The Vemork hydroelectric plant at Rjukan in the Telemark region of Norway was, in 1943, the only facility in the world producing heavy water — deuterium oxide — in sufficient quantities to matter to Germany's nuclear weapons research program. Werner Heisenberg, leading Germany's nuclear effort, needed heavy water as a moderator for his experimental reactor. Without Vemork, the German nuclear program faced a bottleneck that could not easily be solved.
The British Special Operations Executive understood this in 1942. The challenge: Vemork was one of the most heavily defended industrial targets in all of occupied Norway. It sat on the edge of a 600-foot gorge in a mountain wilderness that experienced temperatures of minus 40 Celsius in winter. The suspension bridge across the gorge was the only approach and was guarded continuously. The surrounding mountains were patrolled by German troops.
The Approach That Failed
A first attempt, in November 1942, used British gliders carrying a commando force of 34 men. Both gliders crash-landed due to equipment failure and weather. All surviving men were captured by the Germans and executed under Hitler's Kommando Order, which mandated the summary execution of all captured Allied commandos regardless of circumstances.
SOE sent a second plan.
The Six Men
The second operation assigned six Norwegian agents who had been trained in Britain to reach the target on skis — a method the British glider approach had abandoned as too slow. The six men were Joachim Rønneberg, Knut Haukelid, Fredrik Kayser, Hans Storhaug, Birger Strømsheim, and Kasper Idland. All were Norwegians who had escaped to Britain after the German occupation.
They parachuted into the mountains of the Hardangervidda plateau on February 16, 1943, in the middle of winter, days before the target date. They spent four days skiing in extreme cold to reach the vicinity of Vemork, linking up with a small advance team that had been in place since October.
The Approach No One Expected
The cable shaft had been identified by one advance team member who had worked at Vemork before the war. It was a utility cable carrying pipes along the cliff face of the gorge — too narrow for the Germans to have considered it a viable approach to the plant, and accordingly unguarded. The team squeezed through it in single file, in the dark, without noise, gaining access to the basement of the facility.
The basement held the heavy water concentration cells — the electrolytic chambers where ordinary water was separated into its heavy water fraction.
The team placed their charges, set the fuses, and retreated. They encountered one Norwegian civilian worker in the basement during the operation. He asked what they were going to do. They told him as much as they could and found his glasses, which had fallen on the floor, before leaving — a detail that has struck historians as perhaps the most precisely human moment in a precision operation.
The charges detonated at 1:00 a.m. on February 27, 1943. Approximately 500 kilograms of heavy water concentrate were destroyed. Not a single shot was fired during the operation. Not a single German soldier was killed. Not a single member of the team was captured.
The Escape
The team's escape route was 340 kilometers by ski to neutral Sweden. They made it in approximately two weeks. The operation's German commander reportedly paced his office for hours after the attack, reportedly saying: "I don't understand it. How did they get in?"
German investigators concluded, after examining the scene, that either the attackers had been incredibly skillful, incredibly lucky, or both. They were, in fact, incredibly skillful — and they had trained for this specific approach for months.
The Vemork plant was repaired and resumed production. Allied bombing strikes and a subsequent attack on the ferry transporting the remaining heavy water stocks eventually ended German heavy water production permanently. By then, the German nuclear program had fallen so far behind that the war ended before Germany came close to a bomb.
Sources & Further Reading
Joachim Rønneberg, testimony to IWM and Norwegian national archives; Neal Bascomb, "The Winter Fortress: The Epic Mission to Sabotage Hitler's Atomic Bomb" (Houghton Mifflin Harcourt, 2016); SOE War Diary, National Archives UK HS 2/185.
