Vemork Hydroelectric Plant as it looks today. A Special Operations Executive (SOE) Team in 1941 (Operation Gunnerside) blew up heavy water production equipment in order to sabotage the German efforts towards an Atomic Bomb. Credit: Skotten / CC BY-SA 3.0 DEED.

Operation Gunnerside was a World War II mission that aimed to halt German heavy water production via hydroelectric plants in Nazi Germany-occupied Norway. The operation involved both Norwegian commandos and Allied bombing raids. The operation was named after the village of Gunnerside, where the head of the British Special Operations Executive (SOE) had a family estate.

Heavy water was used in World War II as a moderator in nuclear reactors to slow down neutrons and increase the likelihood of nuclear fission. The Allies sought to inhibit the German development of nuclear weapons with the removal of heavy water and the destruction of heavy-water production plants.

Special Operations Executive

The SOE was a secret British World War II organization, officially formed on 22 July 1940. It was established under the Minister of Economic Warfare, Hugh Dalton, by amalgamating three existing secret organizations. The SOE’s mission was to conduct espionage, sabotage, and reconnaissance in occupied Europe and later in occupied Southeast Asia against the Axis powers, and to aid local resistance movements.

The SOE was also known as “the “Ministry of Ungentlemanly Warfare”. It directly employed or controlled more than 13,000 people, about 3,200 of whom were women. The agents of the SOE were mainly tasked with sabotage and subversion behind enemy lines. The SOE was dissolved on 15 January 1946, but its innovative methods and the bravery of its agents left a lasting legacy in the field of espionage and special operations.

Background

The hydroelectric power plant at Vemork was built in 1934. It was the world’s first site to mass-produce heavy water (as a byproduct of nitrogen fixing), with a capacity of 12 tons per year. Before the German invasion of Norway on 9 April 1940, the French Deuxième Bureau removed 185 kilograms (408 lb) of heavy water from the Vemork plant in then-neutral Norway. The plant’s managing director agreed to lend France the heavy water for the duration of the war. The French transported it secretly to Oslo, then to Perth, Scotland, and then to France. The plant was still capable of producing heavy water, however, and the Allies were concerned that the Germans would use the facility to produce more heavy water.

Between 1940 and 1944, a series of sabotage actions by the Norwegian resistance movement and Allied bombing ensured the destruction of the plant and the loss of its heavy water. These operations — code-named Grouse, Freshman, and Gunnerside — knocked the plant out of production in early 1943.

Operation Grouse & Freshman.

Operation Grouse was a sabotage raid against the Vermork heavy water plant in Norway during World War II. The operation was carried out by Norwegian commandos and British commandos, who landed in gliders and assaulted the facility under Operation Freshman. The objective of the operation was to destroy the heavy water production capabilities of the plant, which was being used by the Germans to develop nuclear weapons.

The operation was divided into two phases. The first phase, codenamed Operation Grouse, was made up of four SOE-trained Norwegian commandos who would parachute into Norway, conduct reconnaissance, and secure a landing zone for a 34-man team of British commandos, codenamed Operation Freshman. The second phase involved the assault on the plant itself.

The operation was not entirely successful, as the gliders carrying the British commandos crashed, and the surviving commandos were captured and executed by the Germans. However, the operation did provide valuable intelligence for future operations against the plant.

Operation Gunnerside

The British authorities knew that the Grouse team was still operational, so they planned another operation with them. The Grouse team code name had been changed to Swallow by then. On 16 February 1943, a Halifax bomber from RAF Tempsford dropped six more Norwegian commandos by parachute in Operation Gunnerside. They landed safely and met up with the Swallow team after several days of skiing across the terrain. The joint team finalized their plans for the attack, which was set for the night of 27–28 February 1943.

The Swallow team had done a thorough survey of Vemork’s security and found it daunting. The Nazis had fortified the area with mines and traps on the hill above the plant after the Freshman raid. The only way to the facility was a narrow bridge with extra guards. The commandos noticed a possible entry point, but it was not easy.

The ‘vulnerable spot’ was a 660-foot gorge that was so perilous that the Nazis ignored it. Claus Helberg, one of the Swallow members, discovered a path to go down the gorge, cross the river, ascend the other side, and reach Vemork without being detected.

On the night of 27–28 February, the commandos climbed up the cliffs of the massive gorge below the plant, slipped in, set explosives that destroyed the heavy water inventory (about five months production) and production machinery, before quickly fading away into the surrounding mountains. The team wore British Army uniforms to avoid reprisals by the Germans on the civilian population in the event they were killed or captured. They also carried cyanide capsules to rake in the event of capture. The commandos managed to destroy the production facility and escape without firing a single shot. 

The commando raid was followed by Allied bombing raids. The Germans ceased operations and attempted to move the remaining heavy water to Germany. Norwegian resistance forces then sank the ferry carrying the heavy water, the D/F Hydro, on Lake Tinn.

The Germans were taken aback by the success of the commandos. The destruction of the heavy-water production facility at Vemork was a significant blow to their nuclear program. The Germans attempted to move the remaining heavy water to Germany, but Norwegian resistance forces sank the ferry carrying the heavy water, the SF Hydro, on Lake Tinn.

The commando raid on Vemork was depicted in Operation Swallow: The Battle for Heavy Water (original title: Kampen om tungtvannet, French title: La Bataille de l’eau lourde) is a Norwegian-French film from 1948. The film is based on the true events of the Norwegian resistance fighters who sabotaged the Nazi-controlled heavy water plant at Vemork, with many of the participants playing themselves,

Operation Gunnerside was a significant achievement in the Allied effort to halt German heavy water production. The mission was successful in destroying the production facility and preventing the Germans from producing more heavy water. The operation was a testament to the bravery and skill of the Norwegian commandos and the Allied forces who participated in the mission. Operation Gunnerside has been widely praised as one of the most spectacular and important covert operations of the war.

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