Ukrainian naval drones ply the Black Sea with surface-to-air missiles, ready to shoot down enemy warplanes. They ferry aerial attack drones closer to targets. And this month, a Ukrainian drone was filmed in a drone-on-drone water battle with a Russian counterpart.

When Russia began its full-scale war against Ukraine, Moscow dominated the waterways. Kyiv scaled up its drone operations, eventually sinking about a third of Russia’s vaunted Black Sea fleet with what amounted to remote-controlled, exploding speedboats.

Now Ukraine is taking it a step further by establishing offshore layers of drone defense and offense, transforming naval warfare along the way.

New technologies arrive on the sea each month. In one instance, a drone boat deposited a four-wheeled, remote-controlled ground vehicle with a mounted machine gun on a Russian-occupied peninsula in what Ukraine called the first ever all-robot amphibious assault.

Remotely operated naval vessels are not unique to Ukraine. Yemen’s Houthi rebels used a drone boat in an attack on a Saudi frigate almost a decade ago. This summer, the United States used unmanned Corsairs to rescue a downed helicopter crew and to attack a naval installation. But Ukraine’s success in fighting a vastly larger Russian Navy is being studied by military planners from Taipei to Tallinn.

“Countries all over the world are looking to Ukraine as an example of how to use them in their own navies,” said Emma Salisbury, a senior fellow at the National Security Program of the Foreign Policy Research Institute.

Remote-controlled vessels are not a replacement for a traditional navy, said Sam J. Tangredi, a professor at the U.S. Naval War College. “Drones are tools in the tool kit,” he said. “They’re useful systems. They will be used in wars. They don’t change the equation.”

Still, the cheap, off-the-shelf nature of Ukraine’s drone flotilla means the barriers to entry are low for would-be defense contractors. Twenty-seven Ukrainian companies are experimenting with new naval platforms and technologies, testing different models and capabilities, which pushes innovation forward, according to Dennis Kanin, director of Ukraine’s Unmanned Naval Association, a trade group.

“For the cost of maintaining a single warship, with water drones you could provide security for a small country,” Mr. Kanin said.

Interest From Abroad

Ukraine’s sea-drone technology has caught the world’s attention. UFORCE, a company founded in Ukraine, recently struck a deal for a joint venture to begin production in the United States. The company makes Magura sea drones, the first kamikaze drones used by Ukraine.

The largest Norwegian defense company, Kongsberg, opened an office in Ukraine and started collaborating with Ukraine’s producer of Sargan sea drones. Other Nordic countries, Baltic countries and Japan have also proposed collaboration, Ukrainian entrepreneurs say.

“All these years, ever since maritime drones started sinking the Russian fleet, countries have been approaching us seeking to acquire these vessels for themselves or establish domestic production, including countries in the Persian Gulf,” said Kyrylo Budanov, Ukraine’s presidential chief of staff.

In March, President Volodymyr Zelensky said that Ukraine was negotiating with Gulf states over delivery of its naval drones, along with air defenses, though it is not clear where those deals stand now.

Unlike Kyiv, which is more than a hundred miles from the Russian border behind layers of air defense, coastal areas such as Odesa — or indeed Abu Dhabi or Dubai — have little warning before an attack with a Shahed, an Iranian-designed exploding drone. Basing air defenses at sea provides more time to detect and shoot down incoming drones.

“For the Gulf states, this could be extremely relevant,” said Oleksiy Honcharuk, a former Ukrainian prime minister and the chairman of UFORCE’s board. “The flight time of Shaheds to their targets is short, while they have many coastal cities and oil terminals located on the coast.”

For defense contractors and military planners, Ukraine’s technology offers advantages. Ukrainian systems are battle-tested, having operated under Russian fire in environments with no GPS signal. Also, Ukraine’s military and the defense start-ups supplying it have focused on inexpensive, easy-to-build drones, platforms that can be scaled up quickly.

“Instead of thinking of a B-52 flying for 75 years, you’re thinking of something where if you don’t use it in conflict year one to five, maybe you break them down to scrap and use them for a new mission,” said Cynthia R. Cook, senior fellow with the Center for the Industrial Base at the Center for Strategic and International Studies. “The smaller programs allow for faster refresh.”

Battle-Tested Technology

This new form of naval power began, like so many inventions, with a multitude of failures.

The first Magura drones were based on a civilian motorboat produced in Odesa. Ukrainians began testing the sea drones in the spring of 2023, and the drones have become more sophisticated over time.

“We would lose the drone, then go after it, tow it back, tinker with it, fix something, and it would happen again and again,” a commander with the call sign Thirteen said as his pilots tested sea drones at a secret location. He leads a sea drone unit run by Ukraine’s military spy agency, known as HUR.

On a scorching day this summer at a different training ground, another unit commander at the agency, known as Ninth, sat on a child’s swing beside a lake in central Ukraine. As the swing rocked gently, he watched the latest version of his technology carve the calm inland waters.

Both Thirteen and Ninth asked to be identified only by their call signs, in keeping with their agency’s rules.

The lake near where Ninth sat was a test site for drone boats that launch aerial drones, essentially miniature aircraft carriers, first used last year.

At the time, Ukrainian military planners were preparing an attack on the Russian seaports of Tuapse and Novorossiysk, Ninth said. The Russians had set up radar antennas on offshore oil platforms that were helping to identify incoming drone boats. The Ukrainians needed to take out those antennas in the opening phase of an assault.

Ninth realized that interceptor aerial drones could help. He could fit many on the deck of a three-and-a-half-ton Katran sea drone and use them to bombard coastal targets from sea — or, in this case, to hit an oil platform.

After dark, Ninth ordered the launch of his aircraft carrier drones, he said. They took off from the decks and buzzed toward their targets, guided by operators. The repurposed interceptors destroyed the antennas and killed the Russian soldiers operating them. With the radars taken out, other sea drones slipped through and attacked the Russian ports.

Another new use for the boats came in April this year when Ukraine’s 412th Unmanned Systems Brigade shot down two Russian Shaheds using interceptor drones launched from a water platform.