Chinese Underwater Drones Found in Philippine Waters Raise Maritime Security Alarms

Over the past several years, Filipino fishermen have recovered multiple Chinese-origin underwater unmanned vehicles (UUVs) adrift or grounded in Philippine territorial waters. These discoveries—often unannounced by Beijing—highlight an expanding pattern of covert undersea intelligence-gathering operations by the People’s Liberation Army Navy (PLAN) across the South China Sea. The frequency and locations of these recoveries raise significant questions about China’s seabed warfare capabilities and long-term strategic intentions in the region.

Pattern of Discovery: Recovered UUVs Across Philippine Waters

Since at least 2016, Filipino fishermen and local authorities have reported finding torpedo-shaped unmanned underwater vehicles (UUVs) near Palawan, Mindoro Strait, and other areas adjacent to contested maritime zones. The most recent incident occurred in early 2025 when a group of fishermen off the coast of Occidental Mindoro retrieved a 1.5-meter-long cylindrical object bearing Chinese markings and what appeared to be sensor apertures.

Previous incidents include:

December 2019: A Chinese UUV was found floating off the coast of Tawi-Tawi province. It was later identified as a Sea Wing (Haiyi) glider used for oceanographic data collection.
March 2021: Another glider was recovered near Mindoro Strait with similar characteristics—no propulsion system but equipped with fins for buoyancy-driven movement.
July 2023: Fishermen near Palawan found a more advanced variant with what appeared to be side-scan sonar modules.

The Philippine Navy has confirmed that these devices are consistent with Chinese ocean gliders used for hydrographic data collection. However, defense analysts note that such data is dual-use—supporting both civilian research and military applications like submarine navigation or anti-submarine warfare (ASW).

The Haiyi Glider: A Dual-Use Oceanographic Platform

The majority of recovered systems appear to be variants of the Haiyi (“Sea Wing”) underwater glider developed by the Shenyang Institute of Automation under the Chinese Academy of Sciences (CAS). These battery-powered platforms use variable buoyancy to glide through water without propellers or active noise signatures—making them ideal for stealthy long-duration missions.

Key features include:

Length: ~1.5–2 meters
Endurance: Up to several months depending on mission profile
Sensors: CTD sensors (conductivity-temperature-depth), turbidity meters, ADCPs (Acoustic Doppler Current Profilers), and increasingly EO/IR or sonar payloads

The Haiyi series has been deployed extensively by China’s State Oceanic Administration since at least 2014 for scientific surveys—but its proliferation into disputed maritime zones suggests strategic ISR utility. In particular, bathymetric mapping assists PLAN submarines in navigating complex littoral environments while evading detection.

Tactical Implications: Seabed Warfare and Submarine Support

The presence of autonomous gliders in key chokepoints like the Mindoro Strait or near Palawan indicates more than passive surveillance—it suggests preparation for future undersea dominance. Hydrographic data collected by these UUVs can support:

Cable mapping / sabotage planning
Minesweeping / minelaying route optimization
Synthetic aperture sonar calibration for manned submarines
C3I relay planning using seabed nodes or UUV swarms

This aligns with China’s broader “Intelligentized Warfare” doctrine emphasizing AI-enabled autonomy across all domains—including subsea operations. The PLAN’s increasing investment in underwater robotics also dovetails with its ambitions to control first-island-chain access routes via asymmetric means.

Lack of Transparency from Beijing Raises Regional Alarm

No official explanation has been provided by China regarding any of these recoveries—even when serial numbers or institutional markings were visible on the devices. This contrasts sharply with international norms where lost oceanographic equipment is typically claimed via diplomatic channels or scientific registries like IOC-UNESCO’s Global Ocean Observing System (GOOS).

The opacity surrounding these deployments undermines trust among ASEAN neighbors and reinforces perceptions that Beijing is using civilian cover to mask military activities—a tactic seen previously with fishing militia vessels and survey ships operating under nominally non-military auspices.

Philippine Response and Regional Maritime Domain Awareness Gaps

The Armed Forces of the Philippines (AFP) has limited capacity to detect or interdict low-signature UUVs operating below periscope depth. While surface radar coverage has improved via coastal radar networks funded partly through U.S.-Philippine cooperation programs like EDCA (Enhanced Defense Cooperation Agreement), subsurface domain awareness remains minimal outside major naval bases.

This vulnerability underscores a broader challenge across Southeast Asia: most regional navies lack robust anti-UUV capabilities or integrated undersea surveillance networks akin to NATO’s SOSUS/IONA systems. Efforts are underway—including Japan’s assistance to Vietnam’s maritime security—but progress is uneven.

A Growing Trend Across Indo-Pacific Waters?

The Philippines is not alone in encountering unexplained Chinese UUV activity:

Indonesia (2020): A Haiyi-type glider was found off Sulawesi Island; Indonesian Navy expressed concern over unauthorized data gathering.
Sri Lanka (2021): Reports emerged that an unidentified submerged object matching Chinese design washed ashore during monsoon season.
Taiwan Strait & East China Sea: Japanese analysts have tracked suspected autonomous gliders moving along known PLAN submarine transit corridors.

A Call for Multinational Undersea Surveillance Cooperation

The increasing prevalence of stealthy unmanned systems beneath contested waters demands new frameworks for transparency and monitoring. Potential steps include:

Bilateral agreements on lost equipment notification protocols between claimant states
NATO-style regional acoustic sensor sharing initiatives among ASEAN+ partners
Crowdsourced reporting platforms leveraging commercial fishing fleets’ observations via satellite-linked apps or radios

A Strategic Indicator Worth Watching Closely

The repeated recovery of Chinese underwater drones around Philippine waters is not merely an anomaly—it reflects a deliberate effort by Beijing to shape undersea battlespace conditions before conflict arises. As great power competition extends into seabed terrain mapping and persistent ISR coverage beneath contested seas, unmanned systems will play an increasingly central role in shaping deterrence dynamics—and possibly escalation thresholds—in maritime Asia.