China is mapping the ocean floor as it prepares for submarine warfare with the U.S.

SYDNEY, March 24 (Reuters) – 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 United States 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 U.S. stronghold of Guam, and around strategic stretches of the Indian Ocean, ship-tracking data reviewed by Reuters shows. In October 2024, it…