Sabotage at Vemork: The Norwegian Epic. A blend of high politics, military drama, scientific adventure and individual courage is one way to concisely define the Sabotage that took play at Vemork Hydroelectric Power Plant in Norway during the Second World War. Before jumping to the operation itself, we’ll indulge in giving out the outline of the whole happening first. Let’s begin.

The what and why


Germany invaded Norway in April 1940- resistance was crushed brutally. The Nazis had developed keen interest in Heavy Water (Deuterium Oxide) and had found an ideal location to industrially produce it. Talking in layman terms, Heavy Water is used to moderate the speed of neutrons for an efficient Nuclear Fission. High speed neutrons in absence of a Moderator do not kickstart a chain reaction which is a primary requirement for such a process. It is true that Pure Graphite can also be used as a moderator and the Americans used it in those days. However, at the outset America had no facility to produce Heavy Water (superior to Graphite) and would only begin to use it much later. Germany had a clear upper hand here- captured Norway already had had such a facility. Heavy Water now became an indispensable requirement to any kind of Nazi Nuclear ambitions.

The plant had been built by Norsk Hydro in 1934 at Vemork in a very inaccessible part of Norway which used to be a godforsaken valley at that time. Sun rays disappeared for most months during the winter and whatever light that could reach the deep gorges was blocked by the high mountains.

Photo by J. Gallardo Canabes
Photo by J. Gallardo Canabes

You may ask why in all the places in Europe was Vemork chosen. The simple answer to this is cheap hydroelectric power. Cheap, not only because there are high falls and rapids in Norway- Alps too are endowed with this- but cheap because the mountains contain huge lakes and water reservoirs which is essential for such a plant. Heavy Water is not “made” but is isolated from ordinary water.

Electrolytic Cell Chamber at Norsk
Electrolytic Cell Chamber at Norsk

Yes, a tonne of ordinary water contains about 150 grams of Deuterium Oxide. Only the process of electrolysis could significantly extract the moderator and such a system already existed before the Nazis came to log their heads. Water all around the facility made it even more attractive. It was a best case scenario for Hitler, and soon expanded the number of electrolytic cells from 9 to 18 thus doubling the plant’s production of Heavy Water.

The Allies were becoming increasingly worried, not because they knew anything specific about Germany’s nuclear project but because their own nuclear research was advancing, aiming precisely at building an Atomic Bomb. The elephant in the room- Was Germany going to do the same? Was this an arms race? This was reason enough to propel the British Special Operations Executive (SOE) and Secret Intelligence Service (SIS)-who were tasked to take out subversive operations in Axis occupied countries- to chalk out a plan and put an end to production at Vemork. SOE was also called Churchill’s Secret Army and charged by him to “set Europe ablaze”. Cheesy huh?

Operation Grouse/Freshman

On 19 October, 1942 an advance 4 man team of Norwegian commandos was para dropped in the area. Since the drop had been inaccurate, the British became suspicious when the team contacted them.

“What did you see in the early morning?”, asked the SOE Handler

“Three Pink Elephants”, exclaimed the Commando.

It had now been ascertained that now the primary party of Royal Engineers could be dropped via gliders in a month who would undertake demolition at the Hydroelectric Plant. On November 19, 1942 two Halifax aircraft left Scotland, each towing a glider. A complete disaster followed. Of the total 4 aircraft, only one Halifax returned to Scotland. The others crashed in lieu of extremely bad weather. The Gestapo rounded them up, tortured them and finally executed them implementing Hitler’s Commando Order. 41 brave men lost their lives.

royal engineers
Royal Engineers. Photo by Peter Yeates

The 4 Man team survived off moss and lichens in the formidable winter before finally shooting a reindeer. To add to the pain, Nazis had become aware of Allied attempts to interrupt working of the Plant and increased defenses with floodlights, deadening mines and additional troops.

Operation Gunnerside

A little more than a week after the debacle, Joachim Ronneberg, a Norwegian First Lieutenant while in Scotland was contacted by London through his CO and asked if he would want to lead an expedition to Norway. Accepting gladly, he was also asked to select 5 men for the job. Initial plan was to drop the Team in December only. That meant about a fortnight for the Team to prepare themselves with equipment, their trip to Sweden, to familiarize with explosives and the target. Time was painfully less. In those days, items for a winter expedition like a sleeping bag which could withstand -30º C frost wouldn’t magically appear in shops. It is interesting how appropriating the smallest of items was an arduous task. Tommy Guns and Colt .45 was chosen as they were reliable to get the strongest possible hit on the spot. They also shared the same ammo.

Major Tronstad showed me a photo of our target. I had never been to Vemork before, and it was an impressive target, I must say.

