The Ukrainian naval drones, developed largely through crowdfunding and volunteer engineering efforts early in the war, operate at waterline level, making radar detection difficult. They can loiter for extended periods, approach targets slowly to avoid creating distinctive wakes, and carry explosive payloads equivalent to several hundred kilograms of TNT.

NATO naval commanders requested Ukrainian participation in the exercise specifically to test alliance defenses against such threats, according to defense officials speaking on background. The results proved sobering. The frigate—whose nationality was not disclosed in the reporting, likely for diplomatic reasons—deployed standard countermeasures but failed to detect the approaching drones until exercise controllers declared the vessel "sunk."

The implications extend far beyond Europe. US naval forces operating in the Persian Gulf face similar threats from Iranian forces, who have developed their own maritime drone capabilities. The Houthi movement in Yemen has employed unmanned boats against vessels in the Red Sea. Traditional naval powers suddenly find expensive warships vulnerable to weapons costing a fraction of their targets' value.

Ukrainian President Volodymyr Zelensky, who announced Tuesday that Kyiv has deployed 201 drone specialists to the Middle East, has emphasized the asymmetric advantage such systems provide. In separate remarks, he noted that Ukraine downs drones for approximately $10,000 while American forces employ $4 million missiles—a cost disparity that applies equally to offensive operations.

The Portuguese exercise suggests navies must fundamentally rethink defensive postures. Traditional task force formations, designed to provide layered defense against aircraft and submarines, leave gaps exploitable by small surface craft. Close-in weapon systems, the last line of defense on modern warships, struggle to engage multiple small targets simultaneously.

Russian naval forces learned these lessons through bitter experience. The Black Sea Fleet, once dominant in regional waters, now operates primarily from Novorossiysk, more than 200 miles from Ukrainian drone launch sites. Multiple vessels, including landing ships critical for amphibious operations, were sunk or damaged in port by Ukrainian attacks that penetrated harbor defenses.

NATO is reportedly accelerating development of countermeasures, including acoustic detection systems, rapid-fire cannon designed for small-boat threats, and drone-vs-drone interception methods. But the Portuguese exercise demonstrates that current capabilities remain insufficient against determined attacks by operators who understand naval blind spots.

The exercise also revealed organizational challenges. Modern warships deploy sophisticated sensor suites, but crews trained for conventional threats may not recognize small craft as imminent dangers until too late. Human factors—watchstanders focused on air and subsurface threats—proved as significant as technical limitations.

As maritime drone technology proliferates, the Ukrainian example provides a template for any actor seeking to challenge conventional naval power. The barriers to entry remain remarkably low: commercial components, open-source software, and basic explosives can produce weapons capable of threatening billion-dollar warships. Whether NATO adapts quickly enough to counter this asymmetric threat may determine the outcome of future conflicts at sea.