The underlying risk of Japan's undersea cables

Japan Times

16-06-2025

Recent reports of suspected sabotage targeting undersea cables near Taiwan and in the Baltic Sea are highlighting a vulnerability in Japan — an island nation that relies almost entirely on such cables to stay connected to the rest of the world.
The government is increasingly aware of the risk. Tucked into this year's economic and fiscal policy guidelines, referred to as honebuto no hōshin, which set the tone for budget planning for the next fiscal year, is official recognition of submarine cables as strategic infrastructure vital to Japan's economic security.
What exactly are undersea cables, and how real is the threat of disruption — especially for a country such as Japan, which faces frequent natural disasters and growing geopolitical tension?
What are undersea cables and how connected is Japan?
Roughly the thickness of a garden hose, undersea cables contain strands of optical fiber that allow for massive data transmission at lightning speed with high security.
These fiber-optic lines handle 99% of Japan's international communications, powering everything from email and banking to video calls and cloud computing. They're the invisible infrastructure that keeps the global internet humming.
There are some 600 subsea cables worldwide totaling over 1.48 million kilometers, according to TeleGeography, a U.S.-based telecommunications data provider.
Japan — a hub of undersea cables connecting the United States and Asia — is directly connected to 20 to 30 international cables, according to the Internal Affairs and Communications Ministry.
Would Japan's international communications be cut off if undersea cables are damaged or sabotaged?
The short answer is no. Cutting one or two submarine cables won't send Japan — or any major country — offline. Global networks are designed with redundancy in mind, allowing traffic to be rerouted almost instantly via alternative paths.
In fact, cable damage is actually quite common, but it's rarely dramatic.
Most incidents are caused by aging infrastructure — cables typically last 25 to 30 years — or human activities such as fishing and anchoring. According to the internal affairs ministry, Japan recorded two cable ruptures due to natural causes in 2023, four the year before, and six in 2021.
'If you tried to make them completely indestructible, like by cementing them in concrete, you wouldn't be able to repair them,' said a senior internal affairs ministry official in charge of undersea cable policies, who requested anonymity in line with ministry practice. 'Everyone knows that the cables can snap. The point is to be prepared when that happens.'
Could undersea cables be subjected to military attacks?
Suspected sabotage cases have made headlines but they remain the exception, not the norm.
The Baltic Sea incident in late 2024 drew international attention when a ship dragged its anchors along the seafloor for kilometers, severing cables along the way. The event led NATO to deploy military ships to patrol the area.
Taiwan has also faced repeated undersea cable cuts involving China in recent years. But Jun Murai, a professor emeritus at Keio University and expert in undersea cables, noted that these incidents are likely caused by Chinese fishing vessels rather than military activity.
'It's difficult (to say)' he said. "Fishing boats often appear (in Taiwanese waters) because China claims the South China Sea as its territory. And when the boats pass by, the cables get cut.'
The media reaction has nevertheless been intense, with accusations of deliberate sabotage. Murai, however, said that even countries in conflict often dispatch repair ships to fix damaged cables regardless of political tensions, as part of a long-standing industry norm.
'There may be security-related conflicts, but treating submarine cables themselves as weapons or military targets doesn't really benefit anyone,' he said. 'There are so many paths and providers that it's virtually impossible for everything to go down at once.'
The real vulnerability arises when a small island relies on a single cable. If that gets severed, the island can go completely offline, and repairs may take time — as reportedly happened when Tonga lost communications after an earthquake damaged its cable in June 2024.
What are the potential risks and challenges for Japan?
Japan's greatest vulnerability lies not in sabotage, but in its geography. As one of the world's most seismically active countries, it faces an ever-present risk of natural disasters damaging the cables laid deep underwater.
The 2011 Great East Japan Earthquake severely damaged several undersea cables connecting Japan and the U.S. across the Pacific.
However, thanks to preexisting redundancy measures, most users never experienced any disruption. Private companies had already secured alternative routes, and when cables were cut, they were able to borrow bandwidth or reroute traffic through other lines, preventing major outages.
More recently, the Noto Peninsula earthquake underscored the importance of backup infrastructure. While some submarine cables were affected, the more immediate issue was on land, where collapsed cellphone base stations left large areas without mobile service. In such emergencies, alternative technologies such as satellites or high-altitude platform stations could serve as communication lifelines.
'I think there are limits to capacity, so it may be difficult for these to serve as a true substitute for submarine cables,' the internal affairs ministry official said.
'But if communication can still be established via satellite, then people would still be able to contact someone or send an SOS. In that sense, securing alternative means of communication is extremely important.'
What is Japan's role on a global scale?
Japan plays a key role in the global submarine cable industry — not just as a hub for data traffic, but as one of the few countries with a domestic cable manufacturer.
Keio University's Murai noted that Japan is in a relatively strong position internationally, in part because so few companies in the world actually make these cables.
There are currently three dominant players in the global market: France's Alcatel Submarine Networks (ASN), in which the French government has a majority stake, U.S.-based SubCom, and Japan's NEC. Chinese firm Huawei has also been increasing its global market share in recent years.
Murai said that while political concerns have led some to hesitate over government-owned manufacturers such as ASN, NEC's status as a private Japanese company has helped grow its business, particularly as buyers seek stable, politically neutral sources for their infrastructure.
'So now ... NEC has become stronger,' he said.
Another challenge is Japan's limited number of cable-laying ships. KDDI and NTT both own such vessels, but NEC is the only cable manufacturer that does not own any, although it started renting one in 2022.
What's the government's role in preserving the cables?
The economic ministry has labeled these cables 'extremely important assets' in recent revisions to national economic security policy, underlining just how vital they've become in the digital age.
But what active steps are authorities taking to ensure that the critical infrastructure is protected?
The internal affairs ministry official revealed that a budget of ¥10 billion ($69.6 million) was secured in the fiscal 2023 supplementary budget to support the diversification of submarine cable routes and landing stations in Japan, with specific projects to be selected later this month.
'We are creating and advancing cable projects in response to private sector demands, as international communications are extremely important for Japan, which is surrounded by the sea,' he said.
While most submarine cables are built and operated by private companies, governments play a key role in securing global communications as businesses typically prioritize profitability.
For example, that can mean concentrating infrastructure in metropolitan areas such as Tokyo and Osaka in response to public demand.
Currently, most landing stations are clustered in the Kanto region's Boso and Shima peninsulas. Murai acknowledged this concentration poses a potential risk and said future infrastructure should be more evenly distributed to regions such as Okinawa, Hokkaido and Kyushu.
'Submarine cables used to be considered just communications infrastructure,' Murai said.
'But today, they're the foundation of the entire economy. Everything from artificial intelligence to health care, energy, and education depends on stable, high-capacity digital connections.'