China’s UUV seizure was about undersea dominance


As the USNS Bowditch was recovering a UUV (unmanned underwater vehicle, or underwater drone) in the South China Sea on 15th December, a light-fingered Chinese Navy salvage ship reportedly called Naniju swooped in and took it in spite of repeated bridge-to-bridge demands to return the craft. Whilst this may have involved an early challenge to Trump, it is more likely to be connected with an emerging strategic battle over control of the undersea environment.

Immediately after the event, the US accused China of an ‘unlawful seizure’, and China later agreed to return the drone through ‘appropriate channels’ –– though not before President-elect Donald Trump had accused China of an ‘unpresidented [sic.] act,’ adding, ‘we don't want the drone they stole back.- let them keep it!’, in what is one of the most serious confrontations yet between the future US President and China.

Early interpretations of the event

When the story first broke on Friday, it wasn’t clear what kind of UUV had been pilfered, and I suggested that China might be hoping to reverse engineer an advanced US military drone it to bolster its own, more primitive UUV programme. After it was revealed that it was a commercially available glider costing only $150,000, this theory seems much less likely. However, what we don’t know – and I don’t imagine the Chinese crew would have known either – is whether the UUV they picked up had been fitted out with any additional components that might provide them with useful intelligence.

It was also not known on Friday precisely where the event took place, and many of us suggested that the act was a means of symbolically demonstrating China’s sovereignty over the seas that China claims within its proposed ‘Nine Dash Line’ - its claim to territorial waters. In such an instance, the legality of the act might have been down to a conflicting interpretation about whether or not it was operating in international waters, although the Permanent Court of Arbitration at the Hague has made it clear that the waters are not China’s.

South China Seas, showing nine dash line

Map of South China Seas showing approximate site of incident close to the Nine Dash Line, original source: UNCLOS and CIA, Quora, adjusted by Coll Ingram, 23 Dec 2016

Yet, it later emerged that the UUV was seized just off the coast of the Philippines, outside of boundaries of the Nine Dash Line. According to Distinguished Professor of Constitutional Law Julian Ku, this means that ‘unless there are new facts to be disclosed […] there is simply no plausible international legal basis for China’s action.’ While China might still be signalling about sovereignty, it’s not particularly clear or effective, and it suggests that some other motive might be at work.

Was it all about Trump?

The likelihood that China believed this particular ocean glider to be a national security threat is almost risible, meaning that this was more likely to be a symbolic act. However, its symbolism is contested and may have multiple layers.

Bonnie Glaser, director of the CSIS’ China Power Project, and others have suggested that this episode was intended to punish Donald Trump for his phone call with Taiwanese president Tsai Ing-wen in early December, and to test his resolve to act in the South China Sea, citing similar previous tests to new US administrations. This would be a test that Trump surely failed: in spite of his bluster, his (public) lack of interest in securing the drone’s return (‘let them keep it!’) – which is a process equally laden with symbolism – demonstrates a willingness to appease China and deals harm to the rules-based international order. China will surely need to test Trump again after the January 20th Inauguration Day, to ensure that appeasing words are matched by further inactions.

The Trump explanation goes some of the way, but I’d submit that this whole episode is not really about Trump. Rather, it’s the first surface-level symptom of an insidious undersea arms race to secure the strike capabilities of nuclear ballistic missile submarines and other conventional undersea forces.

The undersea arms race

Underwater drones are an emerging technology with wide potential applications, and both the US and Chinese military research establishments have shown clear interest. Gliders, such as the one China borrowed, can be programmed to autonomously collect oceanographic data, such as temperature, salinity, bathymetry (depth), etc. While this might seem harmless, when aggregated and processed using big data techniques, it can give a composite, high-resolution picture in space and time of what the oceans do, and intelligent interpolation models can be employed to fill in the gaps between each glider’s data points.

