Beneath the ocean waves, over 700,000 nautical miles of undersea cables link the far reaches of the world. These cable networks transmit government and private messages between continents in seconds, thereby forming the information backbone of modern society. The ubiquity of connectivity has rendered this cable infrastructure a largely invisible part of daily life, but instances of natural and human interference with cables has underscored their fragility. Due to their singular importance, cables have become attractive military targets. In February 2024, Houthi rebels severed three undersea cables in the Red Sea, disrupting 25 per cent of Europe and South Asia’s internet traffic, and visibly demonstrating the far-reaching effects of even small-scale cable attacks.

Since cables are so important for the national security of the United States and its allies, both Russia and China are actively developing the means to interfere with them. Yet there is nothing new about cable vulnerability. The United States cut undersea cables used by Spain in the Spanish-American War of 1898, while the British cut German cables in the lead up to both the First and Second World Wars. Even with the advent of radio and satellite communications, cables have remained a core element of international telecommunications because of their high capacity.

Improving the security of undersea cables has become a top priority for policymakers around the world, but they are often viewed in isolation from other telecommunications technologies. A key lesson from telecommunications history is that being able to seamlessly move message traffic between different communications networks is vital for information security. The emergence of large-scale space-based internet services, such as SpaceX’s Starlink, provide an alternative pathway for routing data if cables have been cut. New space systems cannot, however, fully mitigate widespread cable losses. Strengthening the resilience of existing cable networks requires having more cable routes, as well as investing in more ships that can rapidly repair undersea cables which have been severed. Concurrently, there needs to be plans in place to reallocate communications capacity between cables and satellites if one of them, or both, are degraded in a conflict or due to natural disasters.

The 19th and early 20th centuries witnessed profound changes in communications technologies that shaped the global balance of power. In August 1858, Queen Victoria and President James Buchanan exchanged messages using the first undersea cable that connected Britain with North America. By the early 20th century, undersea cables served as the nerve system of the British Empire, linking London with its faraway colonies and dominions.

The dual use nature of undersea cables immediately raised questions about their security. In 1884, countries from around the world gathered in Paris at a meeting of the International Telegraph Union, the precursor to the current International Telecommunications Union, to develop specific protections for undersea cables. Those present ratified an agreement to protect undersea cables in times of peace and established specific liabilities for a party that cut a cable, whether intentionally or not. Government representatives recognised that cables would be valuable targets in wartime. Like commercial communications satellites today, cables carried vital military and diplomatic messages that would be legitimate targets in a conflict. By the end of the century, cable cutting would become commonplace in wartime.

In the final decade of the 19th century, over 192,000 nautical miles of privately-owned cables and nearly 23,000 nautical miles of government-operated cables stretched under the ocean. At this point, two thirds of the world’s cables were British and one group, the Eastern and Associated Companies, owned approximately 45 per cent. Long before Elon Musk and Starlink, monopolies were commonplace in the global telecommunications market. Wireless telegraphy (radio) provided the only alternative means of communication, but the technology was still in a nascent form. Notably, the United States had not yet emerged as a global power and thus did not yet prioritise sovereign control over its strategic communications networks. Consequently, Britain was able to monopolise a significant portion of the global telecommunications network, ensuring the security of its information while being able to surveil messages transmitted by foreign powers.

During the Spanish-American War in 1898, the US Navy cut British and French cables as part of an information blockade. Soon thereafter, Captain George Squier, an officer serving in the US Army Signal Corps, described undersea cables as a ‘powerful instrument of war, more important than battleships and cruisers’. The United States, however, failed to challenge British hegemony in undersea cables. The UK possessed the preponderance of technical expertise for manufacturing cables and the specialised fleet of vessels for laying and repairing them. Washington would, however, invest in radio networks that could also send messages over long distances, but they were less secure than cables because radio transmissions could be easily intercepted or jammed.

In the 1920s a revolution in radio technology took place when shortwave radio hardware became widely available. This new technology bounced radio waves off the ionosphere, allowing messages to be sent over thousands of miles more inexpensively than cables. Quickly, businesses and individuals began sending more messages via radio than cable, threatening the viability of the global undersea information network. British officials concluded that cables needed to be maintained for security reasons, even if they were not financially competitive and therefore intervened to save their cable industry. This situation underscores that commercial and national security telecommunications requirements do not always neatly align. Combined, radio and undersea cables would provide redundancy for British telecommunications.

The dangers of foreign dependence on telecommunications would become especially apparent during the First and Second World Wars. In each conflict, the British successfully cut German cables, forcing Berlin to rely on radio, which could be intercepted, or to send messages via British cables, which UK intelligence officers were monitoring. The significance of the Anglo-American codebreaking effort during the Second World War is well known, but allied dominance in undersea cables also played a vital, albeit largely invisible role. These submarine information networks allowed the United States and Britain to securely share time-sensitive intelligence and rapidly coordinate military efforts in Europe, thereby contributing to the defeat of Nazi Germany.

