A Russian cargo ship, Ursa Major, which sank after a series of explosions in unexplained circumstances, may have been carrying two nuclear reactors bound for North Korea, according to a CNN report on Tuesday.
The circumstances surrounding the Ursa Major’s sinking have been shrouded in mystery since the incident occurred on December 23, 2024. Evidence from a Spanish-led investigation revealed the circumstances surrounding the sunken ship may point towards military intervention to prevent Russia from sending nuclear technology to North Korea.
Military activity around the wreckage site has heightened curiosity about its cargo and destination. United States nuclear “sniffer” aircraft have surveyed the site of the incident twice in the past year, according to publicly accessible flight data. The Ursa Major was part of Russia’s “Ghost Fleet” of vessels evading sanctions and was traveling from St. Petersburg to Vladivostok via the Mediterranean Sea, according to the ship’s public manifest.
The manifest also stated that the cargo on board consisted of only two large “manhole covers,” 129 empty shipping containers, and two Liebherr cranes. The ship was also escorted by two Russian Navy ships, the Ivan Gren and the Aleksandr Otrakovsky, according to a statement from the Spanish Government released earlier this year.
When the Ursa Major slowed dramatically, Spanish responders radioed to check if the vessel and crew were in distress. Twenty-four hours later, the ship veered sharply off its course and issued a call for help, according to the Spanish investigation. The crew reported the ship had sustained three explosions on its starboard side, near the ship’s engine room, killing two crew members and leaving the ship stranded at sea.
The 14 surviving crew members were rescued by Spanish authorities before one of the Russian military vessels escorting the Ursa Major ordered nearby ships to stay 2 nautical miles away from the incident site and demanded the immediate return of the crew. However, Spanish authorities insisted they needed to conduct rescue operations and begin investigating the explosion.
The Ursa Major was thought to be stable and recoverable, according to CNN. However, at 9:50 p.m., Ivan Gren (one of the Russian Military escorts of the Ursa Major) fired red flares over the scene, which were followed by four explosions detected by the Spanish National Seismic Network. By 11:10 p.m., the Ursa Major had sunk, according to the investigation.
Unusual circumstances surrounding the wreckage
The surviving Russian crew members were brought by Spanish authorities to the port city of Cartagena immediately following their rescue, where they were debriefed by police. According to the investigation, the crew and the ship’s captain were fearful of discussing the ship’s cargo and route.
Igor Vladimirovich Anisimov, the captain of the Ursa Major, reportedly came “under pressure to clarify what he meant by ‘manhole covers,’” found in the ship’s public manifest, the Spanish statement read.
“He finally confessed that they were the components of two nuclear reactors similar to those used by submarines. According to his testimony and without being able to confirm it, they did not contain nuclear fuel,” the statement added.
The Spanish investigation concluded that the items registered as “manhole covers” were likely nuclear reactor hulls used for nuclear propulsion, similar to those found in submarines.
The investigation reported that the ship’s captain, Anisimov, believed his route would be redirected to Rason, a North Korean port, to deliver the two reactor hulls.
A week after the incident, Russian military vessels returned to the scene of the wreckage for five days before four more explosions were recorded, potentially aimed to destroy the remains of the Ursa Major on the sea floor, a source close to the investigation told CNN.
CNN also reported on the US interest in the wreckage site. State-of-the-art US military aircraft known as “nuke sniffers” (usually based at Offutt Air Force Base in Nebraska) have been recorded surveying the wreckage scene twice over the last year, once on August 28, 2025, and again on February 6, 2026.
Kris Pierce, a spokesman for the base in Nebraska, told CNN the aircraft’s role “supports nuclear debris collection and analysis.”
“We cannot provide additional details regarding specific flight routing, mission findings, or any partner-related coordination,” Pierce added.
Another “nuke-sniffer” took a similar flight path a year before the Ursa Major sank, suggesting the surveys conducted by the US military may be routine, according to analysts at CNN.
Sources close to the investigation told CNN that the Ursa Major’s captain, Anisimov, told Spanish authorities he did not recall hearing an explosion on December 22 when the ship abruptly slowed. The following day, three explosions near the engine room killed two crew members whose bodies were not recovered.
The Spanish investigations suggested the explosion was potentially made by a Barracuda supercavitating torpedo, a high-speed torpedo that only the US, Russia, Iran, and a few NATO member states are believed to possess.
