• Si Biggs

Norwegian heavy water sabotage 'Heroes of Telemark'

Unit/ Formation: Combined Ops


Location: Norway


Period/ Conflict: World War II


Year: 1943


Date/s: 1940 - 1943


When they learnt that the Nazis had embarked on an atomic weapons programme the British were prepared to take considerable risks to disrupt it. The main target was the Vemork Hydroelectric Plant at Rjukan in Norway which was producing ‘heavy water’ essential for the Nazis to progress with their programme.


In Operation Grouse, the British Special Operations Executive (SOE) successfully placed four Norwegian nationals as an advance team in the region of the Hardanger Plateau above the plant in October 1942.


Vemork Hydroelectric Plant at Rjukan, Norway in 1935. In the front building, the Norsk Hydro hydrogen production plant, a Norwegian Special Operations Executive (SOE) team (Operation Gunnerside) blew up heavy water production cells on the night of 27/28 February 1943 in order to sabotage the efforts of the German nuclear energy project.

The unsuccessful Operation Freshman was mounted the following month by British paratroopers; they were to rendezvous with the Norwegians of Operation Grouse and proceed to Vemork. This attempt failed when the military gliders crashed short of their destination, as did one of the tugs, a Handley Page Halifax bomber. The other Halifax returned to base, but all the other participants were killed in the crashes or captured, interrogated, and executed by the Gestapo.


During exhumation in 1945, it was discovered that those executed had their hands tied behind their backs with barbed wire.


In the wreckage of a glider, the Germans discovered a map of the Telemark area with Vemork in a red circle. They immediately carried out a defense check of the Norsk hydra. However, they mistakenly thought that the real goal was to be a new dam, which was built near the factory, and therefore did not strengthen the patrols of the Norsk hydra.


The men of Operation Gunnerside. Leif Tronstad is bottom centre, Rønneberg bottom right. Source: © Norway’s Resistance Museum

The advance team for Operation Freshman, four Norwegians who had parachuted into the country before the gliders, had survived the winter by living off reindeer and moss. It was a notable feat of survival.


First we ate lichens under the snow. If reindeer can feed on them, that will be enough for us. We didn't like it very much, but after about two weeks, around Christmas, we saw the first reindeer and went hunting. After 1-2 days, we killed the first reindeer, and that saved us.

Three months after the first attempt, the Swallow group received word from Britain that six more Norwegians would be sent to Rjukan for Operation Gunnerside. Unlike in Operation Freshman, the special forces group was a small group of Norwegian commandos from Company Linge. The group was supposed to parachute to their target zone rather than use a glider to land and meet up with the Swallow group before raiding the Vemork plant.


Led by Joachim Rønneberg, the group jumped from a plane under the cover of snowfall at around midnight on February 16, 1943. The commandos all dressed in British uniforms underneath their snowsuits; they reasoned that if the British were blamed for the sabotage rather than the Norwegian resistance, the local population would be less likely to face German repercussions. While the group survived the landing and avoided initial German detection, they landed miles from the planned target site. After traveling for about five days, the Gunnerside group connected with the Swallow group.



Late in the evening on February 27, 1943, the Gunnerside group began the raid on the Vemork plant. There were three ways to access the plant: 1) come down from the mountains above the plant, which was an area covered in minefields; 2) cross a heavily-guarded, single-lane suspension bridge; or 3) travel to the bottom of the gorge, cross a half-frozen river, and climb a 500-foot-high cliff. According to Rønneberg, the group voted to take the gorge, which led to a route alongside a railway line that a local contact said was relatively unguarded.


In order to get through the plant’s side gate fence, Knut Haukelid used a pair of heavy-duty metal cutters brought by Rønneberg. Fortuitously, Rønneberg had purchased the metal cutters in Cambridge, England after going to a movie on his day off. He told The New York Times that the handsaw provided by the British military “would have taken too much time, made too much noise and alerted Nazi guards.”


After getting through the fence, the group divided into their four-man explosives group and five-man cover squad. The explosives group planned to enter the plant through a side door. This door, however, was locked. Rønneberg was able to find an access tunnel and entered the plant with Fredirk Kayser.


He recalled to The Times, “Getting inside I was quite certain that the rest of the party would follow me, but only one chap came. The other ones hadn’t found the entrance to the tunnel. Therefore we decided we would have to do it ourselves and started laying out the charges.” After getting separated from their squad mates, the other two men on the explosives team, Kasper Idland and Birger Strømsheim, decided to break in through a window.


Once in the building, Rønneberg and his men placed two strings of explosive charges next to the heavy water production cells. In order to provide enough time to escape but still hear the explosion, he decided to shorten the fuses so that they lasted only thirty seconds rather than the designed two minutes. The explosion apparently was not as loud as expected, but nonetheless, Rønneberg heard it and knew the mission was a success.


