What Salvage Divers Found Inside Sunken Nazi Germany Submarine Will Leave You Speechless

The $67$-Ton Time Bomb: The Terrifying Secrets and Ecological Crisis of Nazi Submarine U-864

In the cold, dark waters off the coast of Norway, an international crisis lay dormant for six decades. The ghost story of a vanished Nazi submarine, its mission, and its secrets were finally laid bare in 2003 when the Royal Norwegian Navy made a stunning discovery: the mangled wreck of U-864, lying broken in two on the seabed, 150 meters below the surface.

This was no ordinary wreck. The U-864 was carrying a cargo so dangerous its discovery triggered a decades-long environmental dilemma: nearly 67 tons of metallic mercury and the technological crown jewels of the Third Reich, secrets that could have prolonged World War II and changed the trajectory of the Pacific conflict.

Operation Caesar: The Floating Lifeline

In late 1944, as the Allies closed in, Nazi Germany launched one of its last desperate gambits: Operation Caesar. The goal was to bolster Japan’s crumbling war effort with critical technology and scarce raw materials.

The vessel chosen was the U-864, a formidable Type IXD/2 cruiser U-boat built for extreme endurance. It was converted from a hunter into an underwater courier for a mission that would take it the length of the globe. Command fell to Corvette Captain Ralf Reuther, charged with ferrying:

67 Tons of Metallic Mercury: Packed in 1,857 steel flasks, this mercury was essential for Japanese munitions factories to produce mercury fulminate for primers and detonators.

Jumo 004 Jet Engine Components: The plans and key parts for the engine that powered the revolutionary Messerschmitt Me 262, the world’s first operational jet fighter.

V-2 Ballistic Missile Components: Critical guidance systems and blueprints for the world’s first long-range guided ballistic missile.

Human Cargo: Two Messerschmitt jet engineers and two Japanese specialists carrying invaluable technical expertise.

The cargo turned the submarine from a weapon into a floating lifeline for a desperate ally.

The Duel of the Submerged Ghosts

The voyage was cut brutally short. Allied intelligence, aided by British codebreaking, put HMS Venturer, a V-class submarine under Lieutenant James S. Launders, on the scent off Fedje, Norway.

On February 9, 1945, the two submarines engaged in a unique duel, submerged and relying solely on sound. Launders ordered a spread of four torpedoes. U-864 evaded the first three, but tragedy—or strategic geometry—led it directly into the path of the fourth. The impact split the U-boat and sent her to the seabed, killing all 73 souls aboard.

The sinking remains the only documented instance in history in which one submerged submarine sank another while both were submerged.

The Technological Crown Jewels

The cargo of U-864 represented the pinnacle of Nazi engineering, intended to give Japan the ability to strike back at the American B-29 Superfortresses and naval fleets.

Jumo 004 Jet Secrets

The Jumo 004 was a masterpiece of engineering, utilizing an axial flow compressor—the same basic principle used in most commercial and military jet engines today. Had the components and blueprints arrived in Japan, they could have:

Skipped Years of R&D: Japanese engineers could have bypassed trial-and-error to mass-produce advanced jet engines.

Transferred Know-How: Onboard were Messerschmitt engineers Ralf von Klinganberg and Ricklef Schmerus, the architects who held the non-blueprint knowledge—the solutions to production problems and the nuance of making the complex machine work. Their loss was an intellectual blow as significant as the loss of the physical parts.

V-2 Missile Components

U-864 also carried components and technical drawings for the V-2 ballistic missile, the most advanced weapon in the world, capable of arcing high into the atmosphere and descending on a target without warning.

The Blueprint Advantage: The cargo included critical guidance systems and manufacturing plans. This knowledge would have allowed Japanese scientists to potentially reverse-engineer the entire weapon, including the rocket motor and complex guidance mechanics.

Changed the Naval War: A Japanese V-2 variant could have created long-range strategic weapons capable of striking distant Allied bases or, most worryingly, massive aircraft carriers and fleet formations at sea.

The Ecological Catastrophe: 67 Tons of Poison

When the wreck was rediscovered, the historical drama instantly transformed into an environmental nightmare.

The Leak: The 1,857 steel flasks, once 5mm thick, had been slowly corroded by decades of saltwater immersion, becoming paper-thin. They were leaking a shimmering, silvery liquid directly into the marine environment.

Toxic Saturation: Scientific tests confirmed the devastating scale of the poisoning. Normal, clean ocean sediment contains about $0.1 \text{ mg}$ of mercury per kilogram. Near the wreck, investigators found a staggering $24,000 \text{ mg}$ per kilogram.

Food Chain Contamination: The toxic metal does not dissolve; it forms heavy beads that roll along the seafloor, entering the food chain, where it is absorbed by small creatures, passed to fish, and ultimately to humans. This necessitated a strict, permanent no-fishing zone around the site.

The Salvage Dilemma: Entombment Over Removal

The Norwegian government faced an unenviable task: what to do with a toxic, explosive puzzle 150 meters down.

The options were stark:

Full Salvage: An audacious, multi-million dollar plan to raise the entire unstable wreck and its fragile, explosive cargo. This was the most complete solution, but the risk was immense. The unstable seabed and the danger of rupturing a flask during the lift—raining liquid poison through the water column—were deemed too great.

Encapsulation (Entombment): Burying the wreck right where it was, sealing its environmental threat while accepting that it would permanently seal the watery grave of 73 men.

Ultimately, the salvage plan was abandoned. The final engineering solution was to create an artificial seabed. The broken submarine was covered with a 12-meter-thick layer of special sand and gravel, topped with heavy rocks and concrete to prevent erosion. This practical, if somber, conclusion was deemed the least risky way to contain the environmental threat for the long term, finally sealing the submarine’s secrets beneath a protective shield.

The Human Cargo and the Uranium Myth

The U-864 was transporting not just metal and blueprints, but human expertise—four technicians whose skills were considered priceless:

Two Messerschmitt Engineers: Ralph von Klinganberg and Ricklef Schmerus, carrying the know-how to tweak, troubleshoot, and set up production for the jet engines in Japan.

Two Japanese Specialists: Tadaw Yamamoto (torpedo expert) and Toshio Nakai (fuel specialist), representing technical barter for Japanese expertise.

Their loss was both tactical and intellectual, erasing the experiment in technical diplomacy that could have fundamentally altered the war’s timeline.

Finally, the most persistent rumor—that U-864 carried uranium oxide for Japan’s atomic bomb project, similar to the cargo of the later-surrendered U-234—was investigated. Formal investigation of the cargo manifests and radiological scans performed by remote operated vehicles found no radioactive signature consistent with uranium oxide. The true danger was not an atomic weapon, but the 67 tons of metallic mercury and its devastating effect on the marine ecosystem.

The mission ended in a loss of life and, decades later, a poisoned seabed. The documented truth of U-864 is a complex and sobering reminder of how industrial skill was militarized in extremis, and how its violent end created a lasting environmental catastrophe.