Russian submarine Novorossiysk surfaces near Gibraltar after fuel leak sparks explosion risk.

A Russian Kilo-class submarine, the B-261 Novorossiysk, was forced to surface near the Strait of Gibraltar in late September after a fuel-system failure created an explosion risk.

A Russian Improved Kilo-class submarine of the Black Sea Fleet, the Novorossiysk (B-261), experienced a major technical failure while on duty in the Mediterranean in late September 2025. On September 27, 2025, the Telegram channel VChK-OGPU leaked documents reporting that damage to the fuel system created an explosion risk and forced the submarine to surface near the Strait of Gibraltar, while GBC (Gibraltar Broadcasting Corporation), the public service broadcaster for Gibraltar, said questions had been put to the UK Ministry of Defence and that local authorities regarded the matter as one for the MoD.
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The Novorossiysk, commissioned in 2014, is the lead unit of the Project 636.3 class, also referred to as Improved Kilo II, and carries six 533 mm torpedo tubes that can launch torpedoes, naval mines, or Kalibr cruise missiles. (Picture source: X/Peter Ferrary)

According to VChK-OGPU, the Novorossiysk’s fuel system was so severely damaged that fuel was leaking directly into the bilges, creating a highly explosive situation that the crew was not equipped to fix at sea. The leaked report stated that no repair parts or qualified specialists were available on board, leaving the personnel unable to carry out technical corrections as the problems multiplied across other systems. Faced with rising danger, the crew began pumping the accumulated fuel directly into the sea in an emergency procedure to reduce the immediate risk of detonation. The submarine, which had been on duty in the Mediterranean, was forced to remain surfaced near the Strait of Gibraltar, a narrow and heavily trafficked passage, as the crisis developed. GBC added that British press reports said that the incident led to a major alert being declared in the Mediterranean Sea.

UK coverage noted that the British Royal Navy shepherded the Novorossiysk out of the English Channel in January 2025 as it headed for the North Sea, and recent reporting tracked the Russian tug Jakob Grebelsky working with the submarine in the Mediterranean, then moving west off Portugal after the malfunction. The same set of reports recorded allied surface ships, multiple NATO aircraft, and a P-8 maritime patrol plane monitoring near Portugal, while some claims pointed to weather conditions playing a role in the submarine’s difficulties. At the same time, the UK press raised the fear that an explosion could have occurred had the submarine suffered its fuel leak while transiting the Channel, underlining the risks associated with a surfaced submarine with a fuel-system failure in a narrow sea lane.

The B-261 Novorossiysk is the lead unit of Project 636.3, also referred to as the Improved Kilo II class, which is an upgraded development of the original Soviet Project 877 Kilo-class design created by the Rubin Design Bureau in the 1970s. The submarine was laid down at Admiralty Shipyards in Saint Petersburg on 20 August 2010, launched on 28 November 2013, and commissioned into the Russian Navy on 22 August 2014 as part of the Black Sea Fleet’s 4th Independent Submarine Brigade. In terms of design, the boat is 74 metres long, with a beam of 9.9 metres and a draft of 6.1 metres, and has a surfaced displacement of about 2,350 tons and a submerged displacement of approximately 3,100 tons. It is propelled by a diesel-electric system consisting of two 1,000 kW diesel generators and a main electric motor driving a single shaft, supported by auxiliary motors, which provide speeds of 11 to 17 knots on the surface and up to 20 knots submerged. Endurance is rated at 45 days, with a test depth of 300 metres and an operational depth around 240 metres. The standard crew is 52 sailors, including 12 officers, who operate the submarine’s navigation, propulsion, and combat systems.

