A Russian cargo vessel, allegedly transporting two nuclear reactors intended for submarines to North Korea, faced a series of explosions and sank on December 23, 2024, approximately 60 miles off the Spanish coast.
On Tuesday, a CNN investigation suggested that the sinking might have been the result of a Western military intervention aimed at halting a significant transfer of nuclear technology.
The vessel, MV Ursa Major, also known as Sparta 3, was owned by the Russian state company Oboronlogistics, connected to the Ministry of Defense. In October 2024, the company declared it had a license to transport nuclear materials.
The official manifest listed Vladivostok as its destination and included cargo described as two large "hatch covers," 129 empty containers, and two Liebherr cranes.
Under the scrutiny of Spanish investigators, Russian captain Igor Anisimov eventually admitted that the cargo was composed of components for two nuclear reactors similar to those used in submarines. However, he could not confirm if they contained nuclear fuel, according to a statement from the Spanish government to lawmakers in February 2026.
The Spanish investigation concluded that the likely real destination was North Korea's port of Rason. It highlighted the improbability of a lengthy maritime journey to deliver such cargo between two Russian ports when an extensive railway network connects them.
Uncovering the Real Destination
The reactors were believed to be VM-4SG models, typically installed on Russia's Delta IV-class ballistic missile submarines.
On December 22, the ship inexplicably slowed down in Spanish waters, and 24 hours later, it experienced three explosions on its starboard side, which resulted in the deaths of two crew members, second mechanic Nikitin and mechanic Yakovlev. Their bodies were never recovered.
The 14 survivors were rescued by the Spanish vessel Salvamar Draco and brought to the port of Cartagena.
The Final Moments and Subsequent Explosions
As the Ursa Major appeared stable, the Russian escort ship Ivan Gren launched red flares over the scene, followed by four additional explosions recorded by the Spanish National Seismic Network, causing the ship to sink at 23:10 UTC.
A week later, the Russian spy ship Yantar, accused of espionage in NATO waters, lingered over the wreckage for five days, during which four more explosions were detected, possibly aimed at destroying evidence on the seabed.
Speculations and International Implications
Spanish investigators suggested that a 50-by-50-centimeter hole found in the hull, with the metal bent inward, might have been caused by a supercavitating Barracuda torpedo, a weapon only possessed by the US, certain NATO allies, Russia, and Iran.
Defense intelligence analyst Mike Plunkett from Janes offered another theory: "It sounds like a shaped explosive charge placed against the hull by someone or something."
The sinking occurred just two months after Kim Jong Un dispatched at least 10,000 North Korean soldiers to support Russia in the Kursk region, following the Comprehensive Strategic Partnership Treaty signed by Putin and Kim on June 18, 2024, which includes a mutual defense clause akin to NATO's Article 5.
Pyongyang has openly demanded that Moscow share its nuclear technical expertise, with these demands intensifying after the troop deployment.
North Korea's Nuclear Ambitions
On December 25, 2025, Kim Jong Un inspected the construction of what North Korea claims is its first 8,700-ton strategic nuclear submarine, though images show only a sealed hull without evidence of a functional reactor, supporting the theory that Pyongyang needed the Russian reactors to complete the project.
Plunkett cautioned that any Russian decision to transfer this technology "is not taken lightly and is something only done between very close allies," calling the potential development "highly concerning, especially if you're South Korea."
The remains of the Ursa Major lie at a depth of about 2,500 meters, and Spanish legislator Juan Antonio Rojas Manrique, a former merchant marine captain, expressed his skepticism: "Nowadays, black boxes usually float to the surface with a locator. I believe someone has the black box. But we don't know if it's Spain or if the Russians themselves have found it."
Key Questions About the Russian Ship Sinking
What caused the sinking of the Russian cargo ship?
The sinking might have been triggered by a Western military intervention to prevent a major transfer of nuclear technology, although there are various theories, including an internal explosion or an attack by a supercavitating torpedo.
What was the cargo ship carrying?
The ship was reportedly carrying components for two nuclear reactors similar to those used in submarines, along with other declared items such as large hatch covers, empty containers, and cranes.
Why is the potential transfer of nuclear reactors to North Korea concerning?
The transfer of nuclear reactors to North Korea is alarming due to the potential escalation of nuclear capabilities in the region, especially given North Korea's strained relations with South Korea and other nations.