China has brought online what is being described as the world’s first commercial underwater data center, according to a report published July 4, 2026 by the Spanish outlet OkDiario. The facility submerges sealed server modules in the ocean and uses the surrounding seawater as its cooling medium, an approach the report says sharply reduces the energy the facility consumes.

The report frames the launch as a template other coastal regions could adopt, naming Cartagena, Spain as the kind of Mediterranean port city where the model might be replicated. It does not disclose the operator, the facility’s capacity, or its precise location.

Executive Summary

The announcement matters because it moves underwater data centers from experiment to product. Submerging servers has been tested before — most famously by Microsoft — but a commercial deployment means paying customers are expected to run real workloads on seabed infrastructure, and that changes the questions from “does it work?” to “does it pencil out?”

The core appeal is cooling. Keeping servers from overheating is one of the largest energy costs in any data center, and the deep ocean offers a vast, stable heat sink at no mechanical-chilling cost. If seawater cooling delivers the efficiency the concept promises at commercial scale, it would arrive at a moment when AI-driven demand has made power and cooling the industry’s tightest constraints.

That said, the source report is brief and light on specifics. It attributes no capacity figures, energy metrics, customer names, or operator details. The launch is a genuine milestone in cooling infrastructure if the commercial framing holds — but the evidence available in this report is a claim of a first, not a documented performance record.

Why Put Servers on the Seabed?

Data centers spend an enormous share of their electricity not on computing but on removing the heat that computing generates. The industry measures this with PUE — power usage effectiveness, the ratio of total facility power to the power that actually reaches IT equipment. Conventional air-cooled facilities need chillers, fans, and often large volumes of water to hold safe temperatures, and in hot climates that overhead climbs steeply.

The ocean solves the problem passively. Below the surface, water temperature is low and remarkably stable year-round, and water conducts heat far better than air. A sealed capsule on the seabed can reject heat directly into an effectively unlimited sink, eliminating most mechanical cooling. Subsea deployment also removes evaporative water consumption — a growing point of friction between data centers and the communities that host them — and seabed real estate near dense coastal cities is not competing with housing or industry the way urban land is.

From Microsoft’s Experiment to Chinese Commercialization

The concept is not new; the commercial claim is. Microsoft’s Project Natick sank a sealed server vessel off Scotland’s Orkney Islands from 2018 to 2020 and reported that the submerged servers failed at a fraction of the rate of an equivalent land-based control group — likely because the nitrogen-filled, human-free capsule eliminated oxygen corrosion, humidity swings, and accidental knocks. Microsoft judged the experiment a technical success but never turned it into a product. China, meanwhile, has been running underwater data center pilots off its own coast for several years, so a progression from pilot to commercial service there is consistent with the trajectory — even though this report does not name the company involved.

If the commercial characterization is accurate, China would be first to market with a technology a US hyperscaler proved and shelved. That is a familiar pattern in infrastructure: the economics that don’t fit one company’s portfolio can fit another market’s constraints, particularly where coastal land, grid capacity, and water for cooling are all scarce at once.

The Hard Economics of Subsea Capacity

The obstacles are as real as the appeal. A submerged module cannot be serviced by a technician; a failed component stays failed until the entire vessel is raised, which pushes operators toward redundant hardware and infrequent, expensive retrieval cycles. Marine engineering, corrosion-resistant housings, subsea power and fiber connections, and specialized deployment vessels all add capital cost that the cooling savings must repay. Insurance, uptime guarantees, and repair logistics for seabed assets are largely uncharted territory for enterprise customers used to walking their auditors through a facility.

Environmental questions also need honest accounting. Rejecting heat into the ocean is thermodynamically unavoidable here, and while small-scale trials such as Natick reported minimal localized warming, the effect of dense clusters of commercial modules on marine ecosystems is site-specific and largely unstudied. Coastal permitting regimes — fisheries, shipping lanes, protected habitats — will shape where this model can actually go, and the report offers no detail on how the Chinese deployment cleared those hurdles.

Could Cartagena Be Next?