Joachim Ronneberg
Joachim Ronneberg

The photo showed the gorge and the suspension bridge, and the road leading up to the factory area. The plant itself was a huge building – 25 x 100 metres – seven stories high (35 metres) concrete. Our target, the heavy water factory, was down in the cellar.

December full moon and a failed attempt to land in January pushed the infiltration date of the “Gunnerside” Team to 17 February, 1943. Again, the  para drop had been inaccurate and the Team was 25 KMs off-course. There was a further delay of 5 nights due to extensive snow storms.

Hardanger Plateau. This was traversed by the Gunnerside Team.
Hardanger Plateau. This was traversed by the Gunnerside Team.

When the Team met the 4 Man advance party which had landed back in October (called the Swallow  Team now), the ultimate planning was done.

I must say I do not think that any group sent into Europe was supplied with such good intelligence. I could sit there with a blank piece of paper and draw a map of the area, including the roads and buildings and tell them that according to the latest reports which they had brought up from the valley, from our local contacts at Norsk Hydro.

About 20 soldiers were in a barrack near Norsk Hydro and there was a double guard at the only bridge connecting the facility to the valley. There was also a gate in the middle of the bridge with a sentry and an alarm which would alert guards back at the plant.

Notice the gorge below the Suspension Bridge. Photo by Michael Spiller
Notice the gorge below the Suspension Bridge.
Photo by Michael Spiller

Everything was fenced in and there were mines along all the water pipelines except the Railway entrance at the southern end. Initially the group planned to scale down the slopes from the mountains between Vemork and Rjukan or  to cross the gorge below the bridge. Local guides did not support any of these terming them “impossible”. Their solution was to mingle with the shiftworkers when they came up at 10 P.M. and get rid of the sentries on the suspension bridge. Fearing that the Norwegian workers would be shot the next day by Germans, the path through the gorge was chosen. After further study of photos and reconnoiter by one man, easy spots to traverse were discovered. Naturally, the group now saw themselves succeeding in their objective.

The team set out on the night of 27 February, 1943. Workers were to be avoided at all costs. Joachim Ronneberg, leader of the team said

To avoid some workers’ buildings, we decided to go straight out into the valley, which meant a lot of climbing. I remember at one point, the bus with the shiftworkers passed by. Two of my men who were hiding above the road, waiting for the bus to pass, nearly fell down onto the roof of the bus. But it turned out all right.

Keeping the climbing equipment aside, the group reached peripheral fence with their weapons and explosives by 11.30 P.M. After closely watching the change of guard at the barracks, when the clock went past midnight, the barbed wire and fence was cut. The covering party went around the barracks and positioned themselves.

The main building which housed the cellar in the basement
The main building which housed the cellar in the basement

The demolition party climbed down and entered the building (in picture). Underneath the roof, a cable tunnel was found which was 5 meters high. There were 7 stories in all and the production began right from the top floor and went down in circles to the cellar-the last stage of production containing the 18 electrolytic cells-which was the target. Two of the five managed to get in and started laying the charges. The remaining had to break in through a window- the ones inside must have skipped a heartbeat. The charges were small, weighing 4.5 Kilos each and had already been chained by the British. A Norwegian workman, who was filling the logbook overheard the group who were in a dilemma whether to put a 2 minute  or a 30 second fuse. The workman was approached by the men for the key of the cellar door which they got after a brief search for the man’s glasses. Since the workman was glad to help the group, Ronneberg decided not to lock him up in the lavatory when escaping as was advised by his CO, Major Tronstad. Charges were placed with a 30 second fuse, as they wanted to hear the bang and the workman was told by Ronneberg to run up the staircase, lie down and keep his mouth open until he hears the bang.  Ronneberg said,

Damaged cylinders at the plant
Damaged cylinders at the plant

I know that he kept his mouth open, because he could hear when I met him two years later. Other-wise, if he had had his mouth closed he would have blown out his eardrums.

The demolition party was to rendezvous with the covering party at the river (below the bridge) but because of the 30 sec fuse met them at the gate just outside only, surprising them. A Tommy gun was left at the premises to assure the Germans that this was a British job and prevent reprisals.

What was astonishing was that Germans did not have a clue of what happened. Both parties now began to move out and the alarm went off when they reached the river. When they reached the road on the other side, they spotted several cars moving towards the plant. Since guards on the bridge reported that there had been no activity, the Germans concluded that the intruders came from the southern side of the plant. What is more interesting that Germans believed there were 3 intruders when in actual there were 9 members in the group. Nothing was done to check the northern side at all, giving the Gunnerside Team the much needed to time to escape. Joachim Ronneberg explained,

Later on I heard that their main theory was that we had come to Vemork as civilians, had put on uniform for the operation, dressed in civilian clothes afterwards and tried to go by ordinary communication lines towards Oslo. So that was where they started to search.

