The South China Sea’s next legal frontier: Ships without sailors

Unmanned warships blur legal boundaries as technology outpaces international law in contested maritime zones.

Pornomo Rovan Astri Yoga

10 September 20254 min read

The South China Sea has always been a flashpoint for regional tension, but the next phase of its militarisation might not be about aircraft carriers or submarines. It might be about ships with no sailors onboard at all.

China is already developing large unmanned surface vessels, including stealth-capable prototypes, while the United States – an ally of the Philippines and key partner for Taiwan – has considered giving “warship” status to some of its own unmanned vessels.

This trend suggests that if an armed conflict erupts in the South China Sea in the future, unmanned maritime systems (UMS) could play a decisive role.

The potential is obvious. UMS can conduct mine countermeasures, anti-submarine warfare, surface combat, electronic warfare, and many other tasks, all without risking the lives of sailors. As demonstrated in the Russia-Ukraine war, even relatively small unmanned sea drones can inflict serious damage. For China, which sees naval superiority as a crucial part of its regional strategy, unmanned warships might be a cost-effective way to expand its fleet. For the United States and its allies, they may represent both a deterrent and a force multiplier.

The absence of clear rules for converting unmanned maritime systems into warships is a legal gap with profound consequences.

But the legal questions are murky. Under international law, only warships and military aircraft possess “belligerent rights” in wartime. And to be classified as a warship, the Hague Convention VII of 1907 and Article 29 of the UN Convention on the Law of the Sea 1982 traditionally require a commanding officer and a crew physically onboard.

This raises the crucial dilemma: can an unmanned vessel ever be recognised as a lawful warship?

One interpretation says yes. If commanding officers and crews can exercise command and control remotely, then the spirit of the law – ensuring accountability and state responsibility – might still be fulfilled. In fact, in other contexts, the precedent for acknowledging the status of a warship without (living) crew onboard does exist. For example, sunken warships are still recognised as warships even though no living crew remains onboard. By analogy, perhaps unmanned vessels with remote command could qualify as warships too.

Yet, this alternative interpretation opens a Pandora’s box. If commanding officers do not need to be onboard, then converting a conventional ship into a warship becomes dangerously easy. Merchant ships, or even auxiliaries, could be reclassified as warships simply by linking them to remote naval officers and hoisting an ensign. When convenient, those links could be “disconnected” and the vessel could revert to civilian status – making it harder for opponents to know what is a lawful target. This uncertainty risks eroding long-standing protections for merchant shipping and neutral trade.

Sea-based unmanned warfare units on display at China's recent military parade in Beijing (Sheng Jiapeng/China News Service/VCG via Getty Images)

The acceptance of UMSs as having warship status also brings us to the tricky question of self-defence. At least two issues stand out. First, can a warship with no one on board really claim a right of self-defence? And second, if another state strikes an unmanned warship, can the flag state invoke self-defence – even though no human lives were lost in the attack?

In an asymmetric conflict, such as between China and a less technologically advanced claimant state, the interpretation of “warship” could itself become a weapon. The side with unmanned capabilities might insist its vessels are lawful warships. The other side, unable to deploy similar technology, could accuse its opponent of violating the laws of naval warfare. In retaliation, reprisals could be launched, escalating into a cycle where both sides bend or break international law to justify their actions.

This dynamic is not without precedent. In the early 20th century, the introduction of submarines sparked fierce legal debates. Britain, seeking to preserve its maritime dominance, opposed their use, while Germany and France pushed for legitimacy. Over time, state practice settled the matter, and because states could not resist the desire to benefit from such a useful and powerful armament, submarines became an accepted tool of war. We may be at the beginning of a similar trajectory with unmanned warships.

For other Southeast Asian claimant states – Vietnam, Malaysia, Indonesia, and Brunei – the prospect is troubling. Most have either no unmanned naval systems at all or only basic prototypes. If conflict erupts before they can catch up technologically, they may be pushed to contest the legality of unmanned warships simply as a survival strategy. The South China Sea could then become not only a battleground for ships, aircraft and drones, but also for competing legal narratives.

In the end, the law is struggling to keep pace with technology. The absence of clear rules for converting unmanned maritime systems into warships is a legal gap with profound consequences. Without international consensus, the South China Sea could become the testing ground for dangerous precedents in naval warfare.

Like the submarine debate a century ago, state practice will ultimately decide the matter. But given the stakes in the South China Sea, waiting for practice to evolve through conflict is a perilous gamble.

About the author

Pornomo Rovan Astri Yoga

Pornomo Rovan Astri Yoga is a legal scholar and naval officer specialising in the law of naval warfare, the law of the sea, and maritime security.

Topics

Brunei China Indonesia Malaysia Philippines Vietnam South China Sea Defence & security Cyber & technology