During World War II, heavy water was considered indispensable as an aid to the production of atomic bombs. The only plant in the world where heavy water was produced continuously was the Norsk Hydro plant at Vemork, Norway. The Allies, thanks to a letter from Niels Bohr, knew that German scientists were working on an atomic bomb and high priority was given to the destruction of this plant. But the plant was situated deep within an icy gorge and just four months earlier Operation Freshman ended in disaster when two gliders carrying 34 British commandos crashed before they reached the factory.
The Germans needed only five tons of heavy water to build a bomb, so in February of 1943 nine Norwegian commandoes were sent to destroy the plant. Months before the raid, four men were parachuted into the forest near the plant. Codenamed “Grouse”, their job was to prepare for the sabotage and to radio England with news of the facility. They had to spend the winter hiding in the harsh wilderness of the Hardangervidda mountain plain, eking out what was left of their rations with wild reindeer. They even ate the contents of the reindeer’s stomach to get vitamins.
On February 16, 1943 the Norwegian commandos, codenamed “Gunnerside”, landed on the mountain plain 50 km from their intended destination and straight into a blizzard. They walked for days until they reached the “Grouse” group. On the evening of February 27, the men descended into the gorge and used wire clippers to cut the security fence. “Grouse” took up covering positions while “Gunnerside” placed explosive charges on the heavy water containers. The German guards, thinking they were safe within their frozen cavern, never noticed a thing. The commandos escaped without a shot being fired. They eventually split up into two groups, one skiing across Norway into the safety of Sweden, the other hiding out in the wilderness and maintaining radio contact with London until the end of the war. None were ever captured.
The Germans were quickly able to rebuild the plant. Deciding that another manned mission was too dangerous, the Americans sent 140 B-17’s on a bombing raid and destroyed the factory. But a significant amount of heavy water still remained in German hands, and was being readied for transport back to the Fatherland. The night before the ferry carrying the water was to set sail, saboteurs managed to place a timed charge on board. On Sunday, February 20, 1944, halfway through the trip, there was an explosion and the ferry sank within minutes, taking the vital heavy water down with it to rest at a depth of 460 meters. The German heavy water threat was finally extinguished.
The events surrounding Operation Gunnerside were turned into the 1965 movie The Heroes of Telemark starring Kirk Douglas.