By the end of the Second World War, the United States and Britain both possessed global telecommunications networks comprised of radio and undersea cables. The advent of the nuclear age made telecommunications security an even more urgent issue. Atomic weapons-testing demonstrated that a nuclear blast could render large portions of the ionosphere unusable for long periods of time, severely degrading radio communications. This problem had dire implications for transatlantic security. With the establishment of NATO in 1949, the United States needed reliable telecommunications links at all times with its allies in Europe. In this same period, the United States, Canada, Britain, Australia, and New Zealand were forming the Five Eyes intelligence alliance, which required the ability to rapidly and securely send intelligence information across the world. Undersea cables and radio formed the ‘connective tissue’ of these alliances, but they were increasingly vulnerable.

Five undersea cables between North America and Europe, complemented by radio circuits, provided the bulk of long-haul messages between the two locations. This included intelligence, warning information, and command and control messages for conventional and nuclear forces. In 1959 and 1960, Soviet trawlers cut these cables bringing communications to a standstill. Complicating matters further, radio across the Atlantic was unreliable due to ionospheric effects that made communications garbled. American, British, and Canadian intelligence officials were unable to determine if the Soviets had intentionally cut the cables, but the situation highlighted the weaknesses of their shared information networks. If the Kremlin cut the cables in the lead up to a superpower conflict, Washington might not be able to direct its military forces in Europe and co-ordinate with its NATO allies.

As an initial step towards bolstering the security of NATO’s information networks, American and Canadian naval vessels began patrolling the areas around the cables off the coast of Newfoundland and chasing away Soviet trawlers. American, Canadian, and British officials also co-operated in laying additional cables that could be used for both commercial and national security purposes as well as establishing new transatlantic radio circuits. These solutions only marginally reduced the vulnerability of US and allied command and control networks.

In these circumstances, the United States increasingly looked to emerging satellite technologies to be able to communicate with conventional and nuclear units across the globe. In the mid-1960s the United States began launching the first wave of commercial and military communications satellites. Within a decade, communications satellites transmitted just over one third of all US military long-haul communications and provided connectivity for NATO allies as well. The United States still heavily depended on undersea cables and radio networks. Problematically, international political upheavals in the 1970s would force the United States to vacate key radio communications facilities.

From the Second World War through the mid-1970s, a dusty US base called Kagnew Station in Asmara, Ethiopia was a critical node for all US military radio communications in Africa, the Middle East, and South Asia. A farm of large antennae connected policymakers in Washington with military commanders in those locations. Disaster struck in the early 1970s when Eritrean insurgents began targeting the American facility and at one point damaged communications equipment to the extent that all American military communications in the region were degraded. US officials considered moving the communications hardware to American sites in Iran, but those locations would be lost due to the 1979 Iranian revolution.

In theory, satellites relieved the United States of dependence on terrestrial telecommunications hardware, but a US communications satellite failed in orbit around the same time that Eritrean insurgents damaged the radio antennae at Kagnew Station. This convergence of political unrest in Ethiopia with a satellite malfunction over the Atlantic forced the United States to rely on radio sites in Europe and the Indian Ocean. These links were often unreliable due to ionospheric disturbances. Clearly, satellites did not fully mitigate terrestrial telecommunications dependencies.

As American anxieties about the vulnerability of command-and-control systems intensified in the 1980s, a telecommunications revolution was afoot. In 1988, AT&T finished TAT-8, the first fibre-optic transatlantic undersea cable. This new technology greatly expanded the capacity of undersea cables by transmitting messages in the form of light energy. In contrast with legacy cable technologies that could carry a maximum of only 4,000 telephone circuits, one fibre-optic cable carried over 40,000. These new cables would quickly spread across the world, enabling the information revolution of the late 20th and 21st centuries. Satellites and radio, however, remained vital, since cables could not satisfy mobile communications requirements.

A little more than three decades after the Cold War ended, threats to global telecommunications networks have only multiplied. Cyber vulnerabilities have taken centre stage in discussions about information assurance, which has overshadowed the insecurity of the physical infrastructure for transmitting information across the globe. This situation is especially urgent as US national security priorities have shifted to the Indo-Pacific, where American telecommunications networks are stretched across a vast ocean region that is disproportionately dependent on subsea communications.

