The ship suffered a series of explosions and sank in unexplained circumstances between Spain and Algeria, according to multiple reports. The captain told Spanish investigators that the cargo consisted of parts for two reactors of the type used in military submarines, and he was unsure if they were loaded with nuclear fuel, according to Spanish government documents obtained by CNN and AP. A Russian Navy investigation concluded that the Ursa Major had been sunk as a consequence of an act of terrorism, according to Russian state media.
The Russian state-owned company Oboronlogistika claimed after the accident that the ship was subjected to a terrorist attack, according to Russian state media. The cause of the explosions remains unknown, and it is unclear whether the reactor components were loaded with nuclear fuel. The sinking may mark a rare and high-stakes intervention by a Western military to prevent Russia from sending nuclear technology to North Korea, according to CNN reporting.
A Spanish investigation, as described by a source, suggested the possible use of a rare type of torpedo to breach the ship's hull. US nuclear sniffer aircraft have flown over the sunken ship twice in the past year, according to public flight data. A suspected Russian spy ship visited the wreckage a week after it sank and set off four further explosions, a source familiar with the Spanish investigation said.
At the time of the sinking, the ship was en route from St. Petersburg to Vladivostok in the Russian Far East. The ship set sail two months after Kim Jong Un sent troops to assist with Moscow's invasion of Ukraine, according to multiple reports.
The incident occurred in the closing weeks of Joe Biden's presidency, when the war in Ukraine was peaking in Moscow's favor. The Ursa Major docked in Ust-Luga on December 2, then moved to St. Petersburg docks, and departed on December 11 bound for Vladivostok, according to its public manifest.
The manifest said it was carrying two large manhole covers, 129 empty shipping containers, and two large Liebherr cranes. In October 2024, Oboronlogistics stated that their ships had been licensed to carry nuclear material, according to a company statement. CNN analysis of time-lapse video footage showed containers being put inside the hull with a gap left below where the manhole covers would later sit.
Portuguese Navy aircraft and vessels tracked the ship through their waters, according to a Portuguese Navy statement. The Ursa Major was a heavy-lift ship built in Germany in 2009 as Scan Britania, and later renamed several times. At the time of sinking, the ship was owned by Russian state corporation Oboronlogistika.
The ship had two heavy cranes mounted on her port side, and her superstructure and bridge were on her forecastle. Its main engine was a single 8,000-kilowatt MAN B&W 16V32/40 diesel engine. The ship was registered in Novorossiysk by 2024, and its direct owner and operator was a company called SK-Yug.
In September 2019, as Sparta III, the ship brought cargo from China to Europe via the Northern Sea Route, saving €300,000, according to Oboronlogistika. In late 2020, Sparta III became ice-bound in the Yenisey river estuary.