To Secure Undersea Cables, Take Lessons from the British Empire’s All-Red Line

In the late 19th century, Alfred Thayer Mahan’s The Influence of Sea Power upon History: 1660–1783 made a case for the importance of naval power, including a strong merchant marine to shape world events and enable free trade. His arguments have stood the test of time, in part because he also considered the role of technology. For example, he wrote that the then-new technology of submarine telegraph cables altered strategy, at least with respect to blockade.¹ As Brent Sadler notes in his insightful book U.S. Naval Power in the 21st Century, Mahan’s work is especially relevant to modern supply chains, distributed manufacturing, and instantaneous global communications via undersea cables.²

Fiber-optic submarine cables, like the previous centuries’ merchant ships plying sea lines of communication, are direct international communication links. Through them, a vast amount of video, voice traffic, and data flows around the globe 24/7. Financial services, news organizations, distributed manufacturing, and international command and control require these cables to function well. There are currently more than 500 garden-hose-diameter international cables touching 1,636 cable landing stations (current or planned)—the arteries of modern media, social, diplomatic, commercial, and military communications.³

These undersea cables route streams of data to data centers on land, mainly operated by large technology platform companies such as Microsoft (Azure), Google (GCP), Amazon (AWS), Meta (Facebook), and Tencent (China). The “cloud” is indeed beneath the sea.⁴

In 2022, Google, Amazon, Meta, and Microsoft used 71 percent of all used international internet capacity.⁵ Each operates its own data centers to process and store content. To deliver that content, they must ensure their data centers are well connected to each other and to other networks and interconnection locations. The demand for international bandwidth (roughly doubling every two years) drives the development of data centers and undersea cable systems.⁶ This global infrastructure consists of several layers: cloud regions and data centers, the network of cables connecting them, and the ports where cable repair ships are based (“base ports”). In many ways, these elements mimic maps from previous centuries showing trade through ports and shipping lanes. (An interactive map showing these modern global infrastructure layers is available at a Google Maps site.)⁷

Cable Repair in Peace and War

Base ports contain marine depots where cable spares needed for repair are stored ready for use. By contract, cable repair ships with their highly trained and seasoned crews are typically required to sail within 24 hours of notice of a fault to a cable system. In 2023, cable systems worldwide suffered 206 faults, the majority caused by fishing and anchoring.⁸ While submarine cables can be cut, they can also be repaired—if the cable ships can reach the fault.

In peacetime, repairing cables is normally feasible and done with impressive efficiency. In wartime, however, accessing cable faults is a major challenge. State practice and international law have consistently held that submarine cables, cable repair ships, and cable landing stations are legitimate military targets.⁹ This status was confirmed in 2023 in the Newport Manual on the Law of Naval Warfare:

Military communications cables are military objects and may be targeted during armed conflict. Most military communications cable traffic, however, travels through commercial submarine cables. Military data through such cables is indistinguishable from ordinary commercial Internet traffic. The specific pathways that data packets travel through commercial submarine cables cannot be predicted or controlled by the cable owners. Although civilian submarine cables are civilian objects, their common use by the armed forces means that they may make an effective contribution to military action and their disruption or destruction may offer a definite military advantage.¹⁰

Indeed, there is a long history of submarine communications infrastructure being targeted during armed hostilities: from Chile in 1872 cutting the subsea telegraph cable between Lima, Peru, and San Francisco, California, during a war between Chile and Peru and Bolivia; to Saudi Arabia’s bombing in 2022 of the telecommunications facility at Al-Hudaydah during its war with Houthi rebels in Yemen, which destroyed the landing station for the FLAG Alcatel-Lucent Optical Network and SeaMeWe-5 undersea fiber-optic cable systems.¹¹

Naval strategists such as retired Captain Brent Sadler and retired Admiral James Stavridis understand the strategic importance of submarine cables but wrestle with defining an optimal strategy that would allow using cables in wartime while denying their use to an enemy.¹² Despite the modern emergence of fiber-optic cables and data centers, this strategic challenge remains. The All-Red Line, the strategic submarine telegraph system that bound the British Empire together, offers important lessons.