At present, undersea cables, radio, and satellites are the three primary technologies that enable long-haul communications. Since the Soviet Union collapsed, all three of these have improved, but vulnerabilities have changed. Now, the global economy, and US national security organisations, are even more dependent on undersea cables for high-capacity communications. Satellites are vital for supporting mobile military forces and providing assured connectivity for nuclear forces. Threats to cables and satellites have only proliferated.

Just like during the Cold War and even earlier, commercial interests are inextricably linked with national security in the context of telecommunications. Today, the world depends on only four major companies for laying undersea cables: America’s SubCom, Japan’s NEC Corporation, France’s Alcatel Submarine Networks, and China’s HMN Tech, previously Huawei Marine Networks. The vast majority of cables are owned by private telecommunications firms. To prevent greater Chinese control over subsea information networks, the United States and its allies are trying to persuade countries not to use Chinese cables. Freezing China out of new cable projects makes it more difficult for Beijing to surveil both private and government messages, but these information networks are still vulnerable to physical interference.

In February 2023 two cables were cut connecting Taiwan with the Matsu Islands, leaving its 14,000 inhabitants without internet access. Reminiscent of the Soviet trawler incidents in the late 1950s and early 1960s, Taiwanese government officials suspect that a Chinese fishing vessel was responsible for the cuts, though it is not clear whether it was intentional. Cable cutting is a ‘gray zone’ activity, because it allows states to interfere with critical telecommunications infrastructure without rising to the level of general conflict. Just like in the cyber realm, attributing cable cutting and establishing whether it was intentional can be exceptionally difficult.

This 2023 Taiwan incident is only a small preview of the potential consequences of large-scale cable cutting in the lead up to a conflict involving the United States and China. Severing subsea cable networks in a crisis would not only disrupt vital government communications, but also lead to panic and social unrest if there is widespread loss of connectivity. To safeguard against this kind of situation, the United States and its allies must have adequate undersea cable maintenance and repair resources in place. There are only 60 cable-laying vessels in the world and they are already stretched to near breaking point due to constant demand for new cables as well as unrelenting maintenance requirements. SubCom has just six ships in its fleet. Cable-laying vessels can’t be built easily because they are highly specialised and therefore have a long lead time. Despite these challenges, more of these vessels are needed for a large-scale conflict in which cable cutting will be likely.

To deter cable cuts, the United States and other countries can increase the number and diversity of cable routes. Over a century ago, British officials constructed a cable network so large that over 40 cuts were needed to isolate London from the far reaches of empire. Achieving a high-level of telecommunications redundancy contributes to deterrence by denial. In this situation, an adversary will be less likely to expend limited resources in cutting cables if there is a low probability that it will have a significant effect. Recent reports suggest that the United States is expanding undersea cable routes to critical locations in the Indo-Pacific region, including Diego Garcia. Such a move makes it more difficult for China to impose an information blockage around key parts of the US military’s long logistical tail.

Pairing measures to enhance cable security with emerging space technologies offers another avenue for strengthening the security of telecommunications. Historically, communications satellites have been large, expensive, and deployed in higher orbits, where a satellite can ‘stare’ at approximately one third of the earth, providing connectivity to any users within its field of view. In the past decade or so, however, lower cost of launching satellites and miniaturisation of space systems has led to the creation of ‘proliferated’ satellite constellations that involve launching hundreds or thousands of satellites into lower orbits. SpaceX’s Starlink is one such example. These smaller satellites are cheaper and can therefore be easily replaced.

The war in Ukraine has demonstrated the value of proliferated satellite constellations during a crisis. Since Starlink communications terminals are small and relatively inexpensive, they have quickly become the information lifeblood of the Ukrainian armed forces. Russian forces have tried to jam Starlink communications, but have been generally ineffective. Countries that are heavily dependent on undersea cables should learn from Ukraine’s experiences and have plans in place to use proliferated satellite communications if cables are severed due to an attack or natural disaster. These satellites cannot completely fill a communications gap from widespread loss of cable, but they can at the very least ensure that vital messages get through.

Telecommunications networks constitute the ‘soft underbelly’ of the American war machine and are therefore key targets for its adversaries. The challenge is not solely military in nature. Severing undersea cables would have spillover effects, since they form the global information backbone. Consequently, strengthening their security is vital from a ‘whole of society’ perspective. Investing in more undersea cable routes and increasing the number of cable-laying vessels are both necessary for the United States to improve the resilience of its telecommunications infrastructure. Emerging satellite communications constellations cannot alone solve the cable security problem, but they are an important part of the solution. The United States should pursue a layering strategy in which communications capacity can be shifted between the space and subsea domains if these technologies are degraded due to natural disaster or attack. Rather than being discrete technologies, undersea cables and communications satellites are two components of one information space and their effective integration will better ensure the free flow of vital messages in times of crisis.