The sinking of the Russian cargo ship Ursa Major has evolved from a maritime accident into a politically charged dispute involving nuclear technology, sanctions, and alleged covert transfers. 

The vessel, owned by Oboronlogistika, a Russian Defense Ministry–affiliated logistics firm under U.S. sanctions, went down in international waters of the Mediterranean Sea between Spain and Algeria on December 23–24, 2024 after multiple explosions caused severe listing and flooding. 

Spanish authorities rescued 14 crew members, while two remain missing.

Russian officials initially attributed the incident to an engine room explosion. 

Within days, that explanation shifted. Moscow and the ship’s owner described the sinking as a “terrorist act,” claiming three explosions struck the starboard side of the hull. They pointed to a hole bent inward as evidence of an external impact. No independent investigation results were released at the time, and the official account relied solely on Russian statements.

According to Russian disclosures in December 2024, the Ursa Major was carrying empty containers, two large port cranes, and two 45-ton hatch covers intended for the nuclear-powered icebreaker Rossiya, part of the Project 10510 Lider class, with Vladivostok listed as the destination. 

Pre-sinking photographs, however, showed two large objects on the stern deck covered with blue tarps, drawing scrutiny from maritime analysts.

These items were officially described as icebreaker hatch covers. Yet their size, shape, and deck placement prompted questions in specialist media even before the ship sank. At the time, no alternative cargo explanation was formally advanced by Western governments or international bodies.

A year later, new claims surfaced. On December 28–29, 2025, Spanish newspaper La Verdad reported that Spanish authorities had concluded the tarped cargo was not icebreaker equipment. 

Instead, investigators allegedly assessed the objects as unfueled casings for two VM-4SG naval nuclear reactors, a Soviet-era design historically used in submarines. 

La Verdad cited aerial imagery said to show coolant and steam piping, along with lead shielding consistent with reactor components rather than hatch covers.

Investigators reportedly suspect the intended destination was a North Korean port, possibly Rason, implying assistance to Pyongyang’s nuclear-powered submarine ambitions and a potential violation of international sanctions. No public evidence has emerged confirming nuclear fuel was aboard; the components were described as unfueled casings.

Additional claims surround events during and after the rescue. Spanish reporting alleged that a Russian naval vessel, Ivan Gren, interfered with rescue operations, demanded control of the scene, and fired flares, possibly to obscure satellite observation. In January 2025, the Russian “oceanographic research” ship Yantar, widely regarded in Western naval analysis as a dual-use intelligence platform equipped with deep-sea submersibles, arrived at the wreck site at approximately 2,500 meters depth. Its presence fueled speculation about efforts to inspect, recover, or destroy sensitive cargo.