Russian Submarine Novorossiysk Suffers Fuel Leak, Returns to Port for Repairs

Mechanical Failure Forces Russian Submarine to Surface

The Russian diesel-electric submarine Novorossiysk (B-261), a Project 636.3 'Improved Kilo' class vessel armed with Kalibr cruise missiles, suffered a significant mechanical failure in late September 2025. The incident, which occurred while the submarine was on deployment in the Mediterranean Sea, involved a severe fuel system leak that caused diesel fuel to flood part of its hull. This malfunction forced the submarine to surface and commence a prolonged return journey to its home port for urgent repairs.

Details of the Malfunction and Explosion Risk

Reports indicate that the malfunction, which surfaced around September 26-27, 2025, led to diesel fuel leaking directly into the submarine's bilge compartment. This accumulation of fuel created a 'highly volatile' situation and posed a significant 'explosion risk' onboard the vessel. Sources, including the Russian Telegram channel VChk-OGPU, suggested that the crew lacked the necessary spare parts and qualified specialists to address the leak at sea. There were even considerations by the crew to pump the fuel directly into the sea as an emergency measure to prevent a catastrophic explosion, raising concerns about potential environmental impact. The severity of the situation drew comparisons to the 2000 Kursk disaster, highlighting the inherent dangers of technical failures in undersea warfare assets.

Long Journey Home Under Surveillance

The Novorossiysk had been operating in the Mediterranean since June 2025. Due to Turkey's closure of the Bosphorus Strait to warships under the Montreux Convention, invoked following Russia's full-scale invasion of Ukraine, the submarine was compelled to take a significantly longer route from the Baltic Sea to reach the Mediterranean. The mechanical failure necessitated its return to Saint Petersburg for repairs, a journey of thousands of kilometers. The submarine's return voyage was conducted in surface mode, making it vulnerable and visible. It was reportedly tracked and escorted by naval and air forces from several NATO countries, including France, Sweden, the Netherlands, and the United Kingdom, as it passed through international waters. This incident underscores broader challenges facing Russia's naval operations, particularly the diminished ability to sustain missions in the Mediterranean following the reported loss of its naval logistics hub at Tartus, Syria, in 2024.

Submarine Profile and Official Response

The Novorossiysk, commissioned in 2014, is a Project 636.3 Varshavyanka-class submarine, known for its stealth capabilities and armament of Kalibr-PL cruise missiles. These missiles are capable of striking both sea and land targets at considerable distances. The submarine typically carries a crew of approximately 52 sailors and has a submerged displacement of over 3,900 tons. Despite widespread reports of a serious malfunction, the Russian Black Sea Fleet issued a statement denying any technical failure. They asserted that the Novorossiysk was conducting a 'routine inter-fleet transfer' after completing missions in the Mediterranean, and that surfacing in the English Channel is a standard procedure according to international navigation rules.