NEW YORK — 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.
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, Mr. 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 in Alesund, Norway, on Sunday at age 99, his daughter, Birte Ronneberg, said.
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.”
Mr. Ronneberg led other raids, attacking German supply lines and destroying a railway bridge with plastic explosives. He received Norway’s highest decoration for military gallantry, the War Cross with Sword, from King Haakon VII; the Distinguished Service Order from Britain; the Legion of Honor and Croix de Guerre from France; and the American Presidential Medal of Freedom With Silver Palm. (The latter was established by Harry Truman to honor civilians who aided the war effort; it was replaced in 1963 by the Presidential Medal of Freedom.)
Joachim Holmboe Ronneberg was born in Alesund, Norway, on Aug. 30, 1919, one of two sons of Alf Ronneberg and the former Anna Krag Sandberg. Joachim and his brother, Erling, who also became a wartime resistance fighter, attended schools in Alesund, on Norway’s northwest coast. At 21, he escaped to England. He was a good skier and enlisted in the Kompani Linge, the Norwegian-exile special forces.
In 1948, Mr. Ronneberg joined the NRK public broadcasting network in Norway. He became a journalist and program director and retired in 1988.
He married Liv Foldal, a crafts teacher, in 1949, and had three children: Jostein, Asa and Birte.
For years, Mr. Ronneberg lectured widely about Norway’s history and his wartime experiences. While “The Heroes of Telemark” was filmed on locations in Norway, he often scoffed at the liberties taken with the facts. “They took a true story and spun their own idea around it,” he told The Daily Telegraph of London in 2010. “It should never have been allowed.”
While long celebrated abroad, the exploits of Mr. Ronneberg and nine other Norwegians involved in thwarting the Nazi nuclear project became widely known in Norway only in 2015 when NRK ran “The Heavy Water War,” a six-episode miniseries that became a national sensation. The statue of Mr. Ronneberg in front of City Hall in Alesund, the town where he lived, was put up later that year to observe his 95th birthday.
Mr. Ronneberg applauded the television series for introducing younger Norwegians to wartime history they knew little about, but he expressed annoyance that it had altered the names of the directors of Norsk Hydro, the company that ran the plant he blew up, who had collaborated with the Nazis. He told The Times that it was “quite incredible” that their real identities had been concealed and that painful memories of collaboration with the Nazis by Norway’s wartime leader Vidkun Quisling still hampered a clear and full historical reckoning.
“There is a lot of talk about ‘never again,’ but this is impossible if we don’t remember what happened back then,” Mr. Ronneberg said.
During preparations in England for the raid, the saboteurs had been promised a place in history by the mastermind of the operation, Leif Tronstad. “But none of the men were there for history,” Neal Bascomb said in perhaps the most definitive book on the raid, “The Winter Fortress: The Epic Mission to Sabotage Hitler’s Atomic Bomb” (2016).
“If you went to the heart of the question, none of them were there for heavy water, or for London,” Bascomb wrote. “They had seen their country invaded by the Germans, their friends killed and humiliated, their families starved, their rights curtailed. They were there for Norway, for the freedom of its lands and people from Nazi rule.”