Still from the movie, Kampen om tungtvannet
Still from the movie, Kampen om tungtvannet (1948)

It took about 3 hours from the explosion for the Team to reach the mountainside from they would ski the rest of their journey. Sunrise awaited the men when they reached. The Gaustadtoppen mountain peak on the other side was lit in the red morning light. It was a marvelous view, and for the team leader Ronneberg a marvelous situation. Not a shot was fired, heck the guns were not even loaded. There were no casualties. The explosives did not fail them. The Germans did not have the faintest idea where the intruders went.

A sight to weary eyes, the Gaustadtoppen mountain. Photo by Halvor Mork
A sight to weary eyes, the Gaustadtoppen mountain. Photo by Halvor Mork

I remember we were sitting there eating biscuits and chocolate, and nobody said anything at all. I think everybody had quite enough with his own thoughts.

The group now moved to where the Swallow group had it’s headquarters. Five among them were ordered to go to Sweden for further orders. The men took part in more resistance operations in Norway until their homeland was freed by the allies. Altogether, 11 men who were part of the operation which includes the Swallow and Gunnerside teams along with the chaps down in the valley who were their contacts survived the war and lived to tell the tale.

Surrounding their boss Leif Tronstad (front row, center) are most of the Vemork saboteurs, including (front row left to right) Jens Anton Poulsson and Joachim Ronneberg, and (back row left to right) Hans Storhaug, Fredrik Kayser, Kasper Idland, Claus Helberg, and Birger Stromsheim.
Surrounding their boss Leif Tronstad (front row, center) are most of the Vemork saboteurs, including (front row left to right) Jens Anton Poulsson and Joachim Ronneberg, and (back row left to right) Hans Storhaug, Fredrik Kayser, Kasper Idland, Claus Helberg, and Birger Stromsheim.


The plant was destroyed for one and a half to two months and production was halted for five months. America planned to bomb the facility and on 16 November 1943, 173 B-17 and B-24 Bombers swept over the Rjukan valley and rained metal on the plant at Vemork. The factory, power station and the pipelines took a beating but the immediate target of the cellar remained practically untouched. The Germans realized that it would be safer to carry out their operations in Fatherland itself and started to move out the produced Heavy Water.

SF Hydro
SF Hydro, the ferry carrying Heavy Water was sunk in the deepest part of Lake Tinnsjo

The ferry which was carrying the precious cargo on Lake Tinnsjo east of Rjukan was blown up by another Norwegian resistance party on 20 February 1944. All the cargo sank to the bottom of the lake. Later in 1944, Germany dismantled it’s Heavy Water apparatus and sent it back to Germany. They had more important things to pay attention to after D-Day. Both the operations in the aftermath saw loss of civilian life.

A different perspective

On further analysis of events, it is only paradoxical that Allied efforts to dismantle the plant had only modest effect on the overall German nuclear program. Why?

BECAUSE GERMANY HAD GIVEN UP ON THE A-BOMB IN 1942 ITSELF , much before Allied special efforts. German scientists were certain that they wouldn’t be able to make the bomb before the end of the war. It would be a wasteful allocation of resource when much of it could be used for the other German war efforts. The embryo of pessimism grew in all levels of military and scientific circles. Note that America with it’s enormous resources with no enemy on it’s territory could only come up with a bomb by July 1945! Albert Speer, Minister of Armament in his memoirs wrote,

On the suggestion of the nuclear physicists we scuttled the project to develop an atomic bomb by the autumn of 1942, after I had again ·queried them about deadlines and been told that we could not count on anything for three or four years. The war would certainly have been decided long before then.

Against this background, it becomes clear that the presence or absence of the Norwegian sabotage had no effect on the final outcome. It is also true that since Germany only received half of the Heavy Water-they could not use Uranium for energy purposes also. However, there was no bomb ever planned.

So does did strip Norway of it’s national history which they cherish? Definitely not. War is a hidden game. At that point, the intelligence which the SOE and SIS possessed only added fuel to thought that Germany was moving towards a bomb. In those already dark days, it was a perfectly human and intelligent effort to paralyze Germany’s nuclear ambitions. We are in a position to judge, looking at the whole situation from a postwar perspective. They were not.

Whatever be the outcome- the saga of the sabotage does not loose any of it’s thrill, the saboteurs none of their valor, the action none of it’s audacity of design even if hindsight puts the actions in a different perspective from that which prevailed during the war. The whole plan was fought on assumptions during war and remain as successful and as gallant as they ever have been.

Joachim Ronneberg is the final surviving member of the Gunnerside team. Defensionem community wishes him an even longer life and salutes the entire team for their heroic effort.


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