What Would Happen If All Underwater Internet Cables Were Cut?

If all underwater internet cables were simultaneously severed, approximately 99% of international internet traffic would cease, causing a complete breakdown of global communications, financial systems, and digital commerce within hours. The world would effectively be digitally partitioned into isolated continents with no ability to communicate electronically across oceans.

The Hidden Foundation of Global Communications

The modern internet relies on an invisible network of submarine cables that most people never think about. These fiber-optic cables, stretching across ocean floors like a vast underwater web, carry virtually all international data traffic. Every email sent between continents, every video call across oceans, and every financial transaction between countries travels through these physical cables lying thousands of meters below the surface.

Currently, approximately 400 submarine cables span 1.3 million kilometers of ocean floor, carrying an estimated $10 trillion in financial transactions daily. Despite their critical importance, these cables are surprisingly fragile—in deep ocean areas, most are only about the diameter of a garden hose, yet they bear the responsibility of connecting billions of people worldwide.

The Immediate Consequences of a Global Cable Failure

If all submarine cables were simultaneously cut, the effects would be catastrophic and immediate. International banking systems would collapse as financial institutions lost the ability to process cross-border transactions. Global supply chains would grind to a halt as companies couldn’t communicate with overseas suppliers or track international shipments.

Stock markets would face unprecedented chaos, unable to coordinate with foreign exchanges or process international trades. The London Stock Exchange couldn’t communicate with New York, Tokyo would be isolated from European markets, and global financial coordination would become impossible.

Communications would revert to pre-internet methods, with international phone calls becoming impossible through traditional networks. Businesses with international operations would lose contact with overseas offices, effectively paralyzing multinational corporations.

Geographic Vulnerabilities and Chokepoints

The submarine cable network has critical vulnerability points that make a widespread failure more plausible than many realize. Nearly 97% of internet traffic between Europe and North America passes through just two geographic chokepoints: the region south of Greenland and the English Channel area. Both locations sit near known geological fault structures, making them susceptible to seismic events.

The United States faces particular risk due to cable concentration at specific landing points. The entire East Coast’s international connectivity funnels through just a handful of beach locations, including Manasquan, New Jersey, and Shirley, New York. If these landing points were compromised, hundreds of millions of Americans would lose international internet connectivity.

Historical Precedents and Natural Disasters

Complete cable failures have occurred before, though on smaller scales. In 1929, an underwater earthquake off Newfoundland triggered a massive submarine landslide that severed 12 separate transatlantic telegraph cables in sequence. The event introduced scientists to turbidity currents—underwater avalanches that can travel at 100 kilometers per hour along the ocean floor with enough force to snap steel cables.

More recently, a 2006 earthquake near Taiwan triggered turbidity currents that cut nine submarine cables over 26 hours, severely disrupting internet and phone service across Southeast Asia for weeks. Some repairs took over a month because there are fewer than 60 specialized cable repair ships worldwide—far too few to handle multiple simultaneous failures.

Geopolitical Threats and Intentional Sabotage

Beyond natural disasters, submarine cables face intentional threats. Western intelligence agencies have documented Russian submarines conducting surveillance operations near critical cable routes in the North Atlantic at levels not seen since the Cold War. Military strategists consider cable cutting one of the most powerful invisible weapons in geopolitics, capable of blinding an adversary without firing a shot.

The vulnerability is compounded by the fact that exact cable coordinates are publicly available on maritime charts—necessary for ships to avoid them, but also providing a roadmap for potential saboteurs.

Recovery and Repair Challenges

Repairing severed submarine cables is an extraordinarily complex process. Cable repair ships must locate the break using underwater vehicles, retrieve both ends of the cable from depths sometimes exceeding 8,000 meters, splice in a new section, and carefully lay it back on the seafloor. The process can take weeks for a single cable.

With only 60 repair ships globally, a coordinated attack or major geological event affecting multiple cables simultaneously could create repair backlogs lasting months. During this time, internet traffic would attempt to reroute through remaining connections, likely overwhelming surviving cables and causing widespread slowdowns or failures in the remaining network.

Alternative Solutions and Future Preparations

Recognizing these vulnerabilities, tech giants like Google, Meta, and Microsoft have invested billions in private submarine cable networks to reduce their dependence on shared infrastructure. However, these efforts primarily protect corporate interests rather than general internet users.

Low Earth Orbit satellite constellations like SpaceX’s Starlink offer the first genuine alternative to submarine cables for international communications. These systems could theoretically maintain global connectivity even during a complete submarine cable failure, though current satellite capacity remains far below cable capacity and costs significantly more.

The Race Against Time

The scenario of simultaneous global cable failure, while extreme, highlights the fragility of our interconnected world. Whether caused by coordinated military action, a major geological event, or cascading failures from localized damage, the loss of submarine cable connectivity would represent one of the most severe disruptions to modern civilization possible without direct physical destruction.

As our dependence on digital communications continues to grow, the question isn’t whether submarine cables will face major disruption, but whether we’ll build sufficient redundancy and alternative systems before such an event occurs. The clock is indeed ticking on one of modern civilization’s most critical vulnerabilities.