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Norwegian Resistance Coup
by Ray Mears

Hitler's Sunken Secret homepage

Between 1940 and 1945, thousands of young Norwegians fought in Norway's Resistance movement against the occupying Nazis. More than 2,000 of them, both men and women, died in action, by execution, or in concentration camps. Perhaps the most daring Resistance attack, which Ray Mears describes here, was a successful late-night raid that nine Norwegian saboteurs made on the Vemork heavy-water plant on February 28, 1943, over a year before the sinking of the Hydro ferry. Click on highlighted names for brief bios.


At exactly 0030 hours, they advanced towards their objective.

All nine crept silently to a store shed about a hundred yards from the giant wire-mesh gates. The covering party took up their positions clutching their tommy guns, while Haukelid ran forward and snapped the thick chain lock using Ronneberg's wire-cutting shears. It took just one cut and a few seconds to break into one of the most strategically important institutions in the entire theatre of the Second World War.

As the chain slackened the covering party poured forward, rushing inside the compound and taking up fresh positions. They were all carrying chloroform in their pockets to overwhelm any guards they found on patrol. The demolition party, meanwhile, forced open a second gate, about 30 feet below on the level leading to the basement, where the high-concentration heavy water cells were positioned.

The factory rumbled but otherwise all remained quiet. The only cause for concern was the bright moon, which had broken out from behind the clouds, and the lights from inside the factory, which had been poorly blacked out. The darkness they cherished had deserted them. When Ronneberg gave the sign the covering party took up their allotted positions close to the hut housing the German guards. Leaving one man on guard, the remaining four members of the demolitions party split into pairs, as planned, with each carrying complete sets of explosives lest one team should fail to reach the heavy water.


They headed straight to the cellar door, but finding it locked they tried a second entrance on the floor above; that too was secured. (The cellar door was meant to have been left unlocked by one of Skinnarland's contacts at the plant, but he had fallen ill and was unable to come to work that day.) As they looked down into the cellar below they could see a scientist going about his work, but there was no sign of Germans inside the factory.

There was only one option left if they were to avoid a firefight and that was through a narrow cable shaft Professor Tronstad had told them to use as a last resort. Thank heavens for the meticulousness of the professor! Sure enough, the hatch was open just as Tronstad had said it would be. When Ronneberg looked around only Fredrik Kayser was at his shoulder, the other pair (Idland and Stromsheim) having got separated from them during the search.

Conscious that every minute was now crucial, Ronneberg and Kayser climbed a short ladder and crawled as silently as possible down the shaft on their hands and knees over a mass of wires and pipes, pushing their sacks of explosives ahead of them as they went. Through an opening in the ceiling they could see the target beneath them. At the end of the tunnel the pair quickly slid down a ladder into an outer room before rushing the night watchman inside the high-concentration area.


They immediately locked the doors and Kayser held his gun to the night watchman, who was quivering uncontrollably. He had probably never seen a British army uniform and he certainly would not have expected to see one here. Ronneberg tore open his rucksack and began placing the sausage-shaped explosive charges on each of the cylinders, which, down to the very last detail, were exactly the same as the models they had used in the reconstruction back in Britain.

Ronneberg had laid about half of the 18 charges when he heard a shattering of glass, and he spun around to see Sergeant Birger Stromsheim climbing in through a window from the back of the plant. Kayser also swung around and prepared to load his gun before he realized they were in good company. It was an alarming moment, and only heightened the mounting tension they all felt as they rushed to complete their task. Stromsheim and Idland had been unable to find the cable duct and, unaware that Ronneberg and Kayser were already inside, had decided to take the only route left to them. It was a brave but risky move. The noise of the shattering glass might well have alerted the Germans to the raid. Ronneberg cut his hand as he rushed to remove the rest of the broken glass so that Stromsheim could get in.

Outside the broken window Idland kept watch as Stromsheim helped Ronneberg secure the final charges and then checked them over twice while his leader laid the fuses. Originally, they planned to set two-minute fuses, but fearing that someone inside the plant might undo their work, they laid two extra 30-second Bickford fuses as a precaution. This was a brave move because it meant that the alarm would be raised before they were out of the plant complex. Ronneberg's appetite for a fight with the Germans was remarkable, his commitment total: first he wanted to fight his way across the bridge, now he took another option for the good of the operation, which he had every reason to believe would lead to a blazing gunfight.