After fleeing the plant and reconnecting with their cover squad, Rønneberg and the rest of the Gunnerside group began to ski toward Rjukan. Once they reached the mountain plateau, the group split up. In uniform and fully armed, the explosives team traveled more than 200 miles to Sweden on skis. The cover group, on the other hand, spread out throughout the plateau. Despite the Germans’ search and pursuit of the group, none of the members were killed or captured. Upon inspecting the damage to the heavy water facilities, General Nikolaus von Falkenhorst, the head of German forces stationed in Norway, referred to Operation Gunnerside as “the most splendid coup” (Bascomb, p. 213)


Joachim Ronneberg:

The main building was 25 by 100 metres in seven stories. The production started in the top storey and continued in circles until it ended as heavy water down in the bottom. And that was our target: a battery of 18 cells, the last stage in the production.
Two of us managed to get in and we started laying the charges. The order was that if anything happened that could endanger the result, you had to act on your own. The three other chaps in the demolition party, one of them carrying a set of charges, decided to break the window to get inside because they did not know that we were busy inside. When the window broke, both groups were equally surprised.
I helped one of my friends to get in, and we finished laying the charges. They were not big charges. They weighed about 4.5 kilos, and had been chained up by the British before we left. Two-minute fuses, four of them.
There was a Norwegian workman inside the factory reading the instruments and filling out the logbook. He heard us talking Norwegian, discussing whether we should put on a 30-second fuse just to be sure that we heard the bang as soon as possible.
That was when he asked for his glasses. It was difficult to get glasses in Norway, so he wanted to have them before we lit the charges. I remember I threw away what I was doing and searched for the glasses and found the case and handed it to him.
He was very pleased and I started getting the ignition sets ready when he suddenly said that the glasses were not in the case. I said “Where the hell are they then?” And he said “Well, they were there when you came in.” In the end I found them being used as a bookmark in his logbook, and gave them to him.
Then we ordered him to give us the key for the cellar door so that we could go out through the door like other human beings. We opened the door and I remember Major Tronstad saying that in case we needed to lock up the guard, the key for the lavatory was on the left-hand side of the door. I remember just after we had lit these 30-second fuses, I saw the key, but we did not need it.
We said to the man, “You just run around the corner, up the staircase, lie down and keep your mouth open, until you hear the bang. There will be only one bang, so when it is over you can go down and watch the result”. I do not know if he did. But I know that he kept his mouth open, because he could hear when I met him two years later. Otherwise, if he had had his mouth closed he would have blown out his eardrums.
We had planned to meet the covering party down by the river. They expected to be there a while after they heard the bang, not knowing that we had used only 30-second fuses, so we met them just outside the gate.
What astonished us was that the Germans did not understand what had happened at all. The covering party told us that one man came out of the doorway of the guard house with a torch, and made a sort of search around the house and went in again. When we got back across the river, we took a parallel road to the main road leading down to Rjukan centre. At the place where the funicular starts down in the valley, we began climbing a zigzag road leading up to the top. It was a rise of about six or seven hundred metres, and it took us, I would say, three hours from the explosion until we could put on our skis up on the mountainside.

Operation Gunnerside (later evaluated by SOE as the most successful act of sabotage in all of World War II) successfully destroyed the Vemork heavy water production facility and supplies. The raid caused the Germans to lose about 500 kg of heavy water and decommissioned the plant for a few months. The mission’s success, however, was not a final blow to the Germans’ heavy water production. By May 1943, the heavy water production facilities were rebuilt and operating again.


Even though bombing the plant was initially ruled out, the United States decided to bomb the Vemork plant following the Germans’ reconstruction of the heavy water facilities. On November 16, 1943, 140 American bombers flew over Rjukan and bombed the Vemork plant. According to Thomas Gallagher’s Assault in Norway: Sabotaging the Nazi Nuclear Program, the heavy water production facilities experienced minimal damage from the bombing (p. 168). Figuring the attacks would only continue, the Germans decided to stop producing heavy water at Vemork after the bombing. Unfortunately, there twenty-two Norwegian civilian casualties in the bombing raid, the tragedy Tronstad had hoped to avoid (Powers, p. 212).


D/F Hydro that operated between Rollag and Mæl as a railway ferry. Sunk by Norwegian resistance during World War II. Photo Credit: Anders Beer Wilse [Public domain], via Wikimedia Commons.

Germany’s attempt to move their heavy water supplies from Norway to Germany also ended in failure at the hands of Norwegian saboteurs. Led by Knut Haukelid, a group of Norwegian saboteurs was ordered to sink a ferry carrying the Germans’ semi-finished heavy water products to research centers in Germany. On February 20, 1944, the “Hydro” ferry was sunk by an explosion in the boat’s bow, and the Germans lost their last supplies of heavy water from the Vemork plant. There were four German and fourteen Norwegian casualties from the explosion.


Extracts from WW2 Today

127 views0 comments