Ukraine’s Security Service (SBU) announced on Sunday that it had carried out a covert underwater strike against a Russian Improved Kilo-class diesel-electric submarine inside the heavily guarded naval base at Novorossiysk, marking a significant escalation in the maritime dimension of the war in the Black Sea.
According to the SBU, the operation was conducted jointly with Ukraine’s Naval Forces and the 13th Main Directorate of Military Counterintelligence. The attack reportedly employed a new unmanned underwater vehicle (UUV) known as the “Sub Sea Baby,” which struck the stern of the submarine while it was moored inside a submarine pen at the far end of the harbor.
The Russian Ministry of Defense quickly denied the claim, stating that Ukrainian forces failed to damage any vessels at the base. Independent verification of the extent of damage remains unavailable. However, video footage released by the SBU shows a powerful explosion at the aft section of a submarine consistent with the dimensions and layout of an Improved Kilo-class boat.
Extent of Damage Remains Unclear
The released footage appears to show the unmanned underwater drone detonating near the stern, an area that houses critical propulsion systems as well as vertical and horizontal dive planes. Naval analysts note that even if the submarine did not sink at its berth, damage to the pressure hull, propeller shaft, or control surfaces could render the vessel non-operational for months, if not longer.
Improved Kilo-class submarines are among the quietest non-nuclear submarines in service and form a core component of Russia’s Black Sea Fleet. They are capable of launching Kalibr cruise missiles from their torpedo tubes, weapons that have been used extensively against Ukrainian energy infrastructure, ports, and urban targets since the start of the invasion.
The SBU claimed that the targeted submarine was armed with Kalibr missiles at the time of the strike, though it remains unknown whether it was preparing for an imminent launch.
“Sub Sea Baby”: A New Phase in Naval Warfare
The attack introduces what Ukrainian officials describe as a new generation of maritime strike capability. The Sub Sea Baby drone is believed to be an underwater evolution of Ukraine’s earlier Sea Baby unmanned surface vehicles, which have successfully attacked Russian warships and tankers across the Black Sea since 2022.
Unlike surface drones, the Sub Sea Baby operates fully submerged during its attack run. This allows it to bypass floating barriers, booms, and other defenses designed to stop surface threats. Analysts assess that the system likely functions in a manner similar to an autonomous torpedo, navigating toward pre-programmed waypoints before switching to onboard sensors for terminal guidance.
Such a capability would explain how the drone was able to maneuver through the confined waters of Novorossiysk harbor, make multiple turns, and reach a submarine pen deep inside the base.
Whether the drone was fully autonomous or received real-time guidance remains unclear. The video released by the SBU appears to originate from fixed harbor surveillance cameras, raising the possibility that Ukrainian intelligence services had access to Russian monitoring systems. Notably, the footage shows vessels inside the harbor highlighted with green boxes, suggesting the use of automated or AI-assisted ship recognition software.
Renewed Escalation in the Black Sea
The reported strike comes amid a renewed phase of maritime escalation after several relatively quiet months. Until recently, Ukrainian attacks in the Black Sea region were largely limited to aerial drone strikes against Crimea and Novorossiysk, often targeting oil terminals and energy infrastructure.
In late November and early December, Ukraine shifted focus toward Russia’s so-called “shadow fleet” of oil tankers used to circumvent international sanctions. On November 28, Ukrainian maritime drones struck the tankers Virat and Kiaros while they were en route to Novorossiysk. On December 10, a Sea Baby surface drone disabled the tanker Dashan. In each case, the vessels were reportedly forced to abandon their voyages, disrupting Russian oil export operations.
Russia responded with strikes on Ukrainian ports. On Friday, December 12, Geran-II drones and cruise missiles hit commercial shipping facilities in the Odesa region. At around 16:00 local time, the Turkish-owned car ferry Cenk T was struck while berthed at the port of Chornomorsk. The vessel was reportedly carrying food supplies. According to its owner, Cenk Denizcilik, two additional Turkey-linked cargo ships were damaged in subsequent strikes later the same day.
Retaliation or Pre-Emption?
Ukrainian officials have not explicitly stated whether the submarine strike was retaliation for the attacks on Odesa or a pre-emptive move. However, security analysts suggest it may have served both purposes.
Improved Kilo-class submarines are a key element of Russia’s ability to conduct long-range missile strikes and impose a potential naval blockade. While submarines are ill-suited for boarding or inspecting civilian vessels, they are highly effective tools for enforcing a “hard blockade” through the threat or use of missile and torpedo fire.
Despite suffering heavy losses during Ukraine’s 2022–2023 maritime campaign, Russia’s Black Sea Fleet remains, at least on paper, capable of interdicting civilian shipping to and from Odesa.
Novorossiysk’s Defenses Under Question
The reported success of the Sub Sea Baby drone raises serious questions about the effectiveness of Russia’s harbor defenses. Over the past two years, Novorossiysk has been outfitted with floating pontoons, booms, and other barriers intended to stop unmanned surface vehicles.
Those measures, however, were not designed to counter fully submerged threats. Until Russia deploys dedicated anti-UUV systems such as underwater sonar nets or patrols equipped with depth-charge-like countermeasures, the base may remain vulnerable to follow-up attacks.
If Novorossiysk can no longer be considered secure, Russia’s options are limited. Warships could be relocated further east to ports such as Sochi or Poti in Russian-occupied Abkhazia. However, those harbors lack the repair facilities, ammunition depots, and logistical infrastructure required to sustain high-tempo naval operations, potentially rendering much of the Black Sea Fleet combat ineffective.
Broader Strategic Implications
The strike also revives attention on other high-value Russian targets, most notably the Kerch Bridge linking Crimea to mainland Russia. The bridge has been attacked multiple times since 2022, including a June 3 operation involving underwater explosives equivalent to roughly 1,100 kilograms of TNT, which damaged its underwater supports and temporarily halted traffic.
Ukraine has repeatedly stated that destroying the Kerch Bridge is a strategic objective aimed at isolating Crimea and undermining Russia’s ability to sustain its forces on the peninsula. While existing defenses around the bridge are optimized against surface threats, the emergence of Ukrainian underwater drones introduces new uncertainties. Even so, experts caution that a single UUV may lack the explosive power required to collapse the bridge’s reinforced pillars.
Shrinking Russian Submarine Force
If the Novorossiysk submarine is indeed disabled, Russia’s operational submarine force in the Black Sea would be reduced to just two boats out of an original six. Two Improved Kilo-class submarines were deployed to the Mediterranean prior to the invasion and have remained there. A third, Rostov-on-Don, was destroyed on September 13, 2023, when Storm Shadow cruise missiles struck a dry dock in Sevastopol.
The Improved Kilo-class has been central to Russia’s naval power projection, not only in the Black Sea but also in the eastern Mediterranean. Continued losses would significantly constrain Moscow’s ability to threaten NATO’s southern flank and conduct long-range strike operations after the war in Ukraine.
As Ukraine continues to innovate in unmanned maritime warfare, the balance of power in the Black Sea appears to be shifting further away from Russia’s once-dominant fleet, with implications that may extend well beyond the current conflict.
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