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Underwater Drone Incidents Point to China’s Expanding Intelligence Gathering

China’s apparent efforts to survey within other country’s territorial waters may go unchallenged.

The proliferation of small uncrewed underwater vehicles (UUVs) poses new challenges to governments. Even seemingly innocent civilian drones, used to gather hydrographic data, can pose a long-term security risk. The data is defence-civilian agnostic and can be used as readily for submarine warfare as for environmental research. There is no real way to be sure which, so even ‘research’ types that have been painted bright yellow are often viewed with suspicion. This has been highlighted by a UUV which recently turned up in Indonesia. It is just one among several, and they can be tied back to China.

China does not like other country’s UUVs in their waters. When Chinese fishing vessels find a foreign one, they can receive a life-changing reward from the government. In December 2016, a Chinese boat intentionally plucked a US Navy UUV out of international waters. It was only returned after a diplomatic exchange. It was a glider, a low-power type of UUV which travels with the current, collecting data. 

Four years after the US Navy glider incident, in December 2020, a broadly similar glider was found by Indonesian fishermen. There is one significant difference: this glider is Chinese. In fact, many of the gliders and other underwater vehicles washing up on beaches or found by fishing vessels are, too. 

China’s gliders are as ambiguous as any other state’s. Despite their high-visibility yellow paint and clear (and likely genuine) connection with civilian research, they are also associated with naval aims. In 2017, the South China Morning Post reported that China was speeding up the deployment of gliders in the South China Sea. Tellingly, the reason given was that this ‘could help reveal and track the location of foreign submarines’. 

The glider found in Indonesia was a Sea Wing (‘Haiyi’). This is the most commonly seen Chinese model and is roughly equivalent to Western types such as the popular Slocum G3 glider. Despite similarities, the Sea Wing has a unique appearance, so it can be confidently identified. It was discovered on 20 December near Selayar Island in the South Sulawes, which is on the eastern side of the Makassar Strait; one of several strategically important sea lines of communication (SLOC) which pass through Indonesia. It connects to the Lombok Strait, a narrow choke point connecting the Pacific and Indian Oceans. Together with the Sunda Strait and the Malacca Strait, which are also in Indonesia’s back yard, this may be a critical transit route for the Chinese People’s Liberation Army Navy (PLAN) in wartime. 

As well as data for submarine detection, or route planning, the gliders may be gathering other strategically relevant data. This could include, for example, information on natural resources which might be plundered in the future, or information on industry, gathered by sampling chemicals entering the sea from rivers. 

There were four earlier known instances of Sea Wings being found. On 16 November 2016, one was found near Quang Ngai in Vietnam. Then, on 12 February 2019, one was found near the northern tip of Bangka Island in Indonesia. This was quickly followed on 23 March 2019 by another in the Riau Islands. This one was helpfully labelled with the Chinese characters for ‘Sea Wing’ and ‘China Shenyang Institute of Automation, Chinese Academy of Science’. Given the short time interval, these two occurrences may have originated from the same mother ship. 

On 22 January 2020, one was found near the Masalembu Islands at the eastern end of the Java Sea, which is located on the eastern side of the Makassar Strait. This fourth example was likely still relatively newly deployed, complete with most of its yellow paint. This was followed in December by the Selayar Island example described above. 

These may have been placed in the water by China’s large fleet of survey ships. They range far and wide, even to the east coast of the US and to Antarctica. Analysis of their deployments with assistance from The Intel Lab, using data from, shows a number of transits through Indonesian waters in the past two years. These included several surveys of the Indian Ocean. The ships transited all three strategic waterways through Indonesia: the Malacca Strait, Sunda Strait and Lombok Strait. 

In December 2019, China deployed 12 Sea Wings in the Indian Ocean. The survey ship Xiangyanghong 06 was used, and is one of those analysed by The Intel Lab. But the mother ships do not have to be dedicated survey ships. These gliders are small and autonomous enough that they can be launched from almost any vessel, right down to a rubber dingy. Analysis of China’s survey ships is a strong indicator of where they are looking to deploy, but these gliders could also be launched covertly by other means. 

The Sea Wing is similar to other gliders. The basic principle that it uses is called ‘buoyancy propulsion’. Instead of using battery power to turn a screw to propel itself along, it uses forward momentum from first sinking and then rising. It has an oil bladder which is inflated to cause it to rise after it has sunk to the desired depth. The glider-like wings extend the distances travelled, and a small rudder gives it a limited capability to control its direction, although it is still largely at the mercy of the currents. When it reaches the surface, a long antenna is used to send data to base. All of this still requires a battery, as do its sensors, but its endurance is extremely long. 

All of the gliders found have carried a distinctive sensor on the outside of their fuselage. By analysing the available photographic evidence, these can be identified as measuring conductivity, temperature and depth (CTD). They are visually identical to a model made by a leading US glider manufacturer. These craft likely carry a range of other sensors too, many of which have both civilian and naval uses. 

But why are so many Sea Wing gliders turning up? There must be even more that are undiscovered, or found but not reported on. Generally, gliders are semi-reliable and users expect to lose some from time to time. They have a limited battery life, and some may sink or get washed up before they can be recovered. Normally, when a glider is found, the owning organisation is keen to get it back (or, at the very least, retrieve any data from the onboard memory). 

Perhaps the relatively high number of reported incidents is because the Sea Wing model is less reliable. But this doesn’t ring true for people familiar with the Chinese programme, as Chinese gliders are now typically on par with Western types. 

Another possibility is that China is deploying such a large number that more are bound to get lost. This is possible, but a third reason seems to fit the circumstances. China may be using them in a way where a higher loss rate is expected and tolerated. 

All four of the Sea Wings found in Indonesia were in territorial waters. This means that permission would have been required, whether for military or civilian purposes. Generally, a government representative would be aboard the survey ship to ensure that the activities are in line with the permissions given. The data would also, in many cases, be shared with the host country. Sometimes, extra stipulations are given, such as not allowing data sharing with third countries. Indonesia has in the past been reluctant to grant these permissions to foreign research vessels. 

When the most recent glider was found, the Indonesian military held a press conference where they displayed the vehicle. It was reported that they did not know its origin. This is despite it clearly being a Sea Wing, and essentially identical to three others previously found in Indonesian waters. So, this explanation seems unlikely. But it also suggests that it has not been claimed, meaning it likely does not relate to an authorised survey. 

It seems plausible, therefore, that China has deployed the gliders to gather strategic data in Indonesian territorial waters. The last two – which were found east of the Makassar Strait – bolster this theory, as does the fact that this has been done without the permission of the Indonesian government. That said, it can be difficult to link an individual glider to a specific operation. Their innocent-looking yellow paint and tendency to drift in the currents is the embodiment of plausible deniability. 

These easily deniable assets are now an emerging threat to states’ sovereignty, and one which is hard to stop. We may, therefore, expect to see an increasing number of Chinese UUVs turning up in unexpected places.

H I Sutton is an open source author, focusing on the maritime domain and particularly underwater warfare. He currently contributes to US Naval Institute News and, as well as his own Covert Shores website. 

The views expressed in this Commentary are the author's, and do not represent those of RUSI or any other institution. A minor amendment was made on 18 January 2021.


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