Undersea Cable Security in the Indo-Pacific Starts With Vessel Behavior

At a Glance

• Hawaii and Guam concentrate Pacific undersea cable risk, and Honolulu sits directly on that infrastructure.
• Most cable faults are accidental, so a damaged cable alone says little about intent.
• Behavioral history is what separates routine traffic near a cable route from activity that warrants attention.
• With few specialist repair ships in the region, early warning is the most practical form of undersea cable security.
• All-source intelligence gives decision-makers the picture before the fault.

Undersea Cable Security in the Pacific Runs Through Hawaii and Guam

Undersea cable security in the Indo-Pacific comes down to a handful of islands. Hawaii and Guam anchor the trans-Pacific links that connect the continental U.S. to its forces, allies, and partners across the theater. Honolulu itself sits on that infrastructure.

The exposure is measurable. In Q1 2026, Windward recorded 27 slow-speed service and research vessel events near cable routes around Hawaii and 5 around Guam and the Northern Marianas, in a U.S.-connected cable region where research and survey vessels made up 13.4% of activity. A September 2026 report for the U.S.-China Economic and Security Review Commission found that continental U.S. connections to Hawaii and Guam are particularly vulnerable to gray-zone sabotage, with few redundancy options.

None of those events proves hostile intent. What they show is where to look. Cable protection is decided long before a fault, by knowing which vessels are doing what near the cable route. That takes intelligence, not tracking alone.

Pacific Cable Hubs Concentrate Risk in a Few Places

Geography makes the Pacific cable network efficient and fragile at the same time. Hawaii and Guam host landings for trans-Pacific systems linking the continental U.S. with Asia, and a report found that the continental U.S. connections to both have few redundancy options.

Guam shows the pattern in miniature. The island was the landing point for 11 subsea cables as of 2023, and every landing site sat on its western coast. Clustering keeps costs down for operators. It also means one incident in the shallow approaches to those landings can touch several systems at once.

The U.S.-China Economic and Security Review Commission report modeled what that concentration means for capacity. Disruption to even a single cable could overwhelm available capacity on direct routes between the U.S., Taiwan, Japan, and the Philippines, forcing traffic onto slower and less direct paths. Several cables cut together could overwhelm trans-Pacific capacity as a whole.

For a joint force that relies on those links for command and control, logistics, and coalition coordination, that is an operational problem, not a telecom one.

Most Damage Is Accidental, Which Makes Intent Hard to Read

Most undersea cable damage has nothing to do with sabotage. A March 2026 CSIS analysis of Indo-Pacific cable frameworks notes that the majority of faults come from natural disasters, fishing, and genuine maritime accidents. Windward’s Q1 2026 Undersea Cables Risk Report reaches the same conclusion from vessel data, ranking trawlers as the highest-priority accidental damage risk because their steel ground gear and weighted otter boards can snag, drag, or sever a cable.

That baseline is exactly what makes intent hard to read. CSIS points out that a deliberate cut is low probability but high impact, and that the sheer volume of accidental damage gives a malicious actor plausible deniability. A sabotage event can hide inside the statistics.

Taiwan shows how this plays out. In February 2025, Taiwan’s coast guard detained HONG TAI 58, a Togo-flagged cargo vessel with a Chinese crew, after a cable to the Penghu Islands was disconnected near where the ship had dropped anchor. Prosecutors charged its captain in April 2025. 

By then, Taiwan had reported five cases of seabed cable damage in 2025, compared with three in each of 2023 and 2024. That same month, INDOPACOM commander Adm. Samuel Paparo acknowledged to lawmakers that there had been attempts to sabotage undersea cables, particularly around Taiwan.

The takeaway for undersea cable protection is that the fault itself is weak evidence. An anchor drag looks the same on the seabed whether it came from negligence or a decision. What differs is everything the vessel did before it reached the cable.

Vessel Behavior Separates Routine Traffic From Cable Risk

Not every vessel near a cable route is a concern, and treating them all the same buries the signal. Windward’s cable reporting separates two categories of risk that can show up on the same stretch of seabed.

The first is slow-speed activity by service and research vessels, defined as holding slow speed for more than an hour near a known cable route. Some of it is legitimate repair, survey, or scientific work. It warrants closer scrutiny when the vessel is flagged to, operated by, or affiliated with a state of concern, or sails under a flag of convenience that obscures ownership, and especially when that combines with repeated activity or extended presence. The second is fishing and trawling, where the risk is physical and usually accidental.

