The Norwegian resistance sabotage the Vemork Norsk Hydro plant in the town of Rjukan in the county of Telemark, Norway, which the Nazis are using to produce heavy water, which could be used in the manufacture of an atomic bomb.
Kirk Douglas plays Rolf Pedersen, a Norwegian physics professor, who, though originally content to wait out the war, is soon pulled into the struggle by local resistance leader Knut Straud (based on Knut Haukelid, portrayed by Richard Harris).
They are both smuggled to Britain to have microfilmed plans of the hydroelectric plant examined, and then return to Norway to plan a commando raid. When a force of Royal Engineers, who were to carry it out, are all killed, Pedersen and Straud lead a small force of saboteurs into the plant. The raid is successful, but the Germans quickly repair the equipment.
The Germans then plan to ship steel drums of heavy water to Germany. Pedersen and Straud sabotage a ferry carrying the drums, and it sinks in the deepest part of a fjord.
Besides this sequence, the raids (Operations Grouse, Freshman, and Gunnerside) and the final attack are depicted in location filming, in which snowy Norwegian locations serve as a backdrop for the plot.
Knut Haukelid wrote a memoir of the attack called Skis Against the Atom published in 1954. John Drummond wrote a novel based on the same story called But for These Men. Both books formed the basis of the screenplay.
The film was originally announced in 1963. It was made by Benton Film Productions, a company of director Anthony Mann and producer S. Benjamin Fisz. Financing came from America's Allied Artists and Britain's J Arthur Rank Productions.
SF Ammonia was used to represent SF Hydro in the final scene.
The movie was originally called The Unknown Battle and was to star Stephen Boyd and Elke Sommer and be written by Ben Barzman. Later Anthony Perkins was announced as star. Eventually Kirk Douglas signed as the lead. Cliff Robertson was mentioned as a possible co-star before Richard Harris came on board.
"I hear they are spending five million dollars, so it's got to be spectacular and that means more fiction and less fact," said Haukelid during filming.
It was amongst the 15 most popular films at the British box office in 1966.
Stephen Boyd later sued Mann for half a million dollars for dropping him from the film. "I missed out on four good roles and plenty of money when he signed me without financial backing and then dropped the project," said Boyd later. "He asked me again later but I'd made other commitments so Kirk Douglas and Richard Harris made it under another title."
Ray Mears made a documentary called The Real Heroes of Telemark. Despite mainly sticking to the factual evidence, some scenes in the documentary, like the film, were partly dramatised, focusing more on the survival skills involved in the operation.
The same story was also covered in the 1948 Franco-Norwegian film Kampen om tungtvannet (La bataille de l'eau lourde — "The battle for heavy water"). Quite faithful to the real events, it even had many of the original Norwegian commandos starring as themselves.
In 2015 the Norwegian Broadcasting Corporation showed a TV series called Kampen om tungtvannet (also known as The Heavy Water War or The Saboteurs) based on the events.
The Saboteur, Andrew Gross' latest book, is a fictionalized portrayal of events with Kurt Nordstrum portraying Kurt Haukelid.