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Undersea cables carry the overwhelming majority of the world’s intercontinental data, but a single break usually does not switch off the internet. Operators reroute traffic around isolated failures; the serious danger is a cluster of breaks in the same corridor, combined with limited repair capacity and concentrated landing points.
That makes submarine-cable security a resilience problem rather than a prediction of an imminent global blackout. Routine fishing and anchoring accidents remain the main source of damage, while climate hazards, ageing infrastructure and unresolved sabotage allegations raise the consequences when several weaknesses coincide.
How much of the internet runs through undersea cables?
Submarine fiber-optic cables form the physical backbone of intercontinental connectivity. The International Telecommunication Union (ITU) said in 2026 that submarine telecommunication cables carry more than 99 per cent of data traffic worldwide.
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| Measure | Reported figure | Source and qualification |
|---|---|---|
| Worldwide data carried by submarine telecommunication cables | More than 99% | ITU, 2026; worldwide data traffic |
| Subsea-cable route length | More than 1.3 million km | JRC, 2025; electricity and data cables are included in the quoted Earth-spanning description |
| Active cables | Over 400 | JRC, 2025; definition differs from commercial-cable inventories |
| Commercial fiber-optic cables | 570 in service; 81 planned | Internet Society, 2025 policy brief |
What a submarine cable is and where it is vulnerable
A telecommunications cable is typically up to 4–5 centimetres in diameter. Optical fibers carry the signals; polyethylene, copper and, in some designs, steel-wire armour provide insulation, power conduction and mechanical protection. In deep water, cables generally rest on the seabed. Near coasts and in other shallow areas, they are commonly buried because human activity is more intense there.
That remote location makes the network difficult to patrol. A cable route may also converge with other cables at a landing station, then depend on a limited number of terrestrial links. The ITU identifies four connected resilience problems: high physical exposure, longer repair times, geographic concentration and dependence on a small number of systems. Small island developing states, least-developed countries and other underserved regions can have fewer alternatives when a route fails.
What usually damages the cables?
Most faults are accidental rather than deliberate. The JRC estimates about 150–200 accidental or unintentional subsea-cable damages each year. Fishing vessels are the leading cause. Bottom-trawling gear can reach cables at depths of up to 2,000 metres, while anchors more commonly damage cables in shallower water.
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| Cause | Evidence | Why it matters |
|---|---|---|
| Fishing activity or dragged anchors | 70–80% of faults | Estimate cited by the UK Parliament in 2025 from the European Subsea Cables Association |
| Other non-malicious factors | 20–30% of faults | Includes natural events and infrastructure wear, according to the same estimate |
| Natural and environmental damage | No single worldwide percentage stated | Earthquakes, volcanic activity, currents, sand-wave abrasion and fatigue can break or weaken cable |
| Ageing infrastructure | No single worldwide percentage stated | Older systems can add maintenance and failure risk |
The percentages are a baseline, not a forensic rule for every incident. The UK Parliament report says distinguishing a genuine accident from malicious intent is often difficult, especially before investigators have examined vessel movements, seabed evidence and the cable itself.
Would one cable cut take the internet down?
Usually, no. Network operators can automatically reroute traffic through other systems, so an isolated break may pass unnoticed by most users. The immediate symptoms can be a small capacity reduction or a modest increase in latency rather than a total outage.
The impact becomes serious when several cables share a corridor, a country has few independent systems, or the break also affects landing stations and onward terrestrial links. In those circumstances, users may see slower connections, congested routes, unstable international services and a regional outage that lasts far longer than a routine reroute.
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The defensible distinction is between local or regional degradation and a global shutdown. Existing evidence supports concern about capacity loss, latency and prolonged regional outages; it does not support claiming that any single cut will switch off the world.
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A real example: East Africa’s 2024 connectivity loss
The Internet Society’s East Africa report records damage to the SEACOM and EASSy cables off KwaZulu-Natal, South Africa, on 12 May 2024. Connectivity in multiple East African countries was significantly reduced. The cables were repaired by 3 June, approximately three weeks later.
