Russian Ursa Major Sinks Off Spain After Explosions Carrying Submarine Nuclear Reactor Components

A Russian cargo ship, the Ursa Major (also known as Sparta 3), sank in the Mediterranean Sea about 60 miles off the coast of Spain after suffering multiple explosions, with CNN reporting it may have been carrying “components for two nuclear reactors similar to those used in submarines.”

CNN said the ship issued an urgent call for help at 11:53 a.m. UTC on December 23, after three explosions on its starboard side likely near its engine room killed two crew members, leaving the vessel listing and immobile.

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The Guardian reported the Ursa Major put out a distress call at 12.53pm and that by 11.20pm it had sunk and now lies at a depth of 2,500 metres, with 14 crew members rescued.

Spanish attempts to assist were curtailed when a Russian warship arrived and ordered the two Sasemar boats to withdraw to a distance of two nautical miles, and the Russian warship then launched flares over the Ursa Major, according to a Spanish government document cited by The Guardian.

CNN added that the wreckage was later visited by a suspected Russian spy ship that set off four further explosions, deepening the mystery around what the ship was carrying and how it sank.

CNN reported that the Spanish government released a statement on February 23 after pressure from opposition lawmakers, confirming that the ship’s Russian captain told investigators the Ursa Major was carrying reactor components and that he was unsure if they were loaded with nuclear fuel.

In that same CNN account, the Spanish investigation described by a source familiar with its contents suggested the incident “may have involved the use of a rare type of torpedo to breach the ship’s hull.”

CNN

The Guardian, meanwhile, said the captain eventually told Spanish investigators that the “manhole covers” onboard were “nuclear reactor components similar to those used by submarines,” but that no nuclear fuel was being transported.

The Guardian also reported that a CNN investigation noted “four similar seismic signatures … the pattern of which resembled underwater mines or overground quarry blasts” heard just after flares were fired.

Separately, the New York Post described a prevailing theory that the West might have been involved, saying the Ursa Major suffered multiple explosions while allegedly carrying two nuclear reactors believed to be bound for North Korea.

The Guardian reported that the Ursa Major was officially transporting “non-dangerous merchandise” including 129 shipping containers, two cranes, and two large maintenance hole covers, while its route and sinking raised suspicions for Spanish authorities.

CNN said US nuclear “sniffer” aircraft have flown over the sunken ship twice in the past year, and it described the wreckage as being visited a week after it sank by a suspected Russian spy ship that set off four further explosions.

The New York Post said Spain told lawmakers it was far too risky to investigate the wreckage sitting at 8,202 feet below the water “without significant technical resources,” and it also reported that the US deployed its WC135-R “nuke sniffer” aircraft twice, once on Aug. 28, 2025 and again on Feb. 6 of this year.

The Guardian reported that by 11.20pm the Ursa Major had sunk and that two crew members are thought to have died in the initial explosions, while 14 were rescued, leaving the incident’s human toll and technical cause intertwined with the competing narratives.

With the ship’s alleged reactor components linked to North Korea, CNN framed the episode as potentially preventing “an upgrade in nuclear technology to a key ally, North Korea,” while the New York Post said the owner Oboronlogistics claimed the vessel was struck in a “targeted terrorist attack.”