Joachim Ronneberg, Who Led Raid On Nazi Atom Bomb Research Site, Dies At 99

The world loses a genuine war hero.

Joachim Ronneberg, a Norwegian soldier who led a raid that struck a crucial blow to Nazi efforts to develop an atomic bomb during World War II, has died at the age of 99:

The Norwegian saboteurs skied across the Telemark pine forest in winter whites, phantom apparitions gliding over moonlit snow. They halted at a steep river gorge and gazed down at a humming hydroelectric power plant where Nazi scientists had developed a mysterious, top-secret project.

Lt. Joachim Ronneberg, the 23-year-old resistance fighter in command, and his eight comrades — all carrying cyanide capsules to swallow if captured — had been told by British intelligence only that the plant was distilling something called heavy water, and that it was vital to Hitler’s war effort.

Hours later, in one of the most celebrated commando raids of World War II, Lieutenant Ronneberg and his demolition team sneaked past guards and a barracks full of German troops, stole into the plant, set explosive charges and blew up Hitler’s hopes for a critical ingredient to create the first atomic bomb.

Mr. Ronneberg, the last surviving member of the 1943 raid and one of the most decorated war heroes of a nation renowned for valorous resistance to the 1940-45 German Occupation, died on Sunday in Alesund, Norway, his daughter, Birte Ronneberg, said. He was 99.

A retired journalist and administrator for NRK, Norway’s public television and radio broadcasting company, Mr. Ronneberg and his saboteurs were showered with international honors after the war for what they had regarded as a suicide mission. It was celebrated in books, documentaries and films, notably Anthony Mann’s 1965 production, “The Heroes of Telemark,” starring Kirk Douglas, in what critics called a fact-flawed version of what had happened.

It was not until the war’s end in 1945 that Mr. Ronneberg learned the significance of the raid. “The first time I heard about atomic bombs and heavy water was after Americans dropped the bomb on Hiroshima and Nagasaki,” he told The New York Times in 2015. Had the raid failed, he concluded, London would have ended up “looking like Hiroshima.”

Historians have long debated how close Hitler came to nuclear weapons. A German writer, Rainer Karlsch, claimed in “Hitler’s Bomb” (2005), that German physicists conducted three nuclear tests in 1944 and 1945. But he gave no proof. A more widely accepted view is that Hitler’s program, which predated the Manhattan Project, faltered in midwar because of scientific errors and Norway’s successful saboteurs.

By 1942, the British knew that Germany had chosen heavy water, or deuterium oxide, to moderate atom-splitting chain reactions to produce bomb-grade plutonium. They knew further that the Norsk Hydro plant in Norway, which had been extracting heavy water since 1934 for making fertilizer, had been taken over by Nazi invaders as the world’s best source of the isotope for Berlin’s atomic weapons program.

A 35-man British commando team had been lost on a 1942 mission to sabotage the plant. Britain then enlisted the Norwegian volunteers under Mr. Ronneberg for Operation Gunnerside, endorsed by Prime Minister Winston Churchill. Air attacks were not ordered for fear of heavy casualties to Norwegian workers and a low probability of success because the heavy water had been distilled in a basement fortified against bombs.

After training in Britain, the group parachuted into Norway. A four-member advance team with a radio and supplies went first, in October 1942. Six others followed in February. They rendezvoused at a cabin 40 miles from the target, at Vemork, on the forested plateau called the Telemark, a national park today.

Blizzards stalled them for a week. Finally, they moved out. One man was designated to break off from the team to maintain radio contact with London. Nine others set off with rations for five days, explosives, fuses, Tommy guns, grenades, compasses and a pair of metal shears that Mr. Ronneberg had picked up at a London hardware store. That final item would prove critical.

They skied by night, rested by day and reached the gorge late on the night of Feb. 27, 1943. Steep slopes plunged 1,000 feet to the Mana River. The power plant was perched on a ledge halfway up the far slope. A guarded suspension bridge over the river led to the front entrance. At the back was a railway line and the German troops’ barracks. Guards patrolled the tracks and a wire fence around the back entrance.

