Silent Seas: Why Sri Lanka Must Build an Underwater Acoustic Shield Around Its Island
By Maritime Security Correspondent
The Indian Ocean has long been portrayed as a tranquil expanse of blue surrounding the teardrop-shaped island of Sri Lanka. Yet beneath those waters, far beyond the sight of fishermen and commercial shipping, an invisible contest of steel and sonar is intensifying. Submarines from major powers now move through the region with increasing frequency, turning what once seemed distant geopolitical manoeuvres into immediate maritime security concerns for Colombo.
The alleged torpedo attack on the Iranian frigate IRIS Dena on 4 March 2026, reportedly around 40 nautical miles south of Sri Lanka’s Galle Port, has reignited debate within naval circles about a vulnerability long discussed but rarely addressed: Sri Lanka’s inability to detect underwater threats moving through its surrounding seas.
Naval analysts now argue that the island nation urgently needs to establish a network of underwater acoustic sensors—a seabed-based listening system capable of detecting submarine movements within a wide perimeter, potentially extending up to 200 nautical miles around the island.
Such a system, experts say, would transform Sri Lanka from a passive observer into an active maritime surveillance state.
The Silent Domain Beneath the Waves
Submarines represent one of the most difficult military assets to detect. Modern nuclear and diesel-electric submarines are engineered to operate with near silence, often travelling hundreds of kilometres undetected.
The suspected involvement of a USS Minnesota in the strike against the Iranian warship illustrates the evolving realities of submarine warfare in the Indian Ocean. While such incidents remain rare, they underscore how conflicts between distant powers can suddenly unfold near smaller coastal states.
For Sri Lanka, located along the world’s busiest east–west shipping lanes, the risk is not theoretical.
More than 60,000 merchant vessels pass near Sri Lankan waters annually, including oil tankers, container ships and bulk carriers linking Asia, Europe and the Middle East. Any military confrontation occurring within this maritime corridor could threaten both global trade and Sri Lanka’s own economic lifelines.
The attack on the Iranian vessel—reportedly resulting in the loss of over a hundred sailors—demonstrates the devastating consequences when submarines operate without detection.
The Case for an Underwater Acoustic Sensor Network
Naval strategists are therefore calling for the establishment of a seabed acoustic monitoring network, essentially an underwater equivalent of radar.
Unlike surface surveillance systems, acoustic sensors detect sound signatures produced by submarines. Propellers, engines and hull vibrations generate distinct acoustic fingerprints that can be captured by hydrophones placed along the seabed and connected through fibre-optic cables.
These systems function continuously and silently, feeding data into shore-based naval command centres.
The concept is not new.
The United States pioneered similar systems during the Cold War through the Sound Surveillance System, known widely as SOSUS, which allowed the U.S. Navy to track Soviet submarines across vast ocean regions.
For Sri Lanka, however, the strategic objective would differ. Rather than monitoring global submarine fleets, Colombo’s goal would be to establish maritime situational awareness around its territorial waters and Exclusive Economic Zone (EEZ).
A sensor network stretching up to 200 nautical miles could create a defensive acoustic ring around the island.
Protecting Strategic Maritime Assets
Sri Lanka’s maritime domain is far more valuable than commonly assumed.
Beyond commercial shipping routes, the island sits near important undersea resources, including potential mineral deposits within the Indian Ocean seabed. Some geological surveys suggest the presence of cobalt-rich crusts and polymetallic nodules in nearby seamounts.
Equally critical are Sri Lanka’s maritime infrastructure and naval assets.
The Port of Colombo, one of South Asia’s busiest container ports, handles millions of containers annually. Any security threat within surrounding waters could disrupt shipping routes and insurance markets.
Sri Lanka also operates major naval bases, including SLNS Dockyard and facilities along the southern coast. Without effective underwater monitoring, these installations remain exposed to covert submarine movements.
The acoustic network being proposed would therefore serve multiple purposes:
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Monitoring submarine activity near commercial shipping routes
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Protecting naval bases and maritime infrastructure
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Detecting underwater intrusions near offshore resources
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Supporting maritime domain awareness for the Sri Lankan Navy
Learning From Regional Powers
Sri Lanka would not be alone in adopting such technology.
China has spent years constructing a sophisticated underwater monitoring network across the South China Sea. Analysts often describe this network as part of the country’s broader maritime surveillance architecture sometimes referred to as the “Great Underwater Wall.”
The system combines seabed sensors, underwater drones and satellite communications to monitor submarine activity within contested waters.
Similarly, Pakistan has invested in underwater detection technologies to secure its coastline along the Arabian Sea.
Regional security sources also suggest that Bangladesh has explored similar capabilities to monitor submarine activity within the Bay of Bengal, potentially with external technical support.
These developments highlight a growing reality: underwater surveillance is becoming a standard feature of maritime security, not an optional luxury.
A Cost-Effective Defence Strategy
Compared with purchasing additional warships or submarines, seabed acoustic systems can be relatively economical.
The primary infrastructure involves:
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Hydrophone arrays placed along strategic seabed locations
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Fibre-optic cables transmitting acoustic data to shore
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Signal processing centres operated by naval analysts
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Integration with radar and satellite surveillance
Once installed, such systems can operate for years with minimal maintenance.
Naval analysts argue that Sri Lanka could deploy the network in phases, initially focusing on strategic corridors south of the island where most submarine transit routes pass between the Arabian Sea and the Pacific.
The network could later expand toward the eastern and western maritime boundaries.
International cooperation could also play a role. Maritime partners interested in securing Indian Ocean sea lanes might support technical development, training or funding.
A Strategic Wake-Up Call
For many observers, the suspected submarine strike near Sri Lanka’s waters serves as a warning.
The island sits at the crossroads of great-power naval activity. Warships from the United States, China, India and other powers regularly transit nearby sea lanes. Submarines, by their nature, remain unseen.
Without acoustic monitoring, Sri Lanka effectively operates blind in the underwater domain.
The tragic fate of the Iranian frigate demonstrates how quickly events beneath the waves can escalate.
While submarine warfare rarely occurs near small island states, the consequences of even a single incident can be catastrophic—whether for naval personnel, commercial shipping or regional stability.
Building the Island’s Underwater Shield
If Sri Lanka proceeds with an acoustic monitoring system, it would represent one of the most significant developments in the island’s maritime defence strategy since the end of its civil war.
Such a system would not turn Sri Lanka into a naval superpower. But it would provide something equally valuable: awareness.
In modern naval doctrine, awareness often determines survival.
By detecting submarine movements early, Sri Lanka could alert commercial vessels, coordinate with friendly navies and prevent hostile activity within its maritime zone.
The ocean surrounding the island may appear calm on the surface.
But beneath those waters, the silent world of submarines continues to expand. For Sri Lanka, the lesson from recent events is clear: the nation must begin listening to the sea.