China’s testing of giant uncrewed underwater drones marks a potentially transformative moment in maritime warfare, shifting attention away from aircraft carriers and missiles toward the largely unseen battlespace beneath the waves.
According to reporting by Naval News, China is testing at least two models of extra-extra-large uncrewed underwater vehicles (XXLUUVs) in the South China Sea. These systems, comparable in size to conventional submarines, are believed to be diesel-electric platforms capable of carrying torpedoes, sea mines, and smaller underwater vehicles. Analysts assessing satellite imagery and open-source data say the drones could have operational ranges approaching 18,500 kilometers, a figure that would allow them to traverse entire ocean basins without human crews.
The development work appears to be taking place at a relatively obscure Chinese naval facility, suggesting a deliberate effort to shield the program from scrutiny. While China has previously showcased experimental vessels at public shipyards, analysts note that the concealment surrounding these tests, combined with evidence of two distinct designs, points to a competitive procurement effort rather than mere research and development. In other words, the People’s Liberation Army Navy (PLAN) may already be thinking in terms of deployment, not experimentation.
Technically, the drones’ reported combination of large battery banks and onboard diesel generators would allow extended submerged operations, punctuated by periodic recharging. That design could enable the vehicles to slip through anti-submarine warfare barriers across the Pacific, exploiting gaps in surveillance coverage and reducing the risks associated with crewed submarines operating far from home waters.
At the tactical level, such platforms could be used for minelaying or interdiction missions near contested chokepoints. Their extreme range, however, suggests ambitions far beyond coastal defense. Analysts argue that XXLUUVs could give China the ability to threaten ports along the US West Coast, interfere with maritime traffic, or apply pressure at strategic hubs such as the Panama Canal in the event of a major conflict.
One of the most consequential implications lies in the vulnerability of undersea infrastructure. Modern economies and militaries depend heavily on submarine fiber-optic cables, which carry the vast majority of global data traffic. China’s large uncrewed underwater vehicles could be well suited to targeting these cables, either during a conflict over Taiwan or as part of broader efforts to paralyze an adversary’s command, control, and economic systems.
Taiwan is particularly exposed. In a June 2025 article for the Global Taiwan Institute, analysts Jaime Ocon and Jonathan Wahlberg noted that the island relies on just 24 undersea cables for international connectivity. Severing even a portion of these links could disrupt banking, emergency services, and government communications, amplifying the effects of a blockade without the immediate use of kinetic force. Such actions could form part of an all-domain pressure campaign designed to coerce Taipei while complicating foreign intervention.
The threat is not limited to Taiwan. Writing for the Small Wars Journal in May 2025, Andrew Rowlander highlighted the vulnerability of the Trans-Pacific Cable network linking Japan, Guam, and Hawaii. The sheer scale of the Pacific Ocean provides ample cover for covert sabotage operations. An attack on these cables could deal a severe blow to regional economies and significantly degrade US military command and control across the Indo-Pacific.
China’s progress in deep-sea technology adds weight to these concerns. In March 2025, the South China Morning Post reported that Chinese researchers had developed a cable-cutting tool capable of operating at depths of up to 4,000 meters. Mounted on a robotic arm and using a diamond-coated grinding wheel, the device is designed to slice through armored cables while minimizing sediment disturbance—an attribute well suited to covert operations. Integrated into a large uncrewed underwater vehicle, such tools could enable systematic attacks on critical infrastructure.
Beyond cables, XXLUUVs could be used to neutralize undersea sensor networks. The United States and its allies operate extensive arrays of underwater sensors, including the so-called “Fish Hook” network stretching from Japan through Taiwan and the Philippines into Southeast Asia. These systems are intended to detect Chinese submarines attempting to break out from the First Island Chain. Analysts suggest that uncrewed underwater drones could plant explosives or sever sensor cables ahead of a major naval push, easing the path for PLAN surface ships and submarines into the open Pacific.
Such a breakout would have strategic implications, particularly for China’s nuclear deterrent. Gaining access to deeper waters could allow its Type 094 ballistic missile submarines to conduct more survivable patrols, reducing reliance on a South China Sea bastion strategy and complicating US and allied tracking efforts.
China’s ambitions may extend even further. Past deployments of smaller unmanned underwater vehicles in the Indian Ocean, reported by Janes in 2020, demonstrated Beijing’s interest in mapping and understanding distant maritime environments. A more capable XXLUUV could support longer missions, collect higher-quality data, and operate across a wider range of tasks, from reconnaissance to infrastructure interference.
This raises concerns for India, particularly if China seeks to secure alternative sea lines of communication bypassing the Malacca Strait through ports such as Kyaukpyu in Myanmar. Indian naval analysts have warned that the spread of Chinese-made submarines and support facilities across the region could eventually enable sustained PLAN operations in the Indian Ocean, reshaping the regional balance.
Some observers have speculated about an even darker possibility: the use of large underwater drones as nuclear delivery systems, conceptually similar to Russia’s Poseidon. Yet most analysts see limited strategic value in such an approach. Uncrewed underwater vehicles are slow, largely confined to coastal targets, and ill-suited to managing escalation in fast-moving nuclear crises. China already possesses faster and more flexible options, including intercontinental ballistic missiles.
In this light, China’s XXLUUVs appear less like doomsday weapons and more like tools of coercion and disruption. By threatening cables, sensors, and distant ports, they underscore how the next major maritime contest may hinge not on visible fleets, but on silent machines operating far below the surface.
