A ticking 'mercury bomb'? Ancient Nazi U-boat lies off Norway

In the depths of the ocean, roughly 150 metres beneath the surface off the Norwegian island of Fedje, the remnants of an ancient Nazi U-boat have been discovered. The submarine, designated U-864, has been resting there for over eight decades, its presence accompanied by a cargo that still poses an environmental concern. Historical records reveal that the vessel was reportedly loaded with a significant amount of mercury, estimated to be between 65 and 67 tonnes, although the exact quantity remains undetermined due to the loss of loading documents.

The U-864's final voyage, set for February 1945, was a mission of great consequence. The German submarine was tasked with delivering military and technical equipment to Japan, a journey that took it through Norwegian waters. However, the mission was cut short when the British submarine HMS Venturer intercepted U-864. On February 9th, 1945, Venturer's torpedo struck the German sub, causing it to sink to a depth of around 150 metres.

All 73 crew members perished in the attack, which is recognized as the sole known instance where a submerged submarine sank another.

Decades passed before the U-864 was found again. In 2003, the Norwegian naval vessel KNM Tyr located the wreck, which was found to be broken into two parts at a depth of approximately 150 metres. The cargo onboard, particularly the mercury, posed a significant environmental threat, as mercury does not dissipate easily. It can remain in the ecosystem for years, even centuries, and can be converted into methylmercury – a highly toxic form that accumulates in the food chain, particularly in fish.

Recent examinations of the wreck using remotely operated underwater vehicles have provided new insights into its current state. Many of the presumed 1,867 containers are likely damaged, having been crushed during the sinking. In 2026, the Norwegian Coastal Administration conducted operations to recover some of the mercury-laden containers.

However, the recovery process itself led to the release of around 0.5 tonnes of mercury into the water, an outcome that mirrors the ongoing dilemma faced by authorities. Should they attempt to remove the dangerous cargo, or instead seal the wreck and its contaminated seabed for good? The choice presents a complex challenge, as large-scale recovery could potentially release more pollutants than it would retrieve, while permanent sealing also presents its own set of long-term management requirements.

The discovery of the U-864 has prompted ongoing research into the local marine life, with tests indicating stable or low mercury levels in fish and shellfish. Nevertheless, the question of how to manage the wreck remains unresolved, leaving the people of Fedje and the Norwegian authorities to grapple with the legacy of this historical relic.