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Scuba diver above ocean floor pipes

Reconsider Using Undersea Cables as Military Sensors

By Bronte Munro and Iain MacGillivray

The United States should think twice about the defense sensing potential of subsea cables.

Advancements in fiber optic technologies mean that subsea cables hold potential as undersea sensors that can detect tsunamis, earthquakes, marine life and, critically, naval vessels.

While the technology is still in its nascent stages, subsea fiber-optic cables have dual-use potential as sensors that could revolutionize naval defense intelligence, surveillance activities and serve as an early warning for the United States and its allies of unwanted foreign operations in the region.

Operationalizing dual-sensing technologies could hold significant potential for defense intelligence in the maritime domain. There are, however, potential risks that sensing technology poses to global economic and communication security, which require careful consideration.

Discussion regarding sensing capabilities for subsea cables is driven by the emergence of distributed acoustic sensing, or DAS, which is an innovative technique that relies on fiber optics to detect pressure waves emanating from acoustics of seismic activity. It requires the use of an unused fiber in the cable, known as a “dark” fiber. Light pulses are sent across the dark fiber using a specialized device called an interrogator.

Advanced signal processing can translate any fluctuations in the reflected light that the interrogator senses as it encounters defects along the fiber.

What makes the technology different to current oceanic sensing is that it doesn’t rely on discrete acoustic or seismic sensors placed along the seabed. Instead, it can potentially cover far greater distances by leveraging dark fibers in existing commercial subsea cables.

Distributed acoustic sensing has incredible potential in subsea defense activities by providing the ability to track both surface and subsurface targets. Whilst limited in range from between 30 to 60 miles at the current stage of development, the data could be effectively integrated into naval intelligence capabilities. From a practical standpoint, the use of dark fibers could impact the capacity of the subsea cables.

DAS sensing would likely be improved if an entire cable were dedicated to that purpose, as opposed to leveraging single dark fibers available in commercial cables. While the dual use aspect of the technology is still in its nascent stages, new commercial subsea cable infrastructure could eventually be leveraged for defense purposes.

Subsea cable development in the strategically important Indo-Pacific highlights the issues and risks due to the intersection of defense interests with critical commercial infrastructure development.

There are significant risks of compromising stability and eroding trust in commercial subsea cable providers if subsea cables increasingly become a point of tension in the strategic competition between China and the United States. Currently, subsea cable infrastructure accounts for 99 percent of global data traffic integral to internet, communication, financial and defense systems worldwide. Disrupting these for defense purposes could place subsea cable infrastructure at increased risk of sabotage by adversaries.

The United States has demonstrated success in routinely blocking Chinese companies — specifically HMN Tech, which has ties to Huawei and the Chinese government — from winning bids to build international cables. Currently, HMN Tech is expected to provide equipment for only 10 percent of existing and planned global cables. Three other cable suppliers — U.S.-owned SubCom and NEC and French-owned Alcatel Submarine Networks — account for approximately 90 percent of new subsea cable construction since 2017.

However, any question of commercial cables being used for defense sensing compromises the image of integrity that industry players have built, and the security and economic advantages this brings.

The market for subsea cables has almost doubled each year given the demand from content providers such as Google, Meta, Microsoft and Amazon, which rely on the cables to deliver their online and cloud services. Consequently, subsea cable industry resources are stretched thin.

As it stands, the subsea cable industry is currently reluctant to explore in depth the potential of sensing technology on commercial cables.

This reluctance is due to more pressing concerns regarding the costs of construction, availability of specialized resources including the 60 cable ships globally, waiting time for permits and costs of maintaining existing cables. The significant cost of laying subsea cables means that construction is generally supported by consortia of content providers or government entities that manage the initial and ongoing costs.

Specifically, there is concern that subsea cable securitization would result in increased regulation, malicious targeting and legal risk regarding data security.

As distributed acoustic sensing technology continues to develop, there is an opportunity for the United States and its allies to lead in engaging with industry and states to set standards regarding the use of subsea cables for sensing. Given that these nations already have a market advantage in subsea cables infrastructure development, they must ensure the technology is not misused, particularly given the intensification of strategic competition in the Indo-Pacific.

The subsea cable industry is an arena for international partnership, as opposed to competition. The announcement of a cofounded U.S., Australian and Japanese subsea cable connecting Micronesia is a clear example of the opportunities for collaboration with multiple beneficial outcomes.

The world relies on the interconnectivity that subsea cables provide to the global commons. It is unwise to let this vital infrastructure fall victim to the geopolitical tensions of the day.