China’s newest and most advanced aircraft carrier, the Fujian, has recently drawn global attention — not for its massive flight deck or electromagnetic catapult system, but for a defensive upgrade hidden beneath the waterline. According to reports from the South China Morning Post, the warship has removed its older depth-charge launchers and installed a set of six rotating 324-millimeter tubes. Naval analysts identify this as an Anti-Torpedo Torpedo (ATT) system: a “hard-kill” defense designed to detect, track, and destroy incoming underwater weapons before they strike the hull.

If confirmed, the Fujian would be the first active-service aircraft carrier in the world to carry a dedicated underwater terminal defense array of this kind. Powered by a permanent magnet synchronous direct-drive motor and pump-jet propulsion, the interceptor is said to accelerate to speeds of 50 to 60 knots in just three seconds. Notably, this is technology the U.S. Navy tested for more than five years before abandoning it in 2018, citing issues with reliability, detection accuracy, and inconsistent performance across different water conditions. For open-ocean operations, this system would be a major strategic asset — but in the Visayan Sea, it becomes almost entirely irrelevant.

1. The Visayan Sea: Not As Open As It Looks

On standard navigation maps, the Visayan Sea appears as a broad expanse of blue water connecting the major island groups of the central Philippines. But oceanographic surveys by the Philippine Bureau of Fisheries and Aquatic Resources, the National Mapping and Resource Information Authority (NAMRIA), and international research institutions tell a very different story. The entire basin averages just 40 meters in depth, with large areas shallowing to only 20–30 meters between islands, reefs, and shifting sandbars.

It is not just shallow — it is geographically confined. The sea is bounded by Panay, Negros, Cebu, Leyte, and Masbate, and linked to surrounding waters only through narrow passages: San Bernardino Strait to the north, Surigao Strait to the southeast, and the Tañon, Guimaras, and Verde Island passages to the south and west. So complex is this topography that global ocean circulation models cannot even accurately resolve its currents, temperature layers, or sound propagation patterns.

Forty meters is more than enough water to float even the largest warship — the Fujian displaces around 80,000 tons and draws roughly 11 meters when fully loaded — but it leaves almost no room for error, and even less room for the kind of maneuvering and sensing modern warships rely on during combat.

Strategic Connections: Ports and Coastal Waters

This shallow profile defines the entire operational environment around key economic and security hubs, including Roxas City, Estancia, Concepcion, and Cadiz City:

• Roxas City and the Port of Culasi: Serving as the main gateway to northern Panay, its approach channel measures only 4.9 meters deep, with maximum anchorage depths reaching just 6 to 7 meters. Large deep-draft vessels cannot come alongside; they must anchor several kilometers offshore and transfer cargo and passengers through smaller barges. For warships, this means no safe berthing or protection from sudden weather changes.
• Estancia and Concepcion: Located on the northeastern coast of Iloilo, these towns sit right in the heart of the Visayan Sea’s shallowest zone. Surrounded by the Gigantes Islands and extensive coral reef systems, depths here rarely exceed 25 to 35 meters, while inner passages and sheltered coves drop to only 3 to 5 meters. These waters are busy with thousands of fishing vessels daily, but they are effectively closed to any ship larger than a patrol boat.
• Cadiz City: On the northern coast of Negros Occidental, its port faces open Visayan waters but is ringed by wide sandflats and fringing reefs. The operational depth is limited to 5 to 6 meters, and the approach narrows sharply closer to shore. Even moderate-sized cargo ships must time their arrivals with high tide — a risk no naval commander would accept in a combat scenario.

All four locations highlight a simple geographic reality: this sea was formed for small boats, not capital ships.

2. The Hidden Limits of Big-Warship Warfare

The effectiveness of any warship is never measured by its size alone, but by how much of its capability it can actually use in a given environment. In the Visayan Sea, three critical advantages of large warships vanish almost entirely: draft and maneuverability, detection range, and weapons performance.

Draft and Turning Room

Draft — the vertical distance from the waterline to the lowest point of the hull — is the first limiting factor:

• Philippine Navy Miguel Malvar-class frigate: 3.7 meters draft
• U.S. Navy future FF(X) frigate: 6.7 meters draft
• Modern guided-missile destroyer: 7 to 9 meters draft
• Aircraft carrier: 11 meters or more draft, plus a required 2–3 meters of “under-keel clearance” to avoid grounding in rough or changing conditions.

