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Norway’s Heroic Heavy Water Sabotage

28th of February, 1943. Norway

Norway’s Heroic Heavy Water Sabotage On a bitterly cold night in February 1943, nine Norwegian spies waited in the mountains above the Vemork heavy water plant near the small town of Rjukan, Norway. Their mission was to knock it out of action. It wouldn’t be easy. To get there, they had three options: walk through a minefield; force their way over a narrow bridge guarded by Germans; or cross a partially-frozen river, then scale a 500-foot cliff.

After Germany’s invasion of Norway in April 1940, the Germans seized Norsk Hydro’s Vemork plant just outside of Rjukan. Desoute the Vemork plant’s original design to use mountain water for electrolysis to produce ammonia for nitrogen fertilizer. The plant had recently become the first industrial-scale production site of heavy water in the world and the Allies would need to destroy it with a covert operation.

King Haakon VII, Prof. Leif Tronstad (front, left), Capt. Harald Sandvik, Crown Prince Olav at SEO Training Facility in Scotland (1944). Photo Credit: By Henrikaamodt (Own work) [CC BY-SA 4.0 (], via Wikimedia

They chose the cliff…

The Vemork plant produced heavy water, which contains a very rare form of hydrogen. Heavy water can be used in a reactor to create plutonium-239, which in turn is used to make nuclear weapons. One of Vemork’s designers was chemistry professor Leif Tronstad. When the Nazis invaded Norway, Tronstad began working as a secret intelligence agent for the British. But the Gestapo quickly became suspicious, and Tronstad fled to the U.K. for safety. He told the British everything he knew about the plant.

When the British began planning an attack on the Vemork facility, Tronstad told them that critical components of the plant were in stone- and steel-walled rooms deep in the basement. Bombing the plant would be useless. Instead, they planned a risky covert operation. The facility was surrounded by minefields and barbed-wire fences, and protected by armed guards. It was only accessible by a single road, which passed over a heavily guarded suspension bridge.

Initial operations

The first phase of the British plan to destroy Vemork—called Operation Grouse—was in October 1942. A scout team of Norwegians parachuted into the area surrounding the plant to gather information and prepare for an attack. The small Norwegian team lived off the land and hunted reindeer to survive in the freezing wilderness.

While the surveillance team continued their mission, the British sent another team to destroy the plant. Thirty-nine troops were dropped near Vemork in two military gliders. The weather was rough, and luck was not on their side. One of the gliders crashed into a mountain, killing everyone on board. The other crash-landed far from the intended destination. Some of the soldiers on board died in the crash, and the survivors were rounded up and executed by the Gestapo.

Airspeed Horsa – British Glider Plane Type Used in Operation Freshman. Photo by Royal Air Force via the website/ Public Domain.

Operation Gunnerside

On February 16, 1943, the Grouse group was still in the field. Six more Norwegians parachuted in to join the operation. Among them was Joachim Rønneberg, the new leader of what came to be called Operation Gunnerside. It took five days of travel in a blizzard for the two groups to meet.

Finally, on February 27, they were ready for the raid on Vemork.

Rjukanbanen (Rjukan Train Line) from Rjukan towards the power plant at Vemork, Norway. Photo Credit: Anders Beer Wilse [Public domain], via Wikimedia Commons.
Rjukanbanen (Rjukan Train Line) from Rjukan towards the power plant at Vemork, Norway. Photo Credit: Anders Beer Wilse [Public domain], via Wikimedia Commons.

The nine men crossed the half-frozen river. They climbed 500 feet up the cliff to arrive at the plant. They had remained undetected. Four of the men served as the explosives group, and the other five were the cover squad. They cut the lock on the outside gate. The explosives group had planned to use a side door to enter the plant—but it was locked. The man who was supposed to unlock it was sick and hadn’t shown up to work. Luckily, they had a backup plan—Tronstad had described a tunnel that led to the heavy water cells.

Rønneberg found the tunnel. He and another man went through and seized the watchman. While holding the watchman hostage, they positioned explosives around the heavy water cells.

At the last second, Rønneberg shortened the fuses to the explosives from two minutes to just thirty seconds.

Reconstruction of the Operation Gunnerside team planting explosives to destroy the cascade of electrolysis chambers

He wanted to be able to hear the explosion as they escaped to safety. The explosives group fled the plant and reconnected with the cover group on the mountain plateau. None of the nine men were caught. The operation was a success.

From the left: Knut Haukelid, Joachim Rønneberg, Jens Anton Poulsson shaking hands with HM King Haakon VII of Norway (1948). Photo Credit: Leif Ørnelund [CC BY-SA 4.0 (], via Wikimedia Commons.

Success was short-lived: the Germans had the production facility back up and running just a few months later.

But the Allied forces were determined to destroy the plant, and, in November 1943, American bombers hit the plant hard.

Even though the key heavy water components survived the bombing, the Germans decided to move production from Norway to Germany. They were blocked again when another group of saboteurs blew up the bow of the ferry D/F Hydro.

The SF Hydro at Mæl in 1925

Norway’s Heroic Heavy Water Sabotage Written by Kim Hansen