China’s testing of giant un-crewed underwater drones signals a quiet but consequential shift in maritime warfare, one that could threaten undersea cables, sensor networks and even the strategic balance across the Pacific and Indian Oceans.
This month, Naval News reported that China is testing two new models of extra‑extra‑large uncrewed underwater vehicles (XXLUUVs) in the South China Sea, systems that analysts say could give it the ability to threaten ports on the US West Coast in the event of conflict. The drones, comparable in size to conventional submarines, are believed to be diesel‑electric and capable of carrying torpedoes, sea mines, and smaller underwater vehicles.
The platforms, assessed to have operational ranges of roughly 18,520 kilometers, are being developed in secrecy at an obscure Chinese naval facility, according to open‑source analysis. Their design incorporates large battery banks and diesel generators, enabling extended submerged transit and potentially allowing them to slip through anti‑submarine defenses across the Pacific.
China’s shipyards have previously showcased experimental vessels. Still, analysts say the scale of production, the concealment of testing, and the existence of two competing XXLUUV designs indicate a competitive procurement program rather than research trials.
The drones could be used for minelaying or interdiction missions in tightly defined zones. Still, their long range suggests a strategic purpose: enabling China to project pressure far beyond East Asia, including potential blockades of US West Coast ports or the Panama Canal. Analysts say the systems may complement China’s emerging crewed submarines as PLAN seeks to expand its reach in the Pacific.
Aside from carrying mines, torpedoes or smaller underwater vehicles, China could use its XXLUUVs to attack critical undersea cables as part of a Taiwan blockade or to paralyze the US military.
Taiwan is highly susceptible to such an attack, as Jaime Ocon and Jonathan Wahlberg point out in a June 2025 article for the Global Taiwan Institute (GTI), which states that the self-governing island depends on only 24 undersea cables for internet access. Ocon and Wahlberg note that severing these cables could throw everything from banking to emergency services into disarray. Severing Taiwan’s undersea cables could form part of an all-domain blockade by China, starving the the island of energy, food supplies, information, and depriving it of critical services, to force capitulation without firing a shot.
Beyond Taiwan, Andrew Rowlander, in a May 2025 article for the Small Wars Journal (SWJ), points out the vulnerability of the Trans-Pacific Cable (TPC) – a series of underwater cable networks linking Japan Guam, and Hawaii, with the vastness of the Pacific useful for hiding sabotage operations. A sabotage attack against the TPC could devastate the economies of Japan, Guam, and Hawaii, and significantly degrade US military command and control in the Pacific.
The modular nature of XXLUUVs could mean they could be equipped for cutting thick, armored undersea cables. In March 2025, the South China Morning Post (SCMP) reported that China had developed a tool for cutting such cables, which, when deployed from a submersible, could operate at a depth of 4,000 meters. SCMP notes that the tool, mounted on a robotic arm, uses a diamond-coated grinding wheel spinning at 1,600 rounds per minute to shatter steel while minimizing marine sediment disturbance.
Island chain strategy. Map: ResearchGate
Beyond attacking undersea cables, China’s XXLUUVs could be used to attack US undersea sensor infrastructure in preparation for a naval breakout beyond the First Island Chain.
Notably, the US operates the “Fish Hook” underwater sensor network spanning Japan, Taiwan, the Philippines, and the Java Sea.
It is designed to detect Chinese submarines trying to break out from the First Island Chain.
China’s XXLUUVs may be used to neutralize those sensors by planting explosive charges on them or severing their cables before attempting a naval breakout into the open Pacific. A breakout by surface and submarine forces may be necessary to blockade Taiwan, interdict intervening US and allied forces, and enable open-ocean deterrent patrols by its Type 094 nuclear ballistic missile submarines (SSBNs) – freeing its undersea nuclear deterrent from the constraints of a bastion strategy confined to the South China Sea.
These XXLUUVs could also extend China’s reach beyond the Pacific – specifically, into the Indian Ocean. To illustrate, Janes in March 2020 reported that China has deployed unmanned underwater vehicles (UUVs) in the Indian Ocean, specifically 12 Sea Wing underwater gliders that completed a hydrographic mission spanning 550 days and 12,000 kilometers.
A more capable XXLUUV could enable longer mission durations, cover greater distances, and support more types of missions. Such missions may gather crucial data for future Chinese submarine operations in the region. If the Malacca Strait—where all of China’s key sea lines of communication (SLOCs) converge and through which two-thirds of its trade and 83% of its oil imports pass—gets blockaded in a Taiwan or South China Sea contingency, China might need to find alternative routes through the Indian Ocean.
Specifically, this could involve utilizing the China-funded deepwater port at Kyaukpyu in Myanmar to bypass the Malacca Strait. However, China securing its Indian Ocean SLOCs and Kyaukpyu might put it up against India. In turn, India might be concerned about strategic encirclement from China and its partners, Myanmar, Pakistan and Bangladesh.
Indian Navy Rear Admiral Monty Khanna states in an August 2024 Proceedings article that the spread of Chinese-made submarines and their support infrastructure in the Indian Ocean by regional countries such as Myanmar, Pakista, and Bangladesh could eventually enable China’s submarines to conduct missions in the Indian Ocean.
Besides neutralizing undersea cables and sensors and expanding China’s reach into the Indian Ocean, its XXLUUVs could theoretically serve as an alternative nuclear delivery system designed to bypass US missile defenses by approaching targets from underwater, echoing the logic behind Russia’s nuclear-powered Poseidon system.
Yet this concept offers limited strategic value. While an undersea route circumvents missile defenses, such systems are far slower than ballistic missiles. They are restricted mainly to coastal targets, and poorly suited to time-sensitive escalation control.
China already possesses faster, more flexible nuclear options—such as the DF-41 ICBM, which can reportedly reach the US mainland in roughly 30 minutes. In contrast, a large XXLUUV launched from Chinese waters could take days or even weeks to arrive, potentially detonating long after an initial nuclear exchange had concluded.
This limitation can relegate nuclear-armed underwater drones to a deep second or third-strike “insurance” role rather than a usable deterrent or escalation tool, offering revenge rather than leverage in a high-end conflict.
