To keep the world’s data flowing, countries need to quickly fix broken undersea cables
By Aaron Bateman | July 29, 2025
More than 550 submarine cables, stretching in excess of 1 million kilometers along the seabed, serve as the information highways for both civilian and defense organizations. Image: Cable data by Greg Mahlknecht, map by Openstreetmap contributors, CC BY-SA 2.0 , via Wikimedia CommonsShare
In the midst of US-Soviet tensions over Berlin in early 1959, five transatlantic submarine cables suddenly stopped working. Alarm bells rang in Washington since these undersea information networks carried NATO’s most sensitive intelligence and defense messages across the Atlantic. The United States and its allies initially suspected that the Kremlin might have purposefully cut the cables because a Soviet trawler was in the vicinity, but evidence was lacking. Nevertheless, because of this incident, NATO made cable resiliency a high priority.
Over the last couple of years, damage to submarine cables in the Baltic Sea, the Pacific Ocean, and the Red Sea have raised anxieties worldwide about the vulnerabilities of subsea information networks. These concerns are warranted; submarine cables are the physical infrastructure of global connectivity. More than 550 submarine cables, stretching in excess of 1 million kilometers along the seabed, serve as the information highways for both civilian and defense organizations. The same cables that connect billions of users to the internet also transmit sensitive defense-related messages. The fact that cables are lengthy, immobile, and land at fixed points complicates efforts to secure them against both intentional acts of interference and accidents.
The spate of cable breaks in the Baltic Sea in late 2024 immediately raised suspicions among European officials that sabotage was to blame. Since then, consensus has emerged that these incidents were likely accidental. Also in 2024, multiple cables in the Red Sea broke, disrupting internet traffic between Asia and Europe. These cases underscore the fragile nature of the submarine cable networks that carry more than 95 percent of global telecommunications.
During the Cold War—just like today—the United States and its allies had to contend both with accidental cable breaks on a regular basis and the threat of sabotage. Consequently, the United States invested in alternate means of communications, cooperated with allies to secure access to cable-repair vessels, and diversified cable routing. These elements that have stood the test of time should form the basis of US and allied cable resiliency strategies today. America’s primary objective should be to keeping data flowing.
To do this, the United States and allies must expand their repair infrastructure: The global cable-laying and repair fleet, composed of 62 vessels, is aging and not keeping pace with submarine cable growth. By 2040, industry analysts anticipate a 48 percent net increase in total cable kilometers. In this same period, nearly 50 percent of cable-laying and repair ships will reach the end of their lives. More investment in these highly specialized vessels is needed sooner rather than later. Cable maintenance infrastructure is inextricably linked with US national security interests globally, but especially in the Indo-Pacific. Indeed, Japan, South Korea, Australia, Taiwan, and New Zealand, all rely on subsea cables for connectivity with the United States.
A fragile infrastructure. Since the dawn of the transoceanic cable age in 1866, wayward anchors and fishing nets have been far greater threats to cable networks than saboteurs. A 1911 report by the British Committee of Imperial Defence observed that fishing trawlers frequently severed cables. From 1957 to 1959, there were more than 122 reported transatlantic submarine cable breaks. Over the last 15 years, there have been approximately 200 cable faults a year across the world.
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During the Cold War, Soviet fishing boats caused multiple cable breaks. In the wake of those incidents, UK technical experts considered developing new technologies to detect active interference with cables. In the end, American and British officials recognized that detecting interference was not the main solution to the cable vulnerability problem. Especially in wartime, defense planners wanted to ensure that messages continued to flow when cables were severed and there would be little time to determine if cable cutting was intentional. Restoring connectivity as quickly as possible was paramount.
Consequently, American and allied officials placed great emphasis on bolstering resilience by having multiple, redundant information pathways in case cables ceased to function. AT&T and the British Post Office laid new transatlantic cables farther from highly trafficked fishing grounds. They also expanded the number of transatlantic cables. In 1960, another transatlantic cable broke. But vital message traffic was rapidly shifted to a newly laid cable until the damaged cable could be repaired, underscoring the value of routing diversity. In the Pacific, the United States and the British Commonwealth joined their cable networks, permitting message traffic to be rerouted when breaks occurred.
