Ukraine’s Security Service (SBU) said on Monday that it had struck a Russian Kilo-class submarine at the Black Sea port of Novorossiysk using an underwater “kamikaze” drone, publishing video of a large underwater blast near a pier where vessels were berthed.

Reuters said it verified the location of the footage by matching the port’s layout and piers. Ukraine said the operation disabled the submarine and described the attack as the first time an underwater drone had neutralised a submarine. Russian officials did not immediately comment publicly, according to Reuters.

The SBU said the strike used a system it calls “Sub Sea Baby”. The target was a diesel-electric Kilo-class attack submarine, a type used by Russia’s Black Sea Fleet. The submarine was a Varshavyanka-class boat, a Kilo-class variant, and that it carried four launchers for Kalibr cruise missiles.

Ukrainian officials have presented the strike as aimed at reducing Russia’s ability to launch Kalibr missiles from the sea. Reuters described Kalibr as a mainstay of Russia’s long-range attacks and said the submarine is capable of carrying at least four such missiles.

A strike inside Russia’s main Black Sea base

Novorossiysk, in Russia’s Krasnodar region, has grown in importance for the Russian navy as Ukraine has expanded attacks on Russia’s Black Sea Fleet. Russia has rebased many vessels there to keep them beyond the reach of Ukrainian strikes in Crimea.

Ukraine’s ability to contest Russian naval activity has relied heavily on uncrewed systems. Ukraine, which has “practically no naval fleet left”, has used sea drones and missiles to push Russian ships away from Sevastopol, the Black Sea Fleet’s traditional hub in occupied Crimea.

The SBU described the Novorossiysk strike as a joint operation involving the SBU and the Ukrainian Navy, and linked it to earlier damage inflicted on Russian vessels by Ukrainian surface drones.

What is “Sub Sea Baby” and what might Ukraine have used?

Ukraine has not released technical specifications for the underwater system used in the Novorossiysk operation beyond the name and basic description. “Sub Sea Baby” was presented as an underwater variant of the SBU’s “Sea Baby” naval drone programme.

Ukraine’s security service had unveiled an upgraded Sea Baby sea drone capable of operating across the Black Sea, with heavier payload options and the use of artificial intelligence for targeting.

In parallel, Ukrainian media and defence outlets have reported on another family of Ukrainian uncrewed underwater vehicles, “Toloka”, with published ranges and payloads that, in theory, could support long-distance missions. Toloka models include a TLK-400 with a range up to 1,200 km and payload up to 500 kg, and a TLK-1000 with a range up to 2,000 km and payload up to 5,000 kg. Ukraine has not said whether any Toloka variant was involved in the Novorossiysk strike.

Verification and likely consequences

Independent confirmation of the submarine’s condition remains limited. The Ukrainian claim is that the submarine has been put out of action; Ukraine’s navy spokesman described the operation as a “turning point” and argued that repair would be difficult because it would have to be conducted above water, exposing the boat to further attack.

Russia had four submarines based at Novorossiysk, three of them capable of launching Kalibr cruise missiles. Ukraine says one of those boats has now been put out of action.

The strike comes amid US-brokered talks in Berlin on possible settlement terms. Ukraine has sought to demonstrate it can inflict significant damage on Russian forces, particularly after comments by US President Donald Trump about Ukraine’s negotiating position.