This information can then be mapped and used to predict where potential adversaries’ submarines will transit, since there are tactical advantages to hiding along temperature fronts and in other ocean anomalies. In future, it looks increasingly likely that bigger, faster, and more autonomous drones could be programmed to autonomously detect and pursue the submarines, including SSBNs equipped with nuclear ballistic missiles. For China, whose SSBNs are relatively undeveloped and very noisy, this is a real worry; the US could probably design and implement a UUV programme to trail its submarines within a decade or two.

This episode, therefore, should be read as China’s warning to the US and its allies against feeling too comfortable conducting UUV patrols in the South China Sea. As Dr Wu Riqiang argues, it is in China’s security interests to create a safe ‘bastion’ in the South China Sea, in which to protect its submarines – meaning keeping foreign UUVs away. This seizure may be a deliberate way of creating a precedent that allows China in future to interrupt smooth operation of foreign UUVs in the South China Seas. This perspective is clearly corroborated by the comments of one Chinese Navy commodore, whom the NYT has reported as saying, ‘the seized drone was part of an American effort to map and monitor conditions in the South China Sea to improve tracking of Chinese submarines.’

From a strategic stability perspective, it may be desirable to deter states from trailing nuclear-armed submarines. In peacetime, trailing Chinese strategic assets puts them at continuous risk and increase tensions; in a crisis, they could be rapidly targeted, increasing the likelihood that a Chinese submarine might use its nuclear weapons early if it fears that it might imminently be sunk.

What are the consequences of China’s UUV seizure?

By establishing a precedent of picking up ‘unknown’ US UUVs, China may feel emboldened to do the same again in future, citing vital security interests. As retired PLAN Admiral Yang Yi stated not long after, presumably coordinated by the Chinese state: ‘If China needs to take it, we’ll take it. [America] can’t block us.’ Thus, China may have strengthened the norm of disrupting UUV patrols in the interests of security, giving other states precedent to take similar actions against UUVs. It also clearly demonstrates the vulnerabilities of US UUVs in the recovery stage, and may lead to increased funding in the US for long-endurance technologies.

On the other hand, showing such brazen disregard for international law may haunt China. One outcome might be that the law around the status of unmanned underwater vehicles will crystallise. In his release on the incident, Pentagon Press Secretary Peter Cook clearly described the UUV as a ‘sovereign immune vessel’, the same status as a naval ship. This is not the first time the law of UNCLOS has been applied in this way – article 2.3.6 of the US Navy’s Commander’s Handbook on the Law of Naval Operations (2007) states the same – but it is perhaps the most high-profile test of its application.

This interpretation could have long-term benefits and costs for the US. If it catches on, it may mean that they can operate their UUVs remotely with less likelihood of them being hijacked or sunk, but it will also mean that China and other states will be able to claim the same status for their own UUVs. Were things to develop into a situation in which US submarines were being trailed by Russian or Chinese UUVs, there would be little the US could do about the situation short of breaking international law in the same fashion, which could be interpreted in a time of crisis as an act of war.

It also raises theoretical and normative questions around what the sovereign immunity of vessels means. Surely such a legal concept was created to protect important dignitaries and state assets, not semi-disposable military technologies that might just as well be governed by the immunity laws surrounding torpedoes? Does it really make sense for UUVs, some of which might be only a few feet long, to be governed by the same immunity laws as a large manned ship? This clearly needs an internationally recognised ruling or consensus document to avoid conflicts in this area.


While the glider has now been returned, long-harboured suspicions between the US and China over the undersea space in the South China Sea look set to grow more malignant and worrisome. This experience is a canary moment, indicating the need to develop regulations over the maritime technologies that could have significant impact on strategic stability. The invisibility of the undersea space in most people’s minds, and the apparent harmlessness of non-weaponised UUVs, hides critical questions that demand greater attention. With the US set to increase its UUV patrols in the South China Sea, it will be set it on a collision course with China unless dialogue about these matters is opened.

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  • Sebastian Brixey-Williams, Project Leader is a Project Leader at BASIC.
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