The Pacific shows why the distinction matters. In Q1 2026, the region logged only 19 state-of-concern service vessel events, all Chinese or Russian, yet 20% of its cable-proximate activity lasted longer than 24 hours, the highest extended-presence rate of any region. On the fishing side, the Pacific recorded just 12 trawler events. More than half of Pacific fishing activity, 54.4%, came from Chinese-flagged vessels operating around Kiribati, the Solomon Islands, and Fiji, all of which host landing stations tied to U.S. Pacific communications.

A single position report cannot tell these patterns apart. A survey vessel at four knots and a fishing vessel at four knots look the same in one snapshot. The difference shows up over time.

A recent case near Guam shows what that looks like. From August 31 to approximately September 20, 2026, a Chinese-flagged fishery patrol vessel ran a grid east of Guam between the Bulikula and SEA-US cables. After crossing the Guam and CNMI EEZ from September 20 to 22, it started a second grid west of Guam in the Philippine Sea, still running as of September 29. On September 13, it met a Cook Islands-flagged tanker for about six hours, likely to refuel, which let it stay at sea. Its AIS stayed on throughout.

Read as a string of position reports, this is a fishery patrol vessel at sea. Read against its behavioral history, the picture changes. This was the first time the vessel had done this kind of activity in the region, since it usually operates around China and occasionally in the Indian Ocean. Its north-to-south legs and repeated slow-speed stops match a survey pattern, not a patrol or a transit. Windward analysts assessed the activity as consistent with possible mapping of the seabed and cables around Guam. That is a risk indicator worth tracking, not proof of intent.

Behavioral history lets an analyst read a vessel’s activity against its own past and the past of its ownership network. None of these indicators proves intent. Each one tells a watch floor where to point the next sensor.

Thin Repair Capacity Makes Early Warning the Real Defense

Repair is the slowest part of undersea cable protection. A May 2025 RSIS commentary, citing the International Cable Protection Committee, counts just 16 specialist repair vessels based in the Indo-Pacific. Around 200 cable faults occur worldwide each year, and roughly two-thirds of them are caused by ships. The same commentary notes that a 2024 repair to the SEA-ME-WE 5 cable was held up for two months by permitting rules alone.

The fleet is not growing to match demand. CSIS counts 62 vessels globally that lay and maintain cables, only 19 of them contracted for maintenance, and notes that new cable ships are not entering service as fast as old ones retire. The forecasts it cites expect cables in the Southwest Pacific to need 141 repairs in 2040, nearly half of all faults worldwide. The USCC report describes global repair fleets as aging and thinly stretched.

The arithmetic points one way. When a fault can take weeks to clear and the ships that clear it are shared across an ocean basin, the most useful defense is knowing which vessels are working near the route before anything breaks. Adm. Paparo made a similar point in his April 2025 testimony, naming intelligence that gets inside an adversary’s targeting chain, and the presence that follows it, as the first countermeasure to cable sabotage.

All-Source Operational Intelligence Gives Decision-Makers the Picture Before the Fault

Tracking tells you where a vessel is. Intelligence tells you what it is doing and whether that should change your next decision. Undersea cable security depends on the second.

AIS alone cannot carry that load. It is self-reported, it can be switched off, and vessel identities can be manipulated. Windward’s Q3 2026 Maritime Risk Report shows how far that has gone. The IMO’s list of falsely flagged ships reached 613 by the end of September, up 39% since January, and 84 dark fleet tankers changed MMSI numbers to reflag to Russia in a single quarter.

The broadcast picture also misses whole streams of traffic. In the Strait of Hormuz, Windward estimates that 52% of September transits were invisible to AIS and satellite observation, measured as the gap between UKMTO’s total count and visible traffic.

If half of a chokepoint’s traffic can drop out of view, so can a single vessel working slowly over a cable. All-source operational intelligence closes that gap by fusing AIS with SAR and EO satellite imagery, RF detection, and years of behavioral history, as well as any other source that sharpens the picture. Every vessel is then read against its ownership network and the cable routes beneath it.

For a watch floor at INDOPACOM or a component command, that changes the question. Instead of asking what broke and who was nearby, analysts can ask which vessels have started behaving differently near the Hawaii and Guam landings, which of them share owners or managers, and which have gone dark over a cable corridor. Those answers are early warnings, not verdicts. They give commanders time to cue a patrol, task an ISR asset, or alert the cable operator while the cable is still intact.

Written by Maya Romi, Windward Senior Maritime Intelligence Content Manager.