In early March, engineers, soldiers and defense firms gathered at a windswept training ground in Latvia for a new kind of experiment. The exercise, run under NATO’s Innovation Range initiative, focused on countering aerial drones. But just as important was what wasn’t in the sky.

It was in the water.

While the first Testing, Evaluation, Verification and Validation (TEVV) campaign at the Sēlija Military Training Area targeted unmanned aircraft systems, it is part of a broader network of ranges, including sites dedicated to underwater systems in Italy and shallow-water autonomy in the Netherlands, that point to a strategic shift. NATO isn’t just preparing for drone warfare above ground. It is racing to understand it below the horizon line.

In the span of just a few years, uncrewed surface vessels (USVs) have moved from experimental curiosities to operational weapons with strategic impact. Recent attacks on oil tankers in the Gulf—widely attributed by analysts to explosive-laden naval drones demonstrate how low-cost systems can threaten critical shipping lanes. These incidents echo earlier battlefield lessons from Ukraine, where maritime drones were used to damage and sink larger, more expensive warships.

Navies are responding, but not yet comfortably. During Exercise Cobra Gold 2026 in Thailand, forces from the United States and partner nations trained against swarming maritime drones using systems like the Hammerhead USV target provided by QinetiQ. The exercise simulated multiple threat profiles, including coordinated swarm attacks designed to overwhelm ship defences and disrupt commercial shipping. Ten drones, controlled from both land and sea, replicated explosive attack craft closing in from multiple directions.

What worries planners is not just the existence of these drones, but their scalability. A navy can intercept one incoming threat. Ten becomes harder. Fifty begins to resemble saturation.

If maritime drones were simply smaller versions of traditional threats, the challenge would be manageable. But they are not.

They are harder to detect, often riding low in the water with minimal radar signature. They can be remotely piloted, pre-programmed, or increasingly autonomous. In some cases, as demonstrated in multinational exercises led by Ukraine, defending forces did not even detect the incoming systems before simulated impacts. That failure mode is what keeps naval planners awake.

Industry is moving quickly to industrialize maritime drones. Companies like Anduril, in partnership with Hyundai Heavy Industries, are developing modular autonomous surface vessels designed for rapid production and flexible missions. The concept mirrors trends in aerial drones: open architectures, interchangeable payloads, and scalable manufacturing. A single platform might conduct surveillance one week and carry strike payloads the next.

Unlike legacy warships, which take years to build and enormous budgets to sustain, maritime drones can be produced in volume, adapted quickly, and deployed in contested environments without risking crews. Quantity, in this case, has a quality all its own.

What makes maritime drones especially potent is their integration into a wider ecosystem of autonomous systems. Surface drones can coordinate with aerial drones for targeting. Underwater vehicles can operate beneath them, gathering intelligence or laying the groundwork for future strikes. Electronic warfare payloads can disrupt communications and navigation systems, compounding the chaos.

NATO’s innovation ranges reflect this reality. The separation between air, surface and subsurface domains is eroding. Testing environments are being designed not around individual systems, but around interactions between them. In future conflicts, a naval commander may not face a missile or a submarine, but a network.

Military ships are not the only targets. The attacks on oil tankers in the Gulf highlight a broader vulnerability: global shipping. Maritime drones are uniquely suited to target slow-moving, high-value commercial vessels in chokepoints like the Strait of Hormuz. Even a single successful strike can have outsized economic effects. Disruptions to shipping lanes ripple through energy markets, insurance costs and global supply chains.

Back in Latvia, NATO’s focus on counter-drone systems may seem air-centric at first glance. But the same principles, detection, electronic warfare, layered defense, also apply at sea. Future naval exercises are increasingly incorporating mixed drone threats, combining aerial and maritime systems in coordinated scenarios. The goal is to build defences that can handle complexity, not just individual platforms.

But there is a gap.

Unlike aerial drones, where countermeasures are rapidly maturing, maritime drone defense remains uneven. Sensors struggle with cluttered sea environments. Rules of engagement for commercial areas are unclear. And the sheer cost imbalance remains unresolved.

For decades, naval power was defined by large platforms: aircraft carriers, destroyers, submarines. Maritime drones are not intended to replace these assets, but they do change how they operate and how vulnerable they are.

A billion-dollar warship can now be threatened by a system that costs a fraction of that price. That asymmetry is driving urgency across alliances, industries and navies. NATO’s expanding network of innovation ranges is one response. Multinational exercises like Cobra Gold are another.

But the pace of change suggests something deeper.

Maritime drones are not just another capability. They are a forcing function, pushing navies to rethink detection, defense, and even the meaning of control at sea. The oceans are not getting quieter. They are getting smarter.

And far more dangerous.