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Nuclear Weapons

Sabotaging the Nazi Bomb

February 20, 2018

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.

They chose the cliff.

The Vemork plant in Norway.

The Vemork plant in Norway produced heavy water, which can be used in a reactor to create plutonium. The plant is set into a high mountain plateau known for frigid and unpredictable weather.

Norsk Hydros fotosamling/NIA

Heavy water and nuclear weapons

Heavy water can be used in a reactor to create plutonium-239, which in turn is used to make nuclear weapons.

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.

Venmork designer Leif Tronstad.

Leif Tronstad helped design the Vemork facility. His knowledge of the plant allowed the British to find a way to destroy it.

Schroeder Archive/Sverresborg Museum

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.

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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.

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.

A reenactment scene of Operation Gunnerside.

A reenactment scene of Operation Gunnerside. In addition to their mission, the men faced brutal winter conditions.

Leif Tronstads fotosamling/NIA

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

Vemork heavy water plant.

A view of the Vemork heavy water plant. The surrounding area is covered in snow.

Norwegian Industrial Workers Museum

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—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.

Freedom and peace

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 transport ship.

You have to fight for your freedom and for peace. You have to fight for it every day, to keep it. It’s like a glass boat; it’s easy to break; it’s easy to lose.

Joachim Rønneberg, Norwegian Army officer and leader of Operation Gunnerside

In the end, the Nazis failed to produce a nuclear weapon. The nine Norwegian men of Operation Gunnerside were a key part of what stopped them.

Nuclear History: World War II

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