Its weapons suite is centered around six bow-mounted 533 mm torpedo tubes that can be reloaded automatically, giving the submarine a load of 18 torpedoes or 24 mines depending on configuration. In addition, it can carry up to four Kalibr cruise missiles, including anti-ship, land-attack, and anti-submarine variants, launched through the torpedo tubes. For air defense, portable systems such as the Strela-3M, Igla-1, or Verba can be embarked, with up to eight missiles available for close-range protection. The submarine’s hull is covered with anechoic tiles that absorb active sonar signals and reduce its acoustic signature, an important feature in the confined waters of the Black Sea and Mediterranean. These design elements, combined with modernized sonar and fire-control systems, make the Project 636.3 series the most advanced of the Kilo lineage, which has been exported to several countries, including Algeria, Vietnam, and China.

The Novorossiysk’s role within the Russian Navy has included sea-denial missions, coastal defense, and strike operations, and it has previously launched Kalibr missiles during deployments in support of Russian operations in Syria. The unit’s record includes multiple Mediterranean deployments and a refit that began in February 2021, followed by a reported return to service planned for April 2024. It deployed again to Tartus in September 2024, participated in a Mediterranean exercise in December 2024, and left the region in early January 2025 rather than returning to the Syrian base. Earlier, during its 2015 transfer to the Black Sea, it stopped in the Spanish port of Ceuta, which prompted UK attention because of proximity to Gibraltar, and it has since been associated with Kalibr-capable operations in the region; within the class, Rostov-on-Don was later reported as severely damaged and then claimed destroyed in 2024, underscoring the operational value attributed to these submarines.

Since the start of the war with Ukraine in 2022, the Russian Navy has faced repeated difficulties in maintaining and repairing its vessels. On 7 August 2025, the small missile ship Vyshniy Volochek of the 41st Missile Boat Brigade collided with a civilian tanker in Temryuk Bay while carrying out naval tasks. The impact caused visible structural damage to the hull, though the incident was later described officially as having occurred during a drone attack and said not to affect combat readiness. Around the same time, another ship of the same class was struck by a Ukrainian drone in the Azov Sea, showing that both accidents and enemy action were taking a toll. Beyond combat losses, vessels of the Black Sea Fleet have returned to port with temporary repairs that were easily visible, sometimes patched with canvas or metal plates. Others have been unable to operate independently, remaining inactive at piers or being moved from place to place by tugboats. In parallel, the tug Kapitan Ushakov, still undergoing outfitting at the Baltic Shipyard, capsized and sank at its mooring before it could be delivered, further reducing the auxiliary support available to the fleet.

Russian naval sustainment has also been affected by technical and industrial constraints. After 2022, sanctions made it impossible to continue using Western-made components in submarines and surface combatants, and approximately 90 percent of those parts were replaced with domestic or Chinese substitutes. This substitution did not always match the quality of the original components, and reliability issues became more frequent. At the same time, the cost of repairs remained high and maintenance times lengthened, with some submarines spending months inactive before returning to service. For instance, the May arrest of a ship-repair plant head in a case valued at roughly 4 million rubles, continued mechanical issues on the legacy submarine Alrosa, now described as physically and technically worn out, suffering persistent mechanical problems, but kept in service because of the shortage of modern boats.

Structural constraints were also linked to lost or limited repair infrastructure. These include the earlier loss of the PD-50 floating dock, the strike on an MPSV07 ship, and the prolonged Admiral Nakhimov and Pyotr Velikiy overhaul, plus efforts to disperse work and explore a support site at Ochamchire that would not quickly replicate Crimean depth in cranes, workshops, and test ranges. In combination, the sustainment picture is described as longer downtime per hull, more dispersal to secondary ports, and a Black Sea repair ecosystem that remains fragile and capacity-constrained, which sets the backdrop for how quickly an at-sea fuel-system failure on Novorossiysk could be remediated.

Written by Jérôme Brahy

Jérôme Brahy is a defense analyst and documentalist at Army Recognition. He specializes in naval modernization, aviation, drones, armored vehicles, and artillery, with a focus on strategic developments in the United States, China, Ukraine, Russia, Türkiye, and Belgium. His analyses go beyond the facts, providing context, identifying key actors, and explaining why defense news matters on a global scale.