There was no easy way in. “There were so many things that were just luck and chance,” Mr. Ronneberg told The Times. “There was no plan. We were just hoping for the best.” They decided to try the back way.

They waited for hours after midnight, watching the changes of night-shift workers and guards. Then, 75 yards upstream, they climbed down into the windswept gorge, clinging to shrubs and branches to break falls. They crossed the river on an ice bridge, then slogged up the far slope, waist-deep in snowdrifts. They saw guards on the suspension bridge, but the rushing river and the plant’s hum masked their own noises.

Creeping down the railway tracks unseen, they hid behind storage sheds near the perimeter fence. Five remained concealed there, ready to fire on the barracks or the guards, but they were not seen. When a sentry left the fence to make rounds, Mr. Ronneberg and three others dashed to the gate, cut a padlock with the shears and darted into the compound.

They split into two teams. All doors were locked, but Mr. Ronneberg and Fredrik Kayser found a small duct for cables and pipes. Mr. Ronneberg and Mr. Kayser squeezed in, dragging rucksacks of explosives behind them. The duct led to a cavernous hall.

They recognized it as the heavy-water production center: a latticework of iron pipes, rubber tubes, electrical wires and 18 stainless steel cylinders, each 50 inches tall and 10 inches in diameter — the heavy-water containers. There was no guard, only a workman at a desk. They dropped down, and Mr. Kayser put a gun to the man’s chest, urging him to be silent.

Mr. Ronneberg unpacked the rucksacks and began attaching explosives to the storage cylinders and water-distillation apparatus. They were joined by the other two demolition men, who had broken a window to get in. They set fuses on 30-second timers, ignited them with matches and fled.

As they raced past the barracks, they heard the muffled crump of the explosion. Soon sirens began to wail at the plant. But the saboteurs were out of sight by the time Germans scrambled from the barracks and workers scattered in chaos. A hunt by 2,800 soldiers spread over the countryside. But by sunrise, the saboteurs were well away, beginning a 280-mile trek across forests and mountains to neutral Sweden.

The raid — with no shots fired and no saboteurs wounded — had destroyed the cylinders, sending 1,100 pounds of heavy water down a drain, along with the plant’s capacity to make more. It took the Germans four months to rebuild, and more time to restore full production. But in November, the Vemork operation was crippled again by Allied bombers.

Hitler ordered the project moved to Germany, but a Norwegian ferry carrying the equipment and the remaining stocks of heavy water was sunk on route by resistance saboteurs in early 1944. That ended Nazi Germany’s struggle for Norwegian heavy water and all of the regime’s realistic hopes for an atomic bomb.

As time goes on, the members of the Greatest Generation around the world that were part of the resistance to Nazi tyranny have been leaving us, and Mr. Ronneberg’s passing is just one of those examples. While all of them gave the full measure of their service, few can say, as Ronneberg could, that what they did may very well have saved hundreds of thousands of lives at a crucial point in the war when the prospect of Nazi Germany being able to unlock the secrets of an atomic bomb were still very much on the table. Even if the mission had failed, it’s still possible that the Germans would have failed to achieve that breakthrough before it was too late, but this mission seems to have guaranteed that.

Congratulations on a job well done, sir.

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Doug Mataconis
About Doug Mataconis
Doug Mataconis held a B.A. in Political Science from Rutgers University and J.D. from George Mason University School of Law. He joined the staff of OTB in May 2010 and contributed a staggering 16,483 posts before his retirement in January 2020. He passed far too young in July 2021.


  1. JohnMcC says:

    The things my father’s cohort had to do in that war still bring tears to my eyes. I served in VietNam and when the occaisional ‘thanks for your service’ comes my way I always want to explain that I actually had it very soft and safe compared to millions of men in the previous generation.

    Salute! indeed.

  2. Franklin says:

    I had only vaguely heard about this mission before. It’s just incredible!