Undersea Cables of the All-Red Line

In 1866, the successful operation of a transoceanic submarine telegraph network changed international communications. With amazing rapidity, submarine telegraph cables were laid across the world’s oceans, reducing communication lags from days and weeks to minutes. The British government quickly grasped the strategic value of submarine telegraph networks to control and administer the British Empire, as the Imperial Defence Committee noted in a secret 1910 memo: “The maintenance of submarine cable communications throughout the world in time of war is of the highest strategic and commercial interests of every portion of the British Empire.”¹³ A decision was made at that time to connect all the colonies and possessions with submarine telegraphs. For security, it was further decided that all landing points needed to be on British territory and all cable landing stations staffed by British telegraphers. Since maps of the time frequently showed the British Empire in red, the system became known as the “All-Red Line,” as depicted in a 1902–3 sketch (Figure 1).¹⁴

The Eastern Telegraph Company, a private company, laid much of the All-Red Line (just as private companies mainly lay today’s internet undersea cable systems). The company received government subsidies to build some of the lines and cable stations needed for relays on remote islands (the Cocos Islands, Fanning Island, and Norfolk Island). The All-Red Line was made resilient and robust by numerous cross-connecting cable systems and, in some cases, terrestrial telegraphs. This system served the British Empire with reliable and secure global communications.

British strategists on the Imperial Defence Committee, however, understood the system would be vulnerable in a military conflict. In 1911, they estimated it would take 49 cable cuts to isolate Great Britain and between 5 and 11 cuts each to isolate its major colonies.¹⁵

To protect strategic communications, the British took some comfort in the fact that the submarine cable routes in most cases were in the vicinity of major commercial shipping routes patrolled by the Royal Navy. In addition to owning more than 60 percent of the world’s submarine cables, by 1904 the British had a fleet of 28 cable ships flying the red ensign and available in wartime. Near some cable landing stations, guns were deployed to deter raids, and cable stations secretly stored reserve instruments and spare cable. Decoy cables also were laid from the cable landing station, extending a few miles offshore and designed to confuse raiders who sought to cut the cable in shallow waters.¹⁶ Thus, on the eve of World War I, it was noted in the British press that:

The strength of our position is due to the past policy of fostering a system of British-owned cables, spread like a net all over the world, and constituting a monopoly which has grown stronger and stronger with each succeeding year. . . . Now that it has been multiplied many times over . . . the telegraph may be expected to confer its greatest benefits from the strategical point of view.¹⁷

This forecast proved accurate. While Germany did cut cables and attack cable stations at the Cocos and Fanning Islands, communications were never lost between various parts of the British Empire. Germany, on the other hand, had all its cables cut in 1914 and was isolated for the duration of the war. As a result of the Royal Navy’s sea control, German cruisers were eliminated as a threat and German cable ships could not carry out repairs. In contrast, British cable ships maintained the British cables and laid new cables throughout the war. Even by today’s standard definition of internet network resilience, published by the U.S. National Institute for Standards and Testing, the All-Red Line remained remarkably resilient in that it could: (1) operate in a degraded mode if damaged, (2) rapidly recover if failure occurred, and (3) scale to meet rapid or unpredictable demands.¹⁸

Lessons from the All-Red Line

From the experience of the All-Red Line, coupled with Mahan’s core strategic sea power views, there are lessons to inform contemporary naval strategists with respect to fiber-optic cables. Just as Mahan considered the new technology of the submarine telegraph, today’s strategists must consider modern technology such as cloud computing.

Mahan did not place responsibility for sea power solely on the Navy. In his time, merchant ships and privately held infrastructure, such as coaling stations, were also key elements. Today, private firms are the primary builders, owners, and operators of submarine cable systems. Sadler defines naval statecraft as the synthesis of strategic objectives with national power to form a course of action by “optimizing [government and private sector] organizational structure for great power competition.”¹⁹ This is particularly important for a U.S. submarine cable strategy, considering more than 14 government agencies own a piece of the cable puzzle, and no single agency is in charge.

