Philippines - December 31, 2025 The Philippine Coast Guard (PCG) detected the Chinese Research Vessel Tan Suo Er Hao operating approximately 19 nautical miles off the coast of Cagayan province in northern Luzon. The detection was made using Canada’s Dark Vessel Detection program. In response, PCG Commandant Admiral Ronnie Gil Gavan ordered a PCG Islander aircraft to conduct a Maritime Domain Awareness flight. The operation aimed to challenge the vessel’s presence, verify whether it was conducting marine scientific research without prior consent from the Philippine government, and assert Philippine sovereign rights within its Exclusive Economic Zone. The CRV Tan Suo Er Hao is an 87.25-meter advanced deep-sea research vessel operated by the Institute of Deep-sea Science and Engineering under the Chinese Academy of Sciences. It serves as a mothership for manned and unmanned deep-sea submersibles and supports comprehensive deep-sea operations. Monitoring indicated the vessel departed from Hainan province, China, earlier this month and transited through the western Philippine EEZ. During the MDA flight, the PCG aircraft sighted the CRV heading eastward at coordinates Latitude 18°34.021′ N, Longitude 123°17.042′ E, about 55.78 nautical miles east of Santa Ana, Cagayan. The PCG pilot issued multiple radio challenges to the vessel, asking about its intentions and reminding it of the requirement for prior consent for marine scientific research in Philippine waters. The CRV Tan Suo Er Hao did not respond. The Philippine Coast Guard continues to monitor and challenge unauthorized activities within the Philippine EEZ in line with directives from President Ferdinand Marcos, Jr., to uphold national sovereignty and maritime laws.