In addition to expanding the number of cables, US officials developed a “layering strategy,” premised on using cables and radio in tandem to strengthen the resilience of their information networks. In the mid to late 1960s, the maturation of satellite communications, alongside radio and cable, completed the US connectivity triad. Cable cutting remained a threat, but the US layering strategy made it much more difficult for the Kremlin to use cable attacks to comprehensively degrade NATO’s connectivity.
The value of layering was validated when a cable connecting the US nuclear early warning radar in Greenland with North America was severed multiple times in the early 1960s. This same cable provided connectivity with an Air Force satellite tracking station in Greenland, underscoring the linkages between the space and subsea environments. While repairs were completed, the Pentagon used radio circuits between Greenland and the United States as a backup, keeping essential nuclear and satellite data flowing.
Subsea cables continue to enable space operations. Svalbard, a Norwegian archipelago in the Arctic Ocean, is home to one of the largest satellite ground stations in the world. Two cables deep beneath the frigid Arctic waters carry data between the Svalbard station and the Norwegian mainland. As tensions mounted in the lead up to Russia’s invasion of Ukraine in 2022, one of the cables was severed. Some Norwegian officials initially suspected sabotage, but further investigation has been unable to prove deliberate interference. Even though the impact on connectivity was minimal, it reminded government and commercial actors of the potential widespread effects of cable breakdowns.
Natural disasters have also repeatedly underscored the need for contingency plans. In 1964, an underwater earthquake severed a segment of the Commonwealth Pacific Cable that stretched between Canada and Hawaii, cutting off defense and commercial message traffic. Fortunately, shortwave radio provided a backup. Similarly, in 2022 an underwater volcano destroyed Tonga’s one and only submarine cable. Shortly after, SpaceX donated 50 Starlink terminals to reestablish the island’s internet connectivity. Two years later, the cable broke again. Restoration took more than a month.
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Applying the lessons of history. The United States and its allies should take heed of the lessons of history and prioritize resiliency through further diversifying cable routes, increasing investment in repair infrastructure, and bolstering their ability to shift the vital message traffic to satellite communications in a crisis. But it is necessary to stress that large-scale constellations of communications satellites, like Starlink, have significant capacity limitations compared to cables. Satellite communications are therefore an inadequate substitute for all but the most important cable traffic.
Even though US and allied national security organizations depend on subsea networks, their laying and repair is largely driven by market forces. Since cables are expensive, consortiums of telecommunications and tech companies like Meta and Google oftentimes finance them. Similarly, repair vessels are primarily owned by commercial firms. In the Cold War, the British government maintained a small fleet of repair vessels, but the privatization of the overseas telecommunications element of the British Post Office, as well as Cable and Wireless Limited, placed these ships in private sector hands. The combination of high price tags for cable ships—oftentimes $100 million or more per vessel—and narrow profit margins in the repair market leaves cable firms with few incentives to build new ones.
In response to cable security concerns, the United States has created a Cable Security Fleet program that consists of two commercial vessels contracted by the US government to provide cable repair services in a national emergency. But more action is needed. To this end, American policymakers should consider subsidies for cable-laying and repair companies that will incentivize the construction of new ships.
Partnering with allies is another necessary measure. In the Cold War, the US government contracted British ships to repair cables that carried command and control data. Today, more coordination is needed with allies and partners to secure dedicated access to repair services for essential cables in times of crisis.
A strategy that prioritizes mitigating cable damage through rapid repair does not exclude greater investment in technologies for surveilling undersea infrastructure. Large networks of underwater autonomous vehicles with sensors for monitoring the seabed environment can be of great assistance in detecting threats to submarine cables. Better sensing can also enhance attribution efforts in response to interference, but such attribution will have important limits. Enhanced monitoring does not necessarily make it easier to determine in a timely manner if ships are purposefully dragging their anchors and trawls across submarine cables. Moreover, detecting interference does not ensure the resilience of the network.
Moving forward, the resiliency of subsea cables is going to become an even more urgent issue as demand for connectivity surges. Indeed, cables constitute the “connective tissue” of the digital revolution that is reshaping the global economy and modern warfare. Subsea cables enable artificial intelligence innovation as well as the Department of Defense’s new global command and control initiative. These are but two examples illustrating that submarine cables are vital components of US efforts to remain the leading technological power. But growth in cable networks cannot be sustained without far more investment in the repair infrastructure that keeps them functional in times of peace and war.
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