The report’s suggestion that coastal cities like Cartagena could follow is speculation, not an announced project, and it is worth being clear about that distinction. Still, the logic of the shortlist is sound: Mediterranean port cities combine dense populations that want low-latency services, constrained urban land and grids, warm climates that make conventional cooling expensive, and immediate deep water. Those are precisely the conditions under which subsea capacity is most competitive against land-based builds.

For European adoption, the gating factors would be EU environmental review, marine-spatial-planning approvals, and — not least — the geopolitics of importing a Chinese-proven infrastructure model into European digital sovereignty debates. Any operator pursuing it would more likely license the concept or develop it independently than deploy Chinese-operated modules in EU waters.

Background

Underwater data centers trace to Microsoft’s Project Natick, which began with a proof-of-concept in 2015 and culminated in a sealed vessel of several hundred servers operating off Scotland from 2018 to 2020. The retrieved servers had failed at a small fraction of the rate of an identical land-based group, validating the reliability case — but Microsoft ended the program without a commercial product. China picked up the thread with coastal pilot deployments in the years that followed, pursuing subsea capacity as an answer to scarce coastal land, strained grids, and the water consumption of conventional cooling.

The timing is not incidental. By 2026, explosive AI demand had made electricity and cooling the data center industry’s defining bottlenecks worldwide, pushing operators toward liquid cooling, novel sites, and any design that cuts overhead energy. A commercial subsea launch is China staking a claim to one of those frontiers first.

Source: China just switched on the first underwater data center, cooling servers with the ocean to slash energy use, and coastal cities like Cartagena could be next — OkDiario report, July 4, 2026, on China’s launch of the first commercial seawater-cooled underwater data center.

Researchers in China have reported a hollow-core optical fiber trial carrying 51.3 terabits per second over 128 miles (roughly 206 kilometers) without signal regeneration, according to a report published by Tom’s Hardware on June 28, 2026. The result is framed as a milestone targeting the networking bottlenecks created by the AI era’s explosive demand for data movement.

Executive Summary

The headline achievement combines three things that have historically been difficult to deliver at once in hollow-core fiber: very high aggregate capacity (51.3 Tb/s), meaningful terrestrial distance (128 miles), and the absence of signal regeneration — the electronic or optical boosting stations that long-haul links normally require. Hollow-core fiber guides light through an air-filled channel rather than solid glass, and its traditional weakness has been signal loss over distance. Demonstrating a multi-terabit link at this reach without regeneration attacks that weakness directly.

Why it matters: AI training and inference clusters are increasingly distributed across multiple data centers, and the links between those facilities are becoming a first-order design constraint alongside power and cooling. Hollow-core fiber promises both lower latency — light travels faster through air than through glass — and headroom for higher optical power, which together address exactly the bottleneck the report cites. A credible long-distance, high-capacity trial from China also signals that the hollow-core race is now genuinely global, not a Western-led curiosity.

Why Hollow-Core Fiber Is Suddenly Strategic

Conventional optical fiber sends light through a solid glass core. That works remarkably well, but it imposes two physical taxes. First, light moves about a third slower through glass than through air, which adds latency on every mile of a route. Second, intense light interacting with glass produces nonlinear distortions that cap how much optical power — and ultimately how much data — a single fiber can carry. Hollow-core fiber replaces the glass core with a precisely engineered air channel, so light travels faster and interacts far less with the material around it. For latency-sensitive users (financial trading was the earliest adopter) and for operators trying to push more terabits through existing conduit, those properties are directly monetizable.

The AI buildout has sharpened the case. Training runs increasingly span multiple data centers because no single site can secure enough power, and inference traffic is pushing metro and regional networks harder. When facilities tens or hundreds of miles apart must behave like one computer, every microsecond of round-trip time and every terabit of cross-site bandwidth counts. That is the ‘AI-era networking bottleneck’ this trial is aimed at, and it is the same logic that has driven hyperscaler interest in the technology in the West.

What 51.3 Tb/s Over 128 Miles Actually Demonstrates

The historically fatal flaw of hollow-core fiber was attenuation: early designs lost signal so quickly that links of even a few miles were impractical. Recent generations of antiresonant designs have brought loss down toward — and by some published accounts below — that of conventional fiber, but most headline demonstrations have involved either short distances, modest capacities, or laboratory spools rather than realistic spans. A 128-mile unregenerated link at 51.3 Tb/s, if borne out in the technical details, would indicate loss and signal-quality performance good enough for real regional routes, such as links between data center campuses or metro areas, without intermediate amplification stops.