The report attributes the suspected cause to a dragging ship anchor. Its broader lesson is redundancy: routes that appear separate on a map can still be exposed to the same maritime activity or landing-area constraint. A regional network with more genuinely independent paths has more capacity to absorb one failure.
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How long does submarine-cable repair take?
Repairs can take several weeks or, in difficult cases, months. A cable-repair vessel or submersible must locate the fault, obtain permission to work, recover the cable, splice in a replacement section, test it and return it to the seabed. The JRC says insufficient maintenance and repair vessels are a factor that can lengthen restoration.
Variables that set the timetable
- Location and depth: Deep-water faults require specialized equipment and longer vessel operations.
- Weather and sea conditions: Rough seas can suspend work or delay a vessel’s departure.
- Permits and diplomatic clearance: Repairs may cross national jurisdictions or protected waters.
- Vessel availability: A limited global repair fleet can create a queue after multiple incidents.
- Spare cable and equipment: Replacement sections and compatible parts must be available.
- Number of faults: Several breaks on one route require repeated recovery and testing operations.
The East Africa case gives a real-world reference point of about three weeks, not a universal service-level promise.
Are ships or countries cutting the cables?
Ships cause many documented breaks, but that does not by itself establish sabotage. Recent Baltic incidents have prompted concern about possible state-linked activity, while the JRC warns that some reported cases may have been accidental. The UK Parliament likewise says the overwhelming majority of faults are not malicious and that intent is hard to establish.
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There is no single authoritative worldwide statistic proving that sabotage is increasing. The accurate current description is that geopolitical attention has intensified and that attribution remains unresolved in many cases. Each incident should therefore be described in two separate parts: what is documented about the physical break, and what investigators have or have not established about who caused it.
How governments and operators can protect the backbone
Protect the seabed
Burial is the standard shallow-water defence. Rock placement and protective mattress coverings can add shielding where burial is impractical or seabed conditions demand another solution. These measures reduce accidental damage but cannot by themselves stop intentional interference.
Detect activity near routes
The JRC identifies radar, vessel-monitoring systems, automatic identification systems, aircraft patrols and satellite surveillance as complementary tools. Designated cable corridors with restrictions on fishing and anchoring can reduce routine risk when authorities can enforce them.
Design for rerouting
Route diversity matters more than a large cable count on paper. Operators and governments should assess whether paths are physically independent, whether they converge at the same landing station and whether terrestrial links can carry traffic after a marine break. The ITU’s 2026 roadmap calls for risk identification, monitoring, faster repair, greater redundancy and climate and environmental considerations.
Prepare for recovery
Resilience planning includes pre-positioned spare cable, maintenance agreements, trained crews, repair-vessel capacity and streamlined permits. The EU’s 2025 work maps infrastructure and applies risk assessments and stress tests, showing that cable security has become part of formal infrastructure planning rather than a matter left only to individual operators.
How to compare a cable-resilience strategy
| Question | What to examine |
|---|---|
| Route diversity | Are alternate cables genuinely separate, or do they share a corridor? |
| Physical protection | Is burial, rock placement or another method suitable for the depth and seabed? |
| Monitoring | Can authorities detect vessels and unusual activity around the route? |
| Landing and terrestrial concentration | Would one landing station or inland link become a bottleneck? |
| Repair capacity | Are vessels, crews, spare cable and compatible equipment available? |
| Coordination | Can permits and cross-border decisions be made quickly during a fault? |
| Regional equity | Does the plan protect vulnerable and underserved regions, not just major hubs? |
ITU Secretary-General Doreen Bogdan-Martin said on 10 July 2026 that the world relies on connectivity and that the International Advisory Body on Submarine Cable Resilience had produced a practical roadmap for keeping undersea networks reliable. The practical test of that roadmap will be whether it turns monitoring, route diversity and repair readiness into funded, coordinated capabilities before several failures occur at once.
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