Just before they lit the fuses, the guard said, "Please, I need my glasses. They are impossible to get in Norway these days." It was a surreal moment and the request stopped the three raiders in their tracks, bewildered by this change to the script, this brief snapshot of civilian anxiety at the critical point of a crucial military operation. There followed a few curious moments as the saboteurs politely rummaged around his desk for his glasses. "Takk" (thank you) said the smiling guard as he put the spectacles on his nose. As he spoke, the four of them heard the sound of footsteps approaching. Was this one of the German guards making his rounds? To their relief, a Norwegian civilian walked into the room and almost fell backwards as he saw what appeared to be three British commandos and his colleague with his hands above his head.

“It sounded like two or three cars crashing in Piccadilly Circus.”

Outside, the covering party were growing twitchy. Twenty-five minutes had passed since the demolition party had disappeared into the shadows of the great building. Storhaug was detailed to cover the two guards on the suspension bridge, and as he crouched in the darkness he could hear them chattering idly, utterly oblivious to the historic drama being played out just a few dozen yards away.


As Ronneberg lit the fuses, Kayser counted to 10 before ordering the two civilians to run upstairs as fast as they could. The raiders then rushed out of the steel cellar door into the night. When they were no more than 20 yards away they heard the dull thud of the explosion. The sound was muffled by the noise of the power station and the thick concrete walls, and the covering party wondered whether the demolition party had laid the charges properly. But Ronneberg knew from the sound that the cylinders had been destroyed and that 3,000 pounds of heavy water—about four or five months' production—would be awash on the basement floor, flowing towards the drains.

Unknown to the saboteurs, the sound of a dull thud was not uncommon to those who worked or lived at the Vemork installation. Small, harmless explosions in the combustion machinery would occasionally be heard, while cracking ice or a heavy collapse of thawing snow somewhere along the steep slopes could also generate a similar noise. "The explosion itself was not very loud," recalled Poulsson. "It sounded like two or three cars crashing in Piccadilly Circus."


The four members of the demolition party immediately took cover, waiting for a reaction from the German barracks hut. They lay or stood stock-still as the door of the hut swung open and a soldier appeared, only half dressed, flashing a torch around the factory yard. He walked slowly in the direction of Haukelid, who was hiding behind some empty drum caskets.

When he was five yards away he stopped and swept the beam of the torch no more than a few inches above the Norwegian's head. Had it been a windless night, he might have been able to hear his heavy breathing, if not the rapid hammering of his heart. At that exact moment, three tommy guns and four pistols were pointing straight at the back of the unsuspecting German. A couple of inches lower with his torch and he would have been riddled with several dozen bursts of Allied firepower. But he turned on his heel and walked slowly back to the hut, and as the door shut the order for withdrawal was given.

Editor's postscript: While they succeeded in destroying the heavy-water stocks and all nine saboteurs made it to safety, the Nazis had the heavy-water apparatus up and running a mere five months later, instead of the one to two years the raid's plotters had hoped for. In the end, however, the Germans never succeeded in using the heavy water to make an atomic weapon (see Nazis and the Bomb).

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Vermork in 1930

The Vemork heavy-water plant as it appeared in 1930. The saboteurs snuck down after dark from the Hardanger Plateau high above.

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Sketch of plant

This sketch, based on information provided by Norwegians who worked in the plant, shows the route the saboteurs had planned to take into the basement where the heavy water apparatus lay. As it turns out, they had to choose a different means of access.

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Factory side

The Vemork electrolysis building appears here in a photo taken during the plant's inauguration. After descending from the plateau, the attackers crossed the gorge behind where this photographer stood and approached the plant from alongside the turbine hall (upper left).

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Group photo

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.

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The explosion ripped apart the cylinders holding the heavy water, causing the precious liquid to run down the drains.

Hitler's Sunken Secret
Nazis and the Bomb

Nazis and the Bomb
How close were the Germans to a nuclear weapon?

Norwegian Resistance Coup

Resistance Coup

A midnight raid was the masterstroke of a broad insurgency.

See the Spy Messages

See the Spy Messages
Read the actual telegrams sent between Norway and London.

Dangerous Water

Dangerous Water
What is heavy water, and what makes it a threat?

Ray Mears Ray Mears is a wilderness survival expert, a host of popular TV series in his native England, and author of, among other books, The Real Heroes of Telemark (Hodder & Stoughton, 2003), from which this article was adapted with kind permission of the publisher.

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