  3. Michael Reynolds says:

    What were we all doing at age 23? Not parachuting into Nazi-occupied territory and saving the world, that’s what.

  4. Electroman says:

    There’s no question that this fellow and his men were heroes in every way.

    That being said, the German atomic bomb project was crippled by their insistence that heavy water was involved at all. The Manhattan project used carbon instead of heavy water, and it worked. So the heavy water was actually never going to result in an actual bomb by the Germans – it was a scientific dead end.

  5. Kathy says:

    @Michael Reynolds:

    We owe people like Joachim Ronneberg the fact that we didn’t have to parachute into hostile territory. We didn’t have to save the world, only because he and his generation had already done so.

  6. JohnMcC says:

    @Electroman: I had read that the German ‘Manhattan Project’ started off with such a wrong assumption. Would be interested in the physics; is it possible that the ‘heavy water’ system would have led to fission weapons? Was the industrial base of Europe sufficient to build an equivalent weapon? I recall that the US A-Bomb project used an amazing percentage of the total US electrical production in ’44 and ’45 (I forget the percentage and don’t feel like googling it but TVA generating power was the reason Oak Ridge TN was invented). Of course, once the bomb went off, the process became widely understood and repeating the act was — not EASY but easier — so possibly less electrical power was needed the second time fission was ‘invented’ in Soviet Russia.

    Also I understand it’s true that the Nazi government did not place such priority on the Bomb being rather busy with other projects.

    Maybe the wrong forum to chat that stuff up but interesting to a few demented persons such as I.

  7. Electroman says:

    @JohnMcC: Nope, heavy water systems wouldn’t work in the 40s. Nuclear reactors have to be controlled, and they are controlled by carbon rods. The Germans measured the neutron capture cross-section of deuterium (the stuff that makes heavy water heavy) and thought it was much larger than it really is. Carbon actually has a large NCC, and that’s what makes current reactors work controllably. It ‘s definitely possible to build a heavy-water-based reactor today (CANDU is such a reactor), but there’s little need, as carbon is cheap and plentiful.

  8. Kathy says:


    Also I understand it’s true that the Nazi government did not place such priority on the Bomb being rather busy with other projects.

    Among other things, Germany in that period developed cruise missiles (V1), ballistic rockets (V2), fighter jets, and helicopters.

    The helicopters came to nothing, but the missiles and jet fighters were deployed. The fighters were misused in dog fights against other fighters, rather than as interceptors of heavy bombers; and few were produced (all those bombers dropping, you know, bombs, on all those factories and bridges and such).

    The V1 was a pulse-jet engine with a warhead. The V2 burned alcohol and oxygen in a rocket engine and carried a warhead as well. both had some primitive guidance system. I don’t recall how reliable they were, but they functioned as area weapons, causing more panic than damage. The V1 could be, and was, shot down by aircraft.

    There’s speculation, too, that Heisenberg, the most prominent physicist left in Germany (a lot of top scientists fled Europe for the US, and were the greatest asset in the Manhattan Project), may have purposefully obstructed the development of the nuclear bomb.

  9. JohnMcC says:

    Check and thank you!

  10. gVOR08 says:

    IIRC from reading Heisenberg’s War some years ago it was never clear whether Heisenberg didn’t want to develop a bomb, or just didn’t think it was technically and economically feasible for Germany to do it. But he seemed to be more interested in getting draft deferments for his staff than anything else. He had a famous, and somewhat mysterious, conversation with Niels Bohr in 1941 in which they may have discussed the morality of developing a bomb.

    Bohr was in Denmark in ’41. In ’43 he was spirited out of the country by the underground. There’s a story that he had squirreled away a few ounces of heavy water, which he hid in a beer bottle. He grabbed it on his way out, but discovered later it was the wrong bottle. He’d smuggled beer out of occupied Denmark.

  11. JohnMcC says:

    @gVOR08: But of course the image of the ‘absent minded professor’ is totally fiction.