China's warships face a threat they may struggle to detect: What a new study reveals

China is rapidly expanding its aircraft carrier fleet as it seeks to strengthen its global naval presence, but its massive warships could remain vulnerable to one major threat—submarine attacks.

A recent report by the Washington-based Centre for Strategic and International Studies (CSIS) outlined a "cost-imposition" strategy through which the US and its allies could threaten China's aircraft carriers.

The strategy includes land-based strike networks, long-range air strikes supported by satellites, cyber and electromagnetic attacks, drone swarms and submarine ambushes.

According to a South China Morning Post report citing the CSIS study, the last of these could exploit a key weakness in the People's Liberation Army Navy's (PLAN) capabilities.

The study identified US attack submarines operating in the western Pacific as a potent threat to Chinese carrier groups, arguing that gaps in China's ability to detect and track undersea threats could leave its high-value warships exposed.

China currently operates three aircraft carriers—the Liaoning, Shandong and Fujian—all of which are conventionally powered.

The Liaoning, a refitted Soviet-era vessel, was commissioned in 2012, followed by the indigenously built Shandong in 2019. China commissioned its third and largest carrier, the Fujian, last November at a ceremony attended by President Xi Jinping.

With a full-load displacement exceeding 80,000 tonnes, the Fujian is equipped with an electromagnetic aircraft launch system (EMALS), making it the world's second aircraft carrier to use electromagnetic catapults after the US Navy's USS Gerald R Ford.

Aircraft including the J-15T, J-35 and KJ-600 have successfully completed catapult-assisted take-offs and arrested landing training aboard the Fujian, according to China's Defence Ministry.

Why submarines could pose a major threat

The CSIS report says submarines could threaten Chinese carrier groups as they move through strategic waterways. Farther out at sea, carrier-based aircraft could also target them, aided by satellite surveillance and targeting, while attacks on sensors and communications could disrupt Chinese naval operations.

Christopher Sharman, director of the China Maritime Studies Institute at the US Naval War College, told the SCMP that China's undersea vulnerability "remains significant today", although it was "not a static weakness".

The PLAN has invested heavily in improving its understanding of the undersea operating environment. However, Sharman said important gaps remain, with PLAN-affiliated authors themselves acknowledging that China's meteorological and oceanographic capabilities continue to lag those of the US Navy.

"This comparative lack of knowledge about the undersea ocean battlespace remains an impediment to PLAN submarine and anti-submarine warfare operations, particularly beyond the first island chain," Sharman said.

Timothy Heath, head of defence research firm Perceptum, similarly said anti-submarine warfare remained a challenge for China, particularly because US submarines are among the world's quietest.

Carriers more vulnerable farther from China

The challenge could become greater as Chinese carriers operate farther from the mainland.

Heath warned against deploying the carriers too far from China's shores because of the multiple ways in which the US could target them.

"The carrier is too valuable and costly to deploy in such a vulnerable way," he said, arguing that China's land-based intermediate-range ballistic missiles remain its best option for threatening US ships out to the second island chain.

Japanese intervention in a potential conflict over Taiwan could further complicate matters, Heath said, as Japan could seek to target Chinese warships operating near its coast.

The CSIS report argued that the difficulties China faces in protecting its carriers farther from home should influence US procurement decisions, calling for greater investment in torpedoes, undersea drones and missile production alongside allies including Japan and Australia.

For China, therefore, building more aircraft carriers is only part of the challenge. As its naval ambitions expand farther from its shores, its ability to protect these valuable warships from submarines will also have to keep pace.