The caveats matter, though. A trial is not a product. The report, as circulated, does not detail whether the fiber was deployed in field conditions or tested on spooled fiber in a controlled setting, what error rates were achieved, or how many wavelength channels produced the aggregate figure. These distinctions separate a genuine deployment milestone from a strong laboratory result, and the source material does not settle them. Both readings are consistent with what has been reported.

A Global Race, Not a Western One

Hollow-core fiber development has been most visibly associated with Western efforts — notably UK-rooted research that led to commercial deployments by a major US hyperscaler in its own network. A prominent Chinese result at this scale confirms that the technology is now a field of international competition, with implications beyond engineering. Optical fiber and the components around it (amplifiers, transceivers, cabling) are strategic supply-chain items, and nations building sovereign AI infrastructure have every incentive to develop domestic capability in next-generation transmission. For the broader market, competition tends to accelerate maturation and push down costs; for individual vendors, it compresses the window in which early leadership can be converted into commercial advantage.

The Road From Trial to Deployed Network

Even accepting the result at face value, several hard steps stand between a record trial and hollow-core fiber as routine infrastructure. Manufacturing hollow-core fiber at volume, with consistent quality and at a cost that competes with mass-produced conventional fiber, remains an industry-wide challenge. Field practicalities — splicing, connecting hollow-core to conventional fiber at network boundaries, cabling that protects the delicate microstructure, and keeping moisture and contaminants out of the air core — all add cost and complexity that trials rarely capture. Operators will also weigh whether the latency and capacity gains justify overbuilding routes that already have serviceable conventional fiber. The most likely early market is exactly where this trial points: new, high-value routes between AI data centers, where latency and bandwidth translate directly into compute efficiency and where builders are already spending at unprecedented levels.

Background

Hollow-core fiber has been researched for decades, but for most of that history its high signal loss confined it to niche, short-distance uses. A wave of design breakthroughs in the 2010s and 2020s — particularly antiresonant fibers that guide light in an air core surrounded by carefully arranged glass membranes — cut attenuation to levels approaching, and by some published accounts surpassing, conventional fiber. That progress turned commercial: Microsoft acquired hollow-core specialist Lumenisity in 2022 and has since deployed the fiber in parts of its own network, citing latency and capacity benefits for cloud and AI workloads.

The demand backdrop is the AI infrastructure buildout. As training clusters outgrow single facilities and inference traffic scales, data-center interconnect — the high-capacity links between sites — has become a critical constraint alongside power and cooling. That is the market context in which a 51.3 Tb/s, 128-mile unregenerated hollow-core trial, reported from China in June 2026, lands as more than a laboratory curiosity.

Source: China’s hollow-core fiber trial pushes 51.3 Tb/s over 128 miles without signal regeneration — milestone targets AI-era networking bottlenecks — Tom’s Hardware report, June 28, 2026, on a Chinese hollow-core optical fiber transmission trial.

The United States and allied governments have issued a joint warning that hackers linked to the Chinese state are disguising cyberattacks by routing them through “covert network” botnets — fleets of compromised internet-connected devices that make hostile traffic appear to come from ordinary, innocuous sources. The warning, reported by Cybersecurity Dive on April 22, 2026, represents a coordinated, multi-government attribution effort rather than a single agency’s finding.

Executive Summary

A joint advisory from US and allied cybersecurity authorities alleges that China-linked threat actors are using covert botnet infrastructure to obscure the origin of state-directed intrusions. A botnet is a network of hijacked devices — often home and small-office routers, cameras, and other poorly secured edge equipment — that attackers control remotely. Used as relay infrastructure, a botnet lets an attacker’s traffic emerge from residential and business IP addresses in the victim’s own region, rather than from servers traceable to a foreign operator.