Space to turn is equally vital. Naval architects specify that a carrier needs a safe turning radius of roughly 670 meters (2,200 feet) to change direction without straining its hull or propellers. Around Estancia, Concepcion, Roxas, or Cadiz, that radius would immediately cross into reefs, shoals, or populated coastlines.

Naval safety manuals also warn of stern squat: when a large ship slows down or reverses its engines in shallow water, water pressure beneath the hull drops, causing the stern to sink deeper and the bow to rise. This reduces rudder effectiveness and increases the risk of running aground — even if charts appear to show sufficient depth at first glance.

The Acoustic Disadvantage

Even if a large ship could navigate safely, its underwater sensors and defenses would struggle to function. In the open ocean, sound travels in stable layers for hundreds of kilometers, allowing long-range sonars to detect submarines and incoming torpedoes from great distances.

In shallow, enclosed waters, however, the physics change completely. Sound waves bounce repeatedly off the seabed and surface, creating bottom reverberation — a wall of noise that masks faint signals from underwater threats. The Visayan Sea is also one of the busiest inland waterways in Southeast Asia; between Roxas, Cadiz, Estancia, and Concepcion, thousands of fishing boats, ferries, and inter-island vessels operate daily, adding constant background noise that further confuses detection systems.

This is where the Fujian’s new system loses its purpose. It is designed to detect and engage a torpedo at ranges of 3 to 5 kilometers in deep water. In 40 meters of water, with so much interference, its effective detection range shrinks to just a few hundred meters — giving barely enough time to react, if it can distinguish the threat from surrounding noise at all.

3. The Right Tools for the Right Theater

These geographic realities are not new discoveries — they are the foundation of the Active Archipelagic Defense Strategy and the updated Comprehensive Archipelagic Defense Concept guiding the Philippine Navy today. The core principle is straightforward: big ships guard the gates; smaller ships secure the house.

For the Visayan Sea and the waters around Roxas, Estancia, Concepcion, and Cadiz, the advantage belongs to lighter, more agile platforms:

• Fast Attack Interdiction Craft and Missile Boats: With a draft of only 1.5 meters, these vessels can navigate waters as shallow as 2–3 meters. They can slip through narrow channels, hide behind landmasses such as the Gigantes Islands to create radar shadows, and launch missiles while using the terrain as natural cover. After firing, they can quickly reposition through passages no frigate would attempt to enter.
• Corvettes and Frigates: With drafts ranging from 3.7 to 6.7 meters, these ships act as the “eyes and ears” of the defense network. Instead of loitering in the shallowest zones, they patrol the deeper entry points: San Bernardino Strait to the north, Surigao Strait to the east, and the Guimaras and Tañon Straits to the south and west. From these deeper waters, they provide long-range radar coverage, air defense, and secure communications links to coordinate smaller craft operating inside.
• Destroyers and Aircraft Carriers: These high-value assets are best reserved for the open ocean — the West Philippine Sea, the Pacific Ocean east of the archipelago, and the Luzon Strait to the north. Here, depths reach thousands of meters, there is unlimited space to maneuver, and systems like the Fujian’s ATT defense can operate exactly as designed.

4. Regional Implications and Strategic Lesson

The development and installation of the Anti-Torpedo Torpedo system on the Fujian reveals a clear strategic concern: China is preparing its large surface fleet for combat in the deep waters of the Western Pacific, where it faces the greatest risk from advanced submarine forces. It is a response to the open-ocean duel, not to operations inside island chains.

For the Philippines and its neighbors, this highlights a broader truth about maritime security in Southeast Asia. With over 25,000 islands and vast areas of shallow, confined water, the region cannot rely on the same rules of engagement that apply to the Atlantic or central Pacific Oceans.

In the Visayan Sea, and specifically around key coastal communities and ports like Roxas, Estancia, Concepcion, and Cadiz, survival does not depend on intercepting a torpedo at the last second. It depends on not being detected in the first place. This is why the future of defense here will never be defined by tonnage, flight decks, or advanced underwater shields. Instead, it will be measured by shallow drafts, the ability to use islands as natural cover, and missiles that can strike effectively from hidden positions.

The Fujian’s new shield is a powerful capability — but only where the sea is deep enough to let it work. In the 40-meter waters of the Visayas, geography sets the terms of battle, and renders the world’s most advanced underwater defense system largely irrelevant.