In addition to military-private industry cooperation, there is also precedent for the armed forces and diplomatic corps to work together in wartime to shut down communication infrastructure (cable and radio facilities). At the start of World War I, Britain pressured neutral countries “with German-owned and -operated cable and radio stations in their territories to shut these facilities down.”²⁰ Today, the U.S. Trade and Development Agency is employing a similar tactic in offering grants valued at millions of dollars to companies in countries in which the planned SeaMeWe-6 cable system is to land, provided those countries reject a Chinese supplier for the system.²¹ Thus, naval statecraft must incorporate interagency coordination and private industry to be effective on a global scale.

Just as in the days of the All-Red Line, strategic use of submarine cables in wartime requires multiple cable landings with geographically diverse cable systems operated by proven or likely allies. Fortunately, the commercial cable industry has done an incredible job of laying cables in diverse paths across the world with the latest technology with little or no government funding. The major technology companies have deployed their capital to lay new cable systems with the latest fiber-optic technology connecting their data centers. Internet resilience relies in part on these cable system owners agreeing to act as backup for other cables if they are damaged until they can be repaired.

As the Imperial Defence Committee did in the early 20th century, today’s strategists should analyze the current cable infrastructure and landing stations to determine how many cable cuts would be required to isolate the United States. The key systems would be those that connect the United States and its likely key allies and U.S. bases in a great power conflict. At a minimum, this would include the United States (including Puerto Rico, the U.S. Virgin Islands, and Guam), the United Kingdom (including Gibraltar and Diego Garcia), France, Denmark, Norway, Italy, Japan, Korea, Australia (including the Cocos Islands), New Zealand, Singapore, the Philippines, Taiwan, and India.

The All-Red Line did what it could for its time to monitor its cables and cable landing stations. The United States must rethink monitoring submarine cables for hostile interference and take advantage of modern technology. Warships will be too few and overtasked to patrol these key cable systems. Drones, aerostats, and maritime patrol aircraft could contribute to maritime domain awareness, complementing industry monitoring practices using AIS, coastal radar, and aerial and surface surveillance. New techniques using AI to analyze cable operational data for anomalies indicating activities near cables show promise. These advancements mean, for example, that it would be commercially viable to provide a degree of cable protection up to 100 nautical miles from shore at distances up to nine nautical miles from a cable without human involvement.²²

A fundamental strength of the All-Red Line was the availability of the largest fleet of cable repair ships in the world (28 at its peak in 1904). Today, there are only two U.S.-flagged subsea cable repair ships in operation. These ships and their U.S. Merchant Marine crews were part of the 2021 Cable Security Fleet Act, which Congress funded in March 2024 by the Consolidated Appropriations Act at an annual cost of $5 million per vessel. However, the original legislation called for six cable ships. The 2021 law should be amended to fund six cable ships (with annual cost increases) as the minimum fleet size needed to provide worldwide coverage. For $30 million, this program would be a national security bargain.

Strategic coordination between the U.S. cable repair fleet and cable ships of the UK, France, and Japan—alongside SubCom, an American company—would greatly enhance repair capabilities. However, the United States needs its own reliable U.S.-flagged and -crewed ships for immediate access in wartime, whether acting with allies or independently.

These U.S. naval statecraft measures would strengthen the access to and resilience of submarine cables and the data centers to which they connect. The United States, however, will fare no better than Germany in World War I if the Navy fails to exercise sea power to control the oceans. If a U.S. or allied cable is cut or damaged in wartime, sea power enables cable ships to repair it while denying the same ability to enemies. On this point, Mahan’s view of sea power and its critical importance to the United States remains squarely on target. Unfortunately, the Navy lacks the numbers of ships and a naval statecraft strategy to meet this target in the face of ongoing great power threats.