A Russian cargo vessel believed to have been transporting components for two nuclear submarine reactors — possibly destined for — sank under mysterious circumstances in the Mediterranean Sea after a series of explosions near the coast of Spain, according to a CNN investigation.
The ship, the Ursa Major, went down on December 23, 2024, roughly 60 miles off Spain’s coast after what investigators described as multiple blasts near its engine room.
The new outlet reported that the vessel’s fate has remained shrouded in secrecy, with military activity around the wreckage adding to speculation surrounding the ship’s cargo and destination.
Ship reportedly carried submarine reactor components
According to the news outlet, the Spanish government later confirmed that the Russian captain told investigators the ship had been carrying “components for two nuclear reactors similar to those used in submarines.”
Spanish authorities as per the report said the captain was unable to confirm whether the reactor components contained nuclear fuel.
The incident occurred just months after .
Suspicious military activity after sinking
CNN reported citing publicly available flight data that US military “nuclear sniffer” aircraft flew over the wreck site twice after the sinking.
The wreckage was also allegedly visited by the Russian vessel Yantar, widely suspected by Western governments of espionage activities in NATO waters.
According to the news publication, four additional explosions were detected near the wreck after the Yantar arrived at the site.
Timeline of the sinking
The Ursa Major as per the news report departed from the Russian port of Ust-Luga on December 11, officially bound for Vladivostok in Russia’s Far East.
Its cargo manifest reportedly listed:
-Two large “manhole covers”
-129 empty shipping containers
-Two large Liebherr cranes
However, Spanish investigators later concluded the “manhole covers” were likely components of submarine nuclear reactors.
The vessel was escorted by Russian military ships including the Ivan Gren and the Aleksandr Otrakovsky while travelling through European waters.
Explosions near engine room killed crew members
According to CNN’s account of the Spanish investigation, the ship suddenly slowed on December 22 while passing through Spanish waters.
About 24 hours later, the Ursa Major reportedly issued a distress signal after suffering three explosions on its starboard side near the engine room.
The blasts killed two crew members and left the ship immobilised and listing heavily.
Fourteen surviving crew members evacuated aboard a lifeboat before being rescued by Spanish authorities.
Additional explosions reported before sinking
The news outlet said Spanish rescuers initially believed the vessel was stable and unlikely to sink immediately.
However, shortly after Russian naval vessel Ivan Gren ordered nearby ships to keep their distance, four more explosions reportedly occurred near the scene.
Spain’s National Seismic Network later reportedly confirmed that seismic signatures consistent with underwater blasts were detected at the exact time of the reported explosions.
The Ursa Major sank later that night.
Possible North Korea connection
According to CNN, the Spanish investigation examined the possibility that the cargo was ultimately intended for North Korea’s port of Rason.
Investigators reportedly questioned why Russia would transport seemingly ordinary cargo around the world by sea between two Russian ports instead of using the country’s extensive rail network.
The report suggested the onboard cranes may have been intended to assist with unloading sensitive cargo upon arrival in .
The report further stated that investigators believed the reactors may have been VM-4SG models commonly used in Russia’s Delta IV-class nuclear submarines.
“Targeted terrorist attack” claim
Four days after the sinking, the ship’s owner, Oboronlogistics, described the incident as a “targeted terrorist attack,” according to the outlet.
The company claimed investigators found a 50cm by 50cm hole in the ship’s hull and said metal fragments suggested an external strike.
Spanish lawmakers question official silence
Spanish lawmaker Juan Antonio Rojas Manrique questioned the lack of transparency surrounding the case.
Rojas also expressed doubts about official claims that recovering the ship’s black box from a depth of around 2,500 metres would be too difficult.
US nuclear surveillance flights deepen mystery
The news outlet reported that rare US Air Force WC-135R “Constant Phoenix” aircraft — commonly used to detect radioactive material and nuclear activity — conducted surveillance flights over the wreck area on August 28 and February 6.
The aircraft are typically deployed for monitoring nuclear activity in areas such as the Russian Arctic or around Iran.
There has been no public indication from Spanish authorities that radioactive contamination has been detected near the Mediterranean coast.
Investigation examines possible torpedo strike
According to CNN, Spanish investigators also examined whether the initial damage to the Ursa Major may have been caused by a supercavitating torpedo.
The investigation reportedly suggested the hole in the ship’s hull was consistent with a Barracuda-type high-speed torpedo capable of piercing hulls without a traditional explosive blast.
CNN said investigators believed such a weapon could explain the vessel’s sudden unexplained slowdown before the later explosions occurred.
Only a handful of countries — including the , , , and some NATO allies — are believed to possess such advanced torpedo systems.