The significance is twofold. First, joint multi-nation attribution advisories are deliberate diplomatic and defensive instruments: governments generally publish them only when the evidentiary picture is strong enough to share and the activity is serious enough to warrant public exposure. Second, the technique described strikes at a core assumption of network defense — that malicious traffic looks foreign or anomalous. When an attack arrives via a compromised router in a nearby suburb, geographic blocking and IP-reputation filtering lose much of their value.

For operators of data centers, networks, and critical services, the practical message is that perimeter trust based on source address is increasingly unreliable, and that unmanaged edge devices — anyone’s edge devices — are now strategic assets in state conflict.

Why Botnet Relays Defeat Traditional Defenses

Most network defense still leans on reputation: block traffic from known-bad IP ranges, flag connections from unexpected countries, trust what looks local. Covert relay botnets invert that model. By proxying attacks through thousands of compromised consumer and small-business devices, an operator makes each intrusion attempt appear to originate from a legitimate residential ISP address — often in the same country, sometimes the same city, as the target. Each device may be used briefly and then rotated, so blocklists chase addresses that are already abandoned.

The advisory’s framing — a “covert network” — suggests infrastructure built for stealth and persistence rather than the noisy, high-volume botnets historically used for spam or denial-of-service floods. That distinction matters: a quiet relay network is harder to detect precisely because it is not doing anything visibly disruptive most of the time.

Attribution as Policy: What a Joint Advisory Signals

Public, multi-government attribution is a comparatively recent tool of statecraft. When several allied agencies sign a single document naming a state actor, they are doing three things at once: sharing technical indicators with defenders, imposing reputational cost on the accused state, and signaling to their own critical-infrastructure sectors that the threat is assessed as serious at the national level. Beijing has consistently denied involvement in state-sponsored intrusion campaigns, and readers should note that public advisories typically summarize conclusions rather than publish the full underlying evidence — a genuine limitation of the format, even when the analysis behind it is extensive.

The pattern is nonetheless consistent with several years of Western advisories describing China-linked groups that favor stealth, living-off-the-land techniques (using a system’s own legitimate tools rather than detectable malware), and pre-positioning inside critical infrastructure rather than immediate disruption.

The Edge-Device Problem Nobody Owns

Covert botnets exist because the internet’s edge is saturated with devices that are unpatched, unmonitored, and often past end-of-support: home routers, IP cameras, network-attached storage, VPN appliances. No single party is accountable for them — consumers don’t patch, many vendors stop shipping updates, and ISPs have limited visibility into customer equipment. That accountability gap is now a national-security externality: every neglected router is potential relay infrastructure for someone else’s intelligence service.

Expect this advisory to add momentum to policy efforts around device security — secure-by-design commitments, software support lifecycles, and labeling schemes — because the demand side of the covert-network economy can only be constrained by shrinking the supply of hijackable devices.

What Infrastructure Operators Should Take From This

For enterprises, carriers, and data-center operators, the actionable lesson is architectural: treat source IP address as weak evidence of anything. Defenses that hold up against relay networks are behavioral and identity-based — anomaly detection on authentication patterns, phishing-resistant multi-factor authentication, network segmentation that limits lateral movement, and logging rich enough to reconstruct an intrusion after the fact. Operators of fleets of edge equipment — including hosting and connectivity providers — also sit on the other side of the problem: their unmanaged or end-of-life gear can become part of the covert network itself, making patch discipline and device retirement a matter of ecosystem hygiene, not just self-protection.

Background

Public attribution of state-sponsored cyber operations has become a standard instrument of Western policy over the past decade, with the US and partners such as the UK, Canada, Australia, and New Zealand increasingly issuing joint advisories rather than unilateral statements. Since 2023, a series of such advisories has focused on China-linked groups accused of infiltrating critical infrastructure using stealthy techniques, including botnets built from end-of-life routers used as relay infrastructure. China has denied these allegations throughout.

The underlying enabler is the enormous installed base of consumer and small-business network devices that receive few or no security updates. Security researchers have long warned that this unmanaged edge constitutes ready-made anonymization infrastructure for any sophisticated actor willing to compromise it at scale.

Source: China disguises cyberattacks with ‘covert network’ botnets, US and allies warn — Cybersecurity Dive report on a joint US-allied advisory, April 22, 2026.