Necessity is famously the mother of invention, and there is no more pressing necessity than war. One other desideratum of warfare is surprise. And Ukraine, in its fight with its Russian invaders, has been good at invention and surprise, both separately and in combination.

One particular surprise was something that was washed ashore in September on the Crimean coastline near Sevastopol, the site of a naval base that is the home port of Russia’s Black Sea fleet. A photograph of it suggests something that looks like a large version of a hobbyist’s remote-controlled model boat. The cameras amidships and on the bow indicated that it may have been on a spying mission.

Intriguing. But then, late in October, came the sting. A fleet of the things, accompanied by aerial drones, attacked the Black Sea fleet at anchor. In the Ukrainian version of subsequent events, three vessels were hit and damaged, including the fleet’s replacement flag-ship, Admiral Makarov, the previous incumbent of that role, Moskva, having, in the words of a Ukrainian wag, been “promoted to submarine” by a more conventional attack using anti-ship missiles.

Is this the start of a new form of naval warfare? The world’s most serious naval powers—America, China, Britain, Israel and so on—have been experimenting with so-called Uncrewed Surface Vessels for about a decade. But these have mostly been missile- or gun-carrying boats rigged to operate under remote control. Kamikaze craft have been the province of irregular forces, such as the Houthi and Hamas.

The inventive military boffins of Ukraine have changed that. They have shown the effectiveness of fleets of kamikaze marine drones, unencumbered by human crew who might balk at running the gauntlet of machinegun fire that was directed at the drones when they were on their final attack run, which was gleefully posted online by Ukraine’s exceptionally effective propagandists.