China’s Ministry of State Security posted a warning on WeChat on June 12 about foreign intelligence agencies fitting marine animals with underwater sensors to steal naval data. China’s MSS labeled the relevant section “spy turtles, spy fish.”
In December 2016, a Chinese naval vessel seized a US Navy ocean glider operating in the South China Sea — a torpedo-shaped autonomous drone about ten feet long collecting water temperature, salinity, and sound speed data. The same data China’s MSS now says foreign agencies are stealing through sensor-equipped marine animals.
China justified the seizure by claiming the vehicle was conducting surveillance. The Pentagon called it an unlawful seizure in international waters and demanded it back. China returned it five days later.
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Every major naval power is doing this, and all of them have reasons to be alarmed by what the others are doing, and the competition for underwater intelligence has grown into one of the least-covered and most consequential military contests of the past decade.
Gliders, buoys, wave gliders, seabed sensors, and sensor-equipped marine animals are all mapping the same thing. Water temperature, salinity, ocean currents, and seabed topography shape how sound moves underwater. That acoustic environment determines where submarines hide and how sonar finds them. A navy with a detailed, real-time picture of those conditions in contested waters holds a significant operational advantage.
The US Navy has operated the Marine Mammal Program since the early 1960s, training bottlenose dolphins and California sea lions for mine detection, harbor defense, and equipment recovery. Navy ocean gliders — the class of vehicle China seized in 2016 — number in the hundreds, run pre-programmed survey routes for weeks at a time, and transmit data via satellite. The Navy uses them to build the acoustic models underpinning anti-submarine warfare operations across the Pacific.
The Soviet Union ran a parallel marine mammal program. After the USSR collapsed, Ukraine inherited the dolphin fleet and sold the animals to Iran in 2000. Russia rebuilt its own program.
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In 2019, a beluga whale appeared on the Norwegian coast in a harness with a camera mount — an arrangement Norwegian researchers suspected came from Russian navy training. In 2023, British defense intelligence assessed that Russia was deploying trained dolphins in the Black Sea to counter Ukrainian combat divers.
Related: Satellite Photos Suggest Russia Has Deployed Navy-Trained Dolphins To Protect Black Sea Naval Base
The PLA calls its own project Transparent Ocean — the most ambitious underwater sensor architecture any nation has attempted. It has five integrated layers: a satellite constellation providing wide-area coverage that cues the lower layers; smart buoys and wave gliders stationed along strategically important straits; deep autonomous gliders patrolling the water column for weeks; seabed cable-connected observatories with docking and recharging infrastructure for unmanned vehicles; and an AI fusion center processing the combined picture.
China demonstrated the system at Joint Sea-2025 exercises near Vladivostok, where Chinese and Russian forces conducted joint anti-submarine warfare drills and shared hydro-meteorological and acoustic tracking data in real time — an early demonstration of what the PLA envisions as a persistent kill web across multiple oceans.
The seabed layer runs along the first island chain through the East and South China Seas. Analysts at the US Naval Institute describe it as an underwater Great Wall — a network of hydroacoustic sensors, seismometers, and navigation beacons that simultaneously serve scientific and military functions.
China operates 64 oceanographic research vessels, more than the combined US academic research and NOAA fleets, feeding data into the network continuously.
China’s civil-military fusion policy formally integrates civilian maritime industries into national defense functions, making its fishing and research fleet an extension of PLA Navy collection in ways that are difficult to monitor or counter.
The MSS is also offering 500,000 yuan to fishermen who report suspicious underwater devices. Millions of people working in the Chinese coastal waters are a surveillance network no military vessel can replicate.
In October 2024, the MSS warned that foreign agencies had planted navigation devices on the ocean floor to guide submarines through Chinese waters. China’s submarine fleet has grown fast — into seas the US and its allies have been mapping for decades. Transparent Ocean is Beijing’s attempt to even that score. The MSS campaign is an attempt to find what the other side has already left behind.
The 2016 glider seizure was just the moment the competition broke the surface. It has been running for decades, and the tools now range from seabed observatories to autonomous drone swarms to, per Beijing, “spy turtles, spy fish.”
