Modern Society Supported by Submarine Cables: Japan's Strategy and Outlook for Protecting Data Sea Lanes

Approximately 99% of international communications, including the internet, do not rely on artificial satellites in space, but rather on optical submarine cables laid on the ocean floor. Often called data sea lanes (maritime traffic routes positioned as strategically important from the perspectives of economy and security, and which should be secured in times of emergency), these optical submarine cables can transport large amounts of data at once without delay, serving as critical infrastructure for modern society where even the slightest lag is unacceptable, such as in financial transactions and online gaming.

Looking at Japan alone, hundreds of terabits per second of bandwidth are required to support domestic internet traffic (the volume of data communication flowing over a network and its congestion level), but satellite communications can only secure about 0.1% of that. To use an analogy, it is like 130 million people trying to share water from a single water pipe; satellite communication alone cannot handle it. While SpaceX's Starlink is leading in expanding satellite bandwidth, the reality is that this massive gap remains unfilled. In recent years, the spread of AI and cloud services has led to an explosive increase in the amount of data exchanged worldwide. To address this, massive investments are being made one after another in Australia and various parts of Asia to install new, higher-capacity, and faster cables.

Submarine cables have long been considered important as communication lines, and cutting an opponent's communications has been a standard tactic in military conflicts during global wars and regional disputes. During the Meiji era, the Japanese military once cut a submarine cable installed by Russia to blockade Port Arthur in China. Furthermore, when World War I broke out, the UK cut German submarine cables in the North Sea. Although the connection to military activity is unclear, an incident occurred in 2013 in Egypt where submarine cables were cut by unknown parties. Submarine cables are about 6 cm in diameter in coastal areas and about 2 cm in the open sea or deep-sea areas. Even with thicker outer casings, the reality is that there are no effective protective measures, as they can be easily cut by anchors or destroyed by underwater drones.

What would happen if submarine cables were cut right now? Services with servers overseas would become unusable, so YouTube would repeatedly buffer, and while Google search itself might work, none of the links would open. Credit card payments also rely on international authentication networks like Visa and Mastercard, so signs saying 'cash only' might suddenly appear all over town. While services where infrastructure is completed domestically, such as LINE, Yahoo! Japan, and domestic bank ATM networks, could be said to continue operating normally, some might stop working depending on the location of their data centers.

Currently, these submarine cables are more than just communication lines; they have become an area involving the balance of power and security between nations. For example, as tensions between the United States and China intensify, the U.S. is strengthening moves to exclude Chinese companies from its communication networks. In fact, there is a case where a cable project that was planned to pass through Hong Kong was suddenly canceled due to security concerns. In Japan, too, it is necessary to reduce the risk of data interception and the risk of cables being intentionally cut in areas like the South China Sea, where there are many troubles. Therefore, to secure safe communication routes without relying on specific countries, Japan is currently participating in new projects, such as one that directly connects Japan to the West via the Arctic Ocean, to diversify risks.

Looking at Japan, about 90% of the landing stations (critical facilities for connecting international and domestic submarine cables that have passed through the sea to terrestrial networks) that connect Japan to overseas, as well as the data centers that process data, are concentrated around Tokyo and Osaka, which is said to be a weakness. If a large-scale disaster such as a Tokyo inland earthquake or a Nankai Trough mega-earthquake were to occur and these facilities were damaged all at once, there is a risk that the internet across Japan would become dysfunctional. Therefore, the government is promoting a concept called the Digital Garden City Super Highway. The plan is to create a disaster-resilient network by installing submarine cables around the Japanese archipelago and dispersing hubs to Hokkaido, Kyushu, the Seto Inland Sea, and other areas. However, since enormous amounts of electricity are required to operate giant data centers for AI, how to develop electricity supply networks (power grids) and communication networks as a set is a major current challenge.

Furthermore, there is the problem of a shortage of specialized ships for installing cables on the ocean floor. Currently, three major companies capable of manufacturing submarine cables—one in the U.S., one in France, and NEC in Japan—account for more than 90% of the global market share. Because NEC can complete everything from parts manufacturing to assembly domestically, it is highly regarded worldwide for its safety, with low risks of information leakage or interference from other countries. However, with the global expansion of communication networks, there is a shortage of ships to lay the completed cables in the sea. If Japanese cables were cut due to a disaster or incident, relying on foreign ships for repairs could lead to significant delays in restoration. Therefore, the importance of securing ships within Japan that can be operated flexibly in emergencies is increasing.

Based on these various risks, the government is also stepping up its countermeasures. Previously, the safety management of communication facilities was basically left to private telecommunications companies, but this is shifting toward a strict, government-led system. With an eye toward 2026, the government plans to review related laws and rules and establish specific standards, such as strict management to prevent illegal entry into facilities and burying cables in sand in shallow waters to prevent them from being damaged by ship anchors or fishing nets. In addition, the government is strengthening its monitoring and protection system by specifically designating companies that own many cables connected to Japan and making it mandatory to notify the government in advance when introducing equipment that is important for security.

The top priority for submarine cable maintenance has completely shifted from reducing communication costs to ensuring a safe, reliable communication network that never goes down. As data traffic increases further due to the spread of AI, strategic infrastructure investment is essential for Japan to remain a hub for global data communication. Also, existing cables laid about 20 to 25 years ago are all reaching the end of their lifespan, and the cost of updating them alone is enormous. This massive project, which is easily affected by weather and requires large amounts of funds, has exceeded the limits of what can be maintained by the self-help efforts of a single company. Building a system where the government and private companies work together to protect Japan's data communication network, including seismic reinforcement of aging facilities and securing specialized ships, is an issue that must be addressed immediately.