SOURCE: AFI
China’s largest “silent” research vessel, the Dong Fang Hong 3, has concluded a month-long survey of the Ninety East Ridge in the Indian Ocean Region (IOR) and is now departing the area, according to posts on X by open-source intelligence analyst @detresfa_ on April 4, 2025. The Ninety East Ridge, a linear intraplate rise on the ocean floor, is considered an ideal location for submarine operations due to its unique underwater topography.
The vessel’s activities have reignited concerns about China’s expanding maritime ambitions in the IOR, particularly given the dual-use nature of its research operations, which could enhance the People’s Liberation Army Navy’s (PLAN) submarine capabilities while also serving scientific purposes.
The Dong Fang Hong 3, operated by China Ocean University in Qingdao, is a 5,000-tonne, 103-meter vessel delivered in 2019. It is designed for deep-sea and distant-water surveys, capable of operating at depths of up to 10,000 meters and deploying unmanned underwater vehicles (UUVs). What sets the Dong Fang Hong 3 apart is its designation as the world’s largest “silent” research vessel, a status earned through its military-grade low-noise propulsion systems, including electric azimuth thrusters and bow thrusters. These features minimize underwater noise, reducing disruption to marine life and enabling more accurate data collection. According to its chief designer, Wu Gang, a fish 20 meters beneath the vessel would not notice its presence, highlighting the ship’s stealth capabilities.
The vessel’s advanced technology, such as its ability to map ocean floors, study deep-sea ecosystems, and collect data on currents, salinity, and bathymetry, makes it a floating laboratory of unparalleled capability. However, these same capabilities have raised alarms among regional powers, particularly India, due to their potential military applications. The data gathered by the Dong Fang Hong 3 can enhance submarine operations, improve sonar performance, and even aid missile tracking—information that directly impacts maritime security in the IOR.
The Ninety East Ridge, a north-south underwater mountain range in the eastern Indian Ocean, has long been recognized as a critical area for submarine operations. Its relatively shallow waters and unique topography make it a challenging environment for submarines to navigate undetected, but also a strategically important one for mapping and understanding underwater conditions. The ridge’s proximity to key chokepoints like the Sunda and Lombok Straits, which serve as entry points for Chinese submarines into the IOR, further amplifies its significance.
The Dong Fang Hong 3’s month-long survey of the Ninety East Ridge, which concluded in early April 2025, follows a pattern of Chinese research vessels operating in strategically sensitive areas of the IOR. In January 2021, two Chinese vessels, the Xiang Yang Hong 01 and Xiang Yang Hong 03, conducted extensive surveys in the same region, with the latter reportedly “running dark” by shutting off its transponder in Indonesian waters. More recently, in March 2025, the Dong Fang Hong 03 was tracked alongside the Xiang Yang Hong 01 in the IOR, shortly after India’s successful K-4 submarine-launched ballistic missile (SLBM) test from INS Arihant in January 2025. This timing has fueled suspicions that China is using its research fleet to gather intelligence on Indian naval activities, particularly those involving its nuclear submarine fleet based near Visakhapatnam.
The data collected during such surveys—on ocean currents, salinity, temperature, and bathymetry—has clear dual-use applications. For civilian purposes, it contributes to scientific research on marine ecosystems and climate patterns. However, for military purposes, this information can optimize submarine stealth, improve sonar performance, and enhance navigation through complex underwater environments. The Ninety East Ridge’s strategic location makes it a prime target for such data collection, as it could aid Chinese submarines in evading detection by regional navies, including India’s, which considers the IOR its backyard.
The Indian Navy has been closely monitoring the Dong Fang Hong 3’s activities, as it has with other Chinese research vessels in the IOR. India’s concerns are well-founded, given China’s history of deploying survey ships during critical Indian defense activities. For instance, the Xiang Yang Hong 01 was tracked in the Bay of Bengal during India’s Agni-5 MIRV test in March 2024, and the Xiang Yang Hong 03 docked in the Maldives in 2024 amid strained India-Maldives ties under the pro-China government of President Mohamed Muizzu. These incidents suggest a deliberate pattern of Chinese vessels positioning themselves near India’s Exclusive Economic Zone (EEZ) or testing ranges to gather intelligence.
India’s naval presence in the IOR, bolstered by assets like P-8I maritime patrol aircraft and warships, has been instrumental in tracking these vessels. However, India’s own oceanographic research capabilities lag significantly behind China’s. While China operates a fleet of nearly 60 research vessels, India has only recently inducted its first modern survey vessel, INS Sandhayak, in February 2024, with a second, INS Nirdeshak, commissioned later that year. This disparity—roughly a 1:4 ratio in research vessel numbers—limits India’s ability to map its own waters and counter China’s subsurface activities effectively.
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