Originally published by James Marinero on Medium
What happened
The Russian cargo vessel Ursa Major sank in the Mediterranean Sea on 23 December 2024 following a series of events that remain a subject of intense international scrutiny.
While transit was officially recorded as a voyage from Saint Petersburg to Vladivostok, the ship exhibited erratic movements off the coast of Almeria (Spain) on 21 December. By the following day, the vessel had significantly reduced speed and began to drift. A distress signal was eventually transmitted on 23 December from a position approximately 60 nautical miles south of Cartagena.
Spanish rescue services successfully evacuated 14 of the 16 crew members, though two engineers remained missing. Observations made during the rescue indicated that the engine room door was locked from the outside and the vessel was listing heavily.
Although the official Russian narrative attributed the sinking to internal explosions caused by a terrorist act, Spanish investigators later identified hull damage consistent with an external strike.
Physical evidence suggests a hole with inward-facing edges was created by a supercavitating torpedo, likely deployed to prevent the delivery of sensitive cargo.
The detailed report was published by La Verdad in Spain.
Russian recovery attempt
In the immediate aftermath of the sinking, the Russian military took unconventional steps to secure the site. The landing ship Ivan Gren arrived at the scene and reportedly attempted to interfere with Spanish rescue and monitoring efforts. This vessel fired red signal flares into the air, an action believed to be intended to obstruct the infrared sensors of reconnaissance satellites overhead.
The Russian commander also demanded that Spanish patrol vessels withdraw from the area despite the incident occurring in international waters.
Following the sinking of the vessel to a depth of 2,500 metres, the Russian oceanographic research ship Yantar was dispatched to the wreckage site in January 2025.
This ship Yantar, which I have written about several times, is equipped with deep-sea submersibles capable of reaching depths of 6,000 metres, spent several days operating over the wreck. It is believed that this mission was designed to either recover or destroy sensitive components of the cargo to prevent them from being inspected by Western authorities.
The Ursa Major
The Ursa Major was a heavy-lift cargo ship with a length of 142.47 metres and a beam of 23.20 metres. Built in 2009 at the Peene-Werft shipyard in Germany, the ship possessed a deadweight of 9,490 tonnes and a maximum speed of 17 knots. It was powered by a single 8,000-kilowatt MAN B&W diesel engine and was classified with an ice class of 1A, allowing it to navigate through moderate ice conditions.
The ship was operated by Oboronlogistika, a company closely associated with the Russian Ministry of Defence and subject to international sanctions. For several years, the vessel was a primary component of the so-called Syrian Express, transporting military equipment and ammunition to the Russian naval base at Tartus.
At the time of its loss, the ship was equipped with two large cranes on its port side, which were reportedly intended for port development in the Russian Far East but are suitable for unloading heavy cargo.
Latest developments
Recent reports from the Spanish publication La Verdad have provided further insight into the nature of the cargo. Although the manifest listed empty containers and hatch covers for icebreakers, investigators concluded that the ship was actually transporting two VM-4SG nuclear reactor casings.
Vessel Tracker updates confirm that Spanish investigators used aerial images — often collected by patrol aircraft — to identify the two large, undeclared containers on the ship’s stern as VM-4SG reactor housings. These are not visible in the publicly available pictures.
These components are typically used in the propulsion systems of Russian nuclear submarines.
The Spanish investigation suggests that the final destination for these reactors was not Vladivostok, but rather the North Korean port of Rason. This assessment is based on the presence of specialised cranes on the deck, which would have been necessary to unload heavy reactor components in a port with limited infrastructure.
It is now suspected that the sinking was a deliberate intervention by Western forces to halt the clandestine transfer of nuclear technology to North Korea.
Strategic concealment and deniability
By using a vessel from the ‘shadow fleet’, such as the Ursa Major, the Russian state was able to obscure the nature of the cargo within a standard maritime manifest.
The sea route allowed the reactor components to be hidden amongst legitimate industrial equipment, including large Liebherr cranes and icebreaker hatch covers. This provided a layer of ‘plausible deniability’ that rail transport could not offer.
The choice of the Mediterranean route, although significantly longer than the Northern Sea Route in the Arctic, was also a tactical decision. By sailing through international waters the vessel could maintain a profile that appeared to be a routine commercial delivery.
Additionally, the inclusion of heavy-duty cranes on the ship’s deck ensured that the reactors could be unloaded at the destination port of Rason without the need for sophisticated local infrastructure, which would have been another point of detection if prepared in advance on land.
The torpedo
The sinking of the Ursa Major has been attributed by Spanish investigators to a strike from a supercavitating torpedo, a weapon system possessed only by Russia, China, and some NATO members.
Unlike conventional torpedoes, which are limited by water resistance, these weapons generate a gas bubble around their hull to reduce drag, allowing for speeds exceeding 200 knots.
These torpedoes have a distinctive nose to create the bubble and often use rocket propulsion to maintain high speeds. The technology is complex.
Russia’s VA-111 Shkval, in service since 1977, is a prime example, reaching speeds up to 290 mph. and a range of 10 miles. Iran’s Hoot, believed to be reverse-engineered from the VA-111, can reach 220 mph but has a limited range of six miles. The USA has not publicly declared a Mark number for such a torpedo.
Analysis of the Ursa Major wreckage revealed a distinct 50-centimetre breach with inward-deformed plating, a characteristic of high-kinetic external impact rather than an internal explosion.
The investigation by La Verdad suggests that a Western submarine was responsible for the interception.
While several nations possess the technical capacity to deploy such advanced underwater projectiles, the geopolitical context points toward a joint initiative between the United States and South Korea.
These nations had the greatest strategic interest in preventing the clandestine transfer of nuclear submarine technology to North Korea. By utilising a high-speed, non-explosive or low-yield variant of the torpedo, the attacking party successfully disabled the vessel while minimising the risk of a broader environmental catastrophe in the Mediterranean.
A report suggests that a US Navy P-8A Poseidon aircraft that was reportedly monitoring the vessel prior to the strike.
Implications and conclusions
The sinking of the Ursa Major highlights the fragility of clandestine military-technical cooperation between Moscow and Pyongyang.
This incident demonstrates that even the “shadow fleet” remains vulnerable to sophisticated maritime interventions when transporting strategic assets.
Intelligence indicates that the VM-4SG reactor casings were monitored from their point of origin at the Sevmash shipyard in Severodvinsk. Western surveillance tracked the components as they were integrated into the vessel’s manifest under the guise of civil icebreaker equipment.
The conclusion of the Spanish maritime authorities suggests a significant escalation in international efforts to enforce nuclear non-proliferation.
By successfully intercepting the shipment, Western forces have effectively delayed North Korea’s ambitions to develop a functional nuclear-powered submarine fleet. Such a fleet would be capable of reaching the home waters of the USA.
The loss of these specific reactor casings, which were likely salvaged from Russian decommissioned Delta IV-class submarines, represents a non-renewable setback for the North Korean nuclear submarine program.
While the Russian rail system is huge, it cannot sustain the clandestine transfer of sensitive military technology without detection.
And they are not much better with the sea route either.
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