Cyber & technology, explained.
Fibre-optic internet cables onboard the "Sophie Germain" cable boat of "Orange Marine" in La Seyne-sur-Marne harbour, France (Miguel Medina/AFP via Getty Images)
Cable owners want light-touch rules on sensing – but in the Indo-Pacific, barely any rules exist to touch.
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Fibre sensing: how undersea cables learned to listenFibre sensing: how undersea cables learned to listen
Submarine telecommunications cables are under intense government scrutiny, morphing from largely invisible digital plumbing to objects of keen security interest. Governments are creating strategies, militaries are running exercises and elected officials are asking thorny questions. The cables carrying more than 99% of the world’s international internet traffic are now firmly on the agenda of foreign ministries and defence departments across the Indo-Pacific.
But a quieter shift is happening in parallel – one that is reshaping the fundamental nature of these submarine cable systems.
These glass threads on the seabed are no longer merely passive conduits for data to traverse. They can now listen to the underwater environment.
The enabler is a family of technologies known as fibre-optic sensing (Opens in new window) (fibre sensing). Rather than adding discrete instruments to a cable’s repeaters, fibre sensing turns the optical fibre itself into a sensor – using the same glass thread that carries data to sense changes in its surrounding environment. Distributed Acoustic Sensing (Opens in new window) (DAS) uses the backscatter of laser pulses to detect acoustic signals, though on long-haul cables its reach typically ends at the first repeater. Monitoring shifts in the state of polarisation (Opens in new window) enables detection of underwater events. Together with related techniques such as distributed temperature sensing (Opens in new window) and optical interferometry, fibre sensing is transforming submarine cable networks from passive infrastructure into active observers of the ocean and what moves through it.
A parallel development – Science Monitoring and Reliable Telecommunications (SMART) cables (Opens in new window) – embeds equipment including seismometers, pressure gauges and temperature sensors, into cable repeaters, which otherwise boost a network’s signal and are located approximately every 100 kilometres. Fibre sensing and SMART systems differ technically but both can transform a submarine cable network from a bit-transmitting conduit into a sophisticated underwater sensing array.
Whether or not an operator chooses to provide data to governments, the perception that civilian submarine cable infrastructure is performing underwater surveillance functions carries distinct consequences.
For the cable industry, fibre sensing technologies are good for network resilience. Many cable faults are caused by errant fishing gear and dragged anchors, and sensing offers operators a means to spot patterns of negligent vessel behaviour, warn ships’ masters before damage occurs, and gather evidence should a cable be fouled. Moreover, these sensors can flag a cable that has become exposed (since being buried during installation, for example), identify abrasion, or detect a developing issue before a fault occurs. Cable owners can plan maintenance more efficiently, reduce downtime, and lower the cost of operating networks in remote waters.
The civilian co-benefits are also considerable. The same techniques that can sense a passing trawler can detect an earthquake, a tsunami, or the calls of migrating whales. Cabled sensing networks promise dense, real-time observation of oceans that are still remarkably unknown – with implications for climate science, disaster early warning, and the management of marine protected areas. These systems can improve fisheries enforcement, environmental compliance, and search-and-rescue, which can be better implemented with improved awareness of what is moving on and below the ocean’s surface.
This is why the International Cable Protection Committee (ICPC), in a February 2026 “Viewpoint” on fibre sensing (Opens in new window), urged governments to exercise restraint in regulating cable sensing. Heavy-handed rules, the ICPC argued, risk stifling a technology whose value to ocean science and infrastructure protection is hard to quantify. Cable owners, it asserted, should not be obliged to pass sensing data to governments, and sensing that serves cable protection should be treated as an exercise of cable freedoms under the UN Convention on the Law of the Sea, not as “marine scientific research” which would require coastal state consent.
Fibre sensing’s dual-use character is intrinsic to the technology (Kyler Chatman/DVIDS)
The ICPC’s position is reasonable on its own terms as premature regulation could indeed slow a technology which may have real and broad benefits. But the call for restraint presumes there is something to restrain. Across most of the Indo-Pacific, there is not. Comprehensive submarine cable regulation is thin, and rules tuned specifically to sensing are nascent.
That gap matters because fibre sensing’s dual-use character is intrinsic to the technology. While distributed acoustic sensing can detect a trawler, it can also detect a submarine. State of polarisation monitoring can register an anchor strike, and it can register the passage of a warship. Whether or not an operator chooses to provide data to governments, the perception that civilian submarine cable infrastructure is performing underwater surveillance functions carries distinct consequences. Among them are questions about how such infrastructure would be treated in a crisis or conflict, and how UNCLOS applies to cable networks that both carry data and collect it.
Various stakeholders have legitimate concerns here, and they are not currently in productive dialogue. Cable owners and operators may want to deploy sensing for network resilience purposes. Coastal states have reasonable interests in knowing what is being sensed in their maritime zones, and by whom. Militaries, on multiple sides, are exploring how cable-based sensing can contribute to underwater domain awareness. Scientists want access to the ocean data these systems generate.
None of these interests is unreasonable, and none of them, taken alone, will determine how this technology should be deployed and governed. But governments will not wait for a consensus. A range of state responses is coming, and each will complicate how cable networks are built, operated and repaired. The ICPC’s call for restraint may soon look like a luxury.
This article was written as part of a multi-year project being undertaken on Defending Seabed Critical Infrastructure (Opens in new window) by the Australia India Institute (Opens in new window), University of Melbourne, with the support of the Australian Department of Defence.
About the authors
Samuel Bashfield
Samuel Bashfield is research fellow at La Trobe University’s Centre for Global Security.
Oscar Youlten
Oscar Youlten is a Senior Consultant at Eolas Solutions, a Canberra-based defence consulting firm.
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