Operation Gunnerside: The Sabotage of the Vemork Heavy Water Plant

Objective and Wartime Context

During the Second World War, the Allied powers became increasingly concerned with Nazi Germany’s efforts to develop nuclear weapons. Central to this research was the acquisition of heavy water (deuterium), which scientific experiments had indicated could be used to produce plutonium in nuclear reactors [3]. The primary source of heavy water in Europe was the 60 MW Vemork power station, a hydroelectric plant owned by Norsk Hydro located at the Rjukan waterfall in Telemark, Norway [2, 4].

Built in 1934, Vemork was the world’s first site capable of mass-producing heavy water as a byproduct of nitrogen fixing, with an initial capacity of 1.2 tonnes per year [4]. Shortly after the German invasion of Norway on April 9, 1940, the Nazis ordered production to increase fivefold, signaling their intent to utilize the material for their nuclear project [3]. The strategic importance of the site was such that the Allies initiated as many as four separate perilous military operations to halt production [3].

Planning and Personnel

By the spring of 1942, the risk of a German atomic bomb had become unacceptable to British intelligence [3]. Planning for a ground-based sabotage mission required precise coordination between Allied intelligence and Norwegian assets. In March 1942, 24-year-old sergeant Einar Skinnarland was deployed to Norway to establish contact with agents in the Rjukan area and serve as a vital communication link to London [3].

The mission, designated Operation Gunnerside, utilized a team of nine Norwegian commandos [2]. These operatives were tasked with infiltrating one of the most heavily defended industrial sites in occupied Europe. The plant was protected by minefields, guarded bridges, and the formidable natural geography of the Hardanger Plateau [1, 2].

Execution of the Sabotage

On the evening of February 27, 1943, the commandos executed their infiltration [2]. To avoid the closely guarded single-lane suspension bridge and the minefields covering the mountains above the plant, the team chose the most hazardous route: descending to the bottom of the valley across a half-frozen river and climbing a 500-foot-high cliff in the middle of a winter night [2].

Once inside the facility, the commandos successfully infiltrated the basement of the plant [2]. Their specific objective was to destroy the water pipes and electrolysis equipment used in the production of heavy water [2, 3]. The operation was carried out with precision, allowing the team to escape the plant without a direct clash with the German garrison during the sabotage itself.

Outcome and Strategic Significance

Operation Gunnerside succeeded in destroying the heavy water production cells, significantly hindering the German nuclear program [2]. The sabotage caused a major setback for researchers such as Werner Heisenberg and Kurt Diebner [2]. In response to the attack and the continued threat of sabotage, the German Wehrmacht blocked off the Hardanger Plateau from the spring of 1943 until the end of the war, declaring it a forbidden area and confiscating mountain cabins to prevent further Allied infiltration [1].

While the commandos did not fully grasp the scientific significance of their target at the time, the mission is now recognized as a critical blow to Hitler’s atomic ambitions [2]. The effort was part of a broader series of Allied actions, which included bombing raids and the earlier removal of 185 kilograms of heavy water by the French Deuxième Bureau before the German invasion [4].