The money going into underwater defence technology is growing quickly, and the reason is a length of cable. More than 1.5 million kilometres of submarine communications cable was in service globally as of early 2026, according to TeleGeography, and almost none of it is watched.
"It's the changing threat environment that's brought this to the fore," Katja Bego, senior research fellow at Chatham House, told CNBC. Advances in autonomy, drones and machine learning have made continuous monitoring of the seabed plausible for the first time, which turns a known vulnerability into a fundable programme.
Nord Stream changed the risk assessment
The pivot point was September 2022, when explosions ruptured the Nord Stream gas pipelines under the Baltic months into Russia's full-scale invasion of Ukraine. Investigators concluded the damage was deliberate sabotage. Since then, subsea infrastructure has been damaged in the Arctic and near Taiwan.
Bego's description of the preceding decades is blunt: the seabed was neglected for a long time and there is a lot of catching up to do. That neglect was rational while it lasted. Subsea cables were treated as a commercial telecoms asset, protected by depth, obscurity and the assumption that no state would attack civilian infrastructure below the threshold of war.
Hybrid warfare removed that assumption. The term covers cyberattacks, energy sabotage, disinformation and economic pressure, applied with or without conventional force, and the appeal of a cable cut is precisely that attribution is slow and retaliation is awkward. An anchor dragged across a seabed is plausibly an accident for long enough to matter.
What is on the shopping list
The programmes being funded fall into two groups. One is detection: sensors attached directly to cables and pipelines, acoustic monitoring, and analysis that can distinguish a fishing vessel from something loitering. The other is presence: autonomous underwater vehicles that can patrol, inspect and respond without a crewed ship overhead.
Both benefit from the same shift that reshaped the war above the surface. Ukraine demonstrated what cheap autonomous systems operated from a distance can do to expensive platforms, and the underwater version of that lesson applies to both attack and defence. It is the same economics visible in a Swedish loitering munition running its target selection on a development board that costs a few hundred dollars. Capability that used to require a navy now requires a supplier.
The defensive side has the harder problem. The infrastructure is enormous, dispersed across international waters, and mostly privately owned. A cable operator's commercial case covers repair, not deterrence, and no single government has jurisdiction over a line that crosses six exclusive economic zones.
The exposure is bigger than telecoms
Alongside communications cable and oil and gas pipelines, there is a growing network of subsea power cable connecting electricity markets and bringing offshore wind generation to shore. That is a newer dependency and a more brittle one, because electricity cannot be rerouted the way packets can.
This is the seabed version of a problem already visible on land, where the equipment keeping the grid running was never designed to be defended and the operators carrying the cost are regulated utilities with thin margins. Interconnectors have the same structure: essential, expensive, and owned by companies whose business case does not include a hostile state.
For investors, the sector is early and the tailwind is durable. Defence budgets in Europe are rising with explicit lines for maritime domain awareness, and the buyers are governments rather than the commercial operators who cannot justify the spend. The caution is the usual one for defence technology: procurement cycles are long, demonstrations are cheap, and the gap between a working autonomous vehicle and a fielded programme is measured in years.