang Hao—made dozens of tightly-patterned passes through waters near Taiwan and Guam in 2024, some just outside Taiwan’s 12-nautical-mile territorial limit. According to maritime tracking data, these vessels moved slowly in grid formations, a technique typical of sonar-based bathymetric surveys used to map the ocean floor.

Though the ships are civilian and operated by universities or government institutes, experts warn they serve dual-use purposes. “It appears that China is trying to collect bathymetric data... without appearing like it is conducting a bathymetric survey,” said Ryan D. Martinson of the U.S. Naval War College.

Targeting the Pacific’s Strategic Chokepoints

Taiwan’s eastern coast hosts critical air and naval bases. Should conflict erupt, control of surrounding waters could be decisive. The seafloor there is shaped by the Kuroshio Current and steep underwater shelves—conditions that complicate submarine stealth and detection. Understanding this terrain gives China an edge in planning sub-surface maneuvers, experts say.

Farther east, near the U.S. territory of Guam—a hub for American bombers, submarines, and radar systems—Chinese vessels mapped an area larger than the UK. While China has registered parts of the seabed near Guam for mineral exploration, much of the activity occurred outside those zones, prompting speculation that the real purpose is military.

“These surveys may have been conducted for other purposes,” said Christopher Kelley, a retired University of Hawaii oceanographer. Former U.S. Navy officers argue the data could aid Chinese submarines in hiding, navigating, or even launching attacks in the event of war.

Rising Regional Pushback

Countries across the Asia-Pacific are increasingly alarmed. Taiwan has accused China of deploying surveillance buoys, while the Philippines tracked and denounced illegal Chinese surveys in its exclusive economic zone. Australia and Vietnam have also objected to similar incursions.

“China’s expanding maritime reach deserves close scrutiny,” said Jennifer Parker, a former Australian naval officer now at the National Security College. “Its ‘research’ vessels map seabeds, deploy sensors, and pave the way for submarine operations.”

Despite official complaints, China’s survey efforts show no sign of slowing. Last month, new Chinese ships resumed grid-pattern operations east of Guam.