Japan needs to protect its undersea lifelines

With the launch of Prime Minister Sanae Takaichi’s second reshuffled Cabinet, her administration should make protecting Japan’s undersea cables a priority.

These cables are critical infrastructure not only for Japan but for the countries with which it communicates and does business. Given the scale of the challenge, protecting them will require a “whole-of-government” approach.

This might be more difficult than it sounds. Because the issue of submarine cables is divided between multiple agencies and a handful of ministers, it may even require the temporary creation of a “special minister for undersea cables” who can devote his or her full attention to the matter.

Japan’s security depends not only on the ships that patrol its waters, the aircraft that guard its skies and the soldiers manning observation posts along the country’s thousands of miles of coastline, but also on a largely invisible network resting on the ocean floor.

Submarine fiber-optic cables carry approximately 99% of Japan’s international data traffic. Financial transactions, government communications, cloud computing, military coordination, industrial supply chains, news reporting and ordinary telephone and internet services all depend upon them. These cables are therefore not merely telecommunications infrastructure; they are strategic lifelines — and potentially one of Japan’s greatest vulnerabilities.

The country’s dependence on submarine cables arises partly from geography. As an island nation, it lacks the extensive cross-border terrestrial fiber networks available to continental countries. Satellites provide essential backup and specialized services, but they presently cannot replace the capacity, speed and cost-effectiveness of modern fiber-optic cables.

Japan is an important node in the global cable system, with at least 20 international cable landing stations connecting it with North America, Southeast Asia, Australia, Taiwan, South Korea and other destinations.

One vulnerability is geographic concentration. Many international cables land in relatively limited areas, particularly around the Boso Peninsula in Chiba Prefecture and the Shima Peninsula in Mie Prefecture. Strategically, however, it creates potential points of failure. A major earthquake, tsunami, coordinated act of sabotage or an attack on landing facilities could disrupt several systems simultaneously.

Japan’s seismic environment adds to this danger. The 2011 Great East Japan Earthquake demonstrated that modern communications networks contain considerable redundancy, but it also showed how natural disasters can strike electricity supplies, coastal facilities and terrestrial connections at the same time. An anticipated Nankai Trough earthquake could similarly affect cable routes and landing stations along the nation’s Pacific coast.

More common threats come from fishing equipment and ship anchors. Worldwide, submarine cables suffer roughly 150 to 200 faults annually, with more than 80% caused by human maritime activity, principally fishing and dragged anchors, according to the International Telecommunication Union.

Nevertheless, the same actions can be used deliberately while allowing the perpetrator — China and Russia in particular — to claim it as an accident.

Recent incidents around the Baltic Sea and Taiwan demonstrate this problem. In January 2025, four international cables near northern Taiwan were damaged, while another cable incident the following month led Taiwanese authorities to prosecute the captain of a Chinese-owned vessel. Investigations into such cases must distinguish carelessness from hostile intent. Yet repeated damage involving vessels with opaque ownership, unusual movements or links to potentially hostile states cannot simply be dismissed.

In a crisis involving Taiwan or the East China Sea, Japan’s submarine cables will undoubtedly become targets. An adversary might not need to disconnect the nation completely. Cutting several carefully selected routes, damaging landing facilities, attacking network-management systems or creating uncertainty about the reliability of communications could be sufficient to slow financial markets, disrupt logistics, complicate Self-Defense Forces operations and weaken public confidence.

Cable security also involves more than physical cutting. Landing stations and network-management systems face cyberattacks, espionage and supply-chain compromise. Ownership and maintenance arrangements frequently cross national jurisdictions, further complicating responsibility.

Repair capacity represents another concern. Cable repair requires specialized ships, trained crews, replacement cable and permits from the states whose waters may need to be entered. Following a major regional disaster — or deliberate attacks against several systems simultaneously — Japan could face delays while competing for limited repair capacity.

The nation consequently needs a comprehensive cable-security strategy. First, it should accelerate the geographic diversification of cable routes and landing stations. New connections should be distributed beyond the traditional Boso and Shima clusters, with greater use of Kyushu, Hokkaido, the Sea of Japan coast and strategically appropriate islands. Terrestrial backhaul routes from landing stations must likewise be diversified; moving the landing point accomplishes little if communications converge again through one vulnerable corridor.

Second, the government should support sufficient Japanese-controlled cable-laying and repair capacity, including trained crews, domestically produced components and protected stocks of replacement equipment. Cable repair should be incorporated into national emergency exercises alongside disaster response, cyberdefense and continuity planning.

Third, Japan must improve maritime monitoring around critical routes and landing points. The Japan Coast Guard, Maritime Self-Defense Force, police, telecommunications companies and intelligence agencies require mechanisms for rapidly sharing vessel-tracking data, cable fault information and indicators of suspicious behavior.

Fourth, institutional responsibility must be clarified. The Ministry of Internal Affairs and Communications regulates telecommunications, while the Coast Guard has primary responsibility for maritime law enforcement and the Self-Defense Forces possess important surveillance and emergency-response capabilities. Japan should establish clear procedures for determining when an ordinary cable accident becomes a national security incident and which authority then takes the lead.

Finally, Japan should deepen cooperation with the United States, Australia, Taiwan, European partners and Pacific island countries. This should include intelligence sharing, coordinated repair arrangements, joint exercises, trusted supply chains and assistance in developing secure regional cable networks. Satellite communications, including low-Earth-orbit systems, should provide emergency redundancy, although they should be understood as supplements rather than substitutes for fiber-optic cables.

Japan once treated economic efficiency as the principal measure of infrastructure policy. The present security environment requires a different standard: resilience. Redundant routes, reserve capacity and specialized repair ships may appear expensive during normal times. Following a natural disaster or deliberate attack, however, they would be priceless. Protecting Japan’s undersea cables is ultimately about ensuring that the nation can continue to communicate, govern, trade and defend itself under the most difficult conditions. The cables may be nearly invisible, but they must no longer remain strategically overlooked.

Robert D. Eldridge, a former associate professor at Osaka University, served as the political adviser to the U.S. Marine Corps in Japan and Hawaii and was a Ministry of Foreign Affairs, Republic of China (Taiwan) Fellow at Tamkang University in 2024.