What we know about the Ukrainian strike on a Russian submarine in Novorossiysk

On 15 December 2025, Ukraine’s Security Service (SBU) claimed it hit a Russian Project 636.3 “Varshavyanka” (Improved Kilo-class) submarine while it was moored inside the naval base of Novorossiysk, using an underwater drone described as “Sub Sea Baby”. The SBU released video footage showing a large explosion close to a docked submarine; Reuters reported it independently verified the location shown in that video.

Another detail worth noting is the timing of Western ISR activity in the area. On 15 December we tracked a US Navy P-8A Poseidon conducting a prolonged orbit offshore of Novorossiysk, a pattern consistent with maritime ISR and signals collection rather than a simple transit. There is no open-source proof of a direct operational link between that mission and the subsequent underwater-drone strike, but the coincidence is striking: when a high-value incident unfolds around a major Russian naval hub, the presence of a P-8 loitering nearby is exactly the kind of indicator OSINT observers tend to flag as potentially relevant.

Meanwhile Russia’s Black Sea Fleet has denied that any ship or submarine was damaged, insisting the sabotage attempt failed.

From an OSINT angle, the biggest problem right now is not “did something happen?” (the geolocated footage strongly suggests it did), but “how bad was it?”. There is still no broadly accepted, independent visual confirmation that the submarine sank or that the hull suffered catastrophic damage below the waterline. Even specialist reporting that interprets the blast as occurring very close to the stern is, for now, based on released footage rather than post-strike, close-in imagery of the boat.

However, there is an additional detail that makes the “no damage” line increasingly hard to square with what’s visible in open sources. On 16 December, reporting based on satellite imagery (published via Radio Liberty and relayed by Ukrainska Pravda) showed clear damage to the pier in the exact area of the explosion, while noting the submarine remained alongside. The same reporting assessed the blast as occurring “several dozen metres” from the submarine, which implies that even if there was no clean, direct impact on the hull, the detonation was still close enough — and energetic enough — to plausibly cause underwater shock and fragmentation effects capable of damaging sensitive systems. In short: pier damage is not proof of a kill, but it is a strong indicator that the blast was real, powerful, and uncomfortably close to a high-value target.

Strategically, the reported strike matters because Novorossiysk has been treated as one of Russia’s more secure Black Sea Fleet hubs. If Ukraine can put an uncrewed underwater system into a defended naval base and detonate near a submarine at the pier, it reinforces a trend we’ve been tracking for months: rear-area “sanctuaries” in the Black Sea are becoming less and less sanctuary-like.