The Ursa Major is seen in a photo taken by the Portuguese Air Force as the Russian vessel sailed through Portuguese waters in December 2024. Courtesy: Portuguese Air Force
A Russian cargo ship that sank in the Mediterranean under mysterious circumstances may have been transporting submarine nuclear reactor components to North Korea, raising serious questions about covert military cooperation between Moscow and Pyongyang.
The vessel, the Ursa Major, went down off the coast of Spain in December 2024 after a series of explosions ripped through its hull. Spanish investigators later stated that the ship’s captain told authorities the cargo included components for two submarine-style nuclear reactors, though he reportedly could not confirm whether nuclear fuel was onboard. The case has since drawn international attention because of unusual military activity around the wreck and growing concerns over Russia’s ties with North Korea, as reported by CNN
The Ursa Major had departed from Russia’s Baltic region with a public manifest listing ordinary industrial cargo, including cranes and container equipment. Investigators later became suspicious about the declared cargo after reviewing loading footage and testimony from crew members. Spanish authorities say the captain eventually admitted that the large “manhole cover” items listed in shipping records were actually reactor-related components similar to those used in submarines.
The ship had been escorted by Russian military vessels during part of its journey through European waters. According to the investigation, the vessel first slowed unexpectedly on December 22 before suffering three explosions near its engine room roughly 24 hours later. Two crew members were killed, and the remaining sailors abandoned ship before rescue teams arrived.
What happened next added another layer of intrigue. Spanish rescue crews reported that the ship initially appeared stable and unlikely to sink quickly. However, shortly after a Russian military vessel ordered nearby ships to keep their distance, several more explosions were reportedly detected. Seismic monitoring systems later recorded signatures consistent with underwater blasts in the same area.
Investigators are still debating what caused the initial damage. One theory mentioned in the Spanish investigation involves a high-speed supercavitating torpedo capable of punching through a ship’s hull without a large explosion. Other defense analysts believe a limpet mine or shaped-charge explosive is a more plausible explanation.
The wreck itself has since become the focus of international interest. A suspected Russian spy ship later spent days above the wreck site, while specialized US aircraft designed to detect radioactive material reportedly flew over the area on multiple occasions.
The incident has also fueled speculation about possible Russian transfers of sensitive nuclear technology to North Korea. The timing is notable, coming after Pyongyang publicly showcased what it claimed was its first nuclear-powered submarine and after North Korean troops reportedly assisted Russia during the war in Ukraine.
Neither Russia nor Spain has publicly released full details of the investigation. For now, many of the answers remain buried roughly 2,500 meters below the Mediterranean Sea.