BEIJING has released a fleet of 12 underwater spy drones to scour the South China Sea — and report back instantly on anything significant they may find.

The torpedo-shaped drones are called ‘Haiyi’, or ‘sea wings’.

The Chinese research vessel Kexue deployed a swarm of 12 of them at the weekend, ostensibly to collect environmental data. They’re expected to remain active for about a month.

“The gliders have collected detailed maritime information, including temperature, salinity, turbidity, oxygen levels as well as the intensity and direction of currents,” scientists Yu Jiancheng told Chinese state media service Xinhua.

But their capabilities — particularly in disputed waters — also have military intelligence applications.

“The data is being transmitted back to a land-based laboratory in real time,” the expedition’s chief scientist told Chinese state media service Xinhua. The submersible drones are also virtually silent.

Both are capabilities the United States has been struggling to attain, Newsweek reports.

In December last year, a Chinese naval vessel siezed a US underwater research drone being operated in waters claimed by both Beijing and the Philippines, near Scarborough Shoal.

If being used as silent underwater eyes, such drones would be able to observe the movements of ships above, and possibly even submarines.

It’s a fast and quiet surveillance capability in the hotly contested South China Sea that could give Beijing’s military an edge, enabling its new combat-jet and missile-armed artificial island fortresses the ability to act faster than anticipated.

Earlier this week, Beijing again threatened ‘stern counteractions’ against any move to challenge its self-declared soverignty over the heavily travelled waterway between Vietnam, the Philippines and Malaysia.

“If the US military continues FONOPs near China’s islands in the name of freedom of navigation, this will only impede peace and stability in the South China Sea. Countries having disputes with China in the waters are likely to consider these US moves as supportive and hence take risky actions to challenge China’s sovereignty and maritime claims,” an article posted in the Global Times earlier this week reads. “This will meet stern counteractions from China.”

China has been rapidly advancing drone technology over recent years. Now it’s regarded a world leader.

China’s Academy of Sciences reportedly tested the Haiyi at a depth of just over 6km. This is significantly deeper than the previous record set by the US.

In 2014, an earlier model was reportedly capable of travelling over 1000km in 30 days.

Beijing boasts the new Haiyi sea gliders represent a significant upgrade over this, with reduced energy consumption and better efficiency resulting in greater endurance.

Another sea-skimming drone was unveiled earlier this year, skipping across the surface with just centimetres of clearance. It can reportedly cover 1500km at about 1000km/h.