Norwegian heavy water sabotage

The Norwegian heavy water sabotage (Bokmål: Tungtvannsaksjonen; Nynorsk: Tungtvassaksjonen) was a series of Allied-led efforts to halt Nazi German heavy water (deuterium) production via hydroelectric plants in German-occupied Norway during World War II, involving both Norwegian commandos and Allied bombing raids. During the war, the Allies sought to inhibit the German development of nuclear weapons with the removal of heavy water and the destruction of heavy-water production plants. The Norwegian heavy water sabotage was aimed at the 60 MW Vemork power station at the Rjukan waterfall in Telemark.

The hydroelectric power plant at Vemork was built in 1934. It was the world's first site to mass-produce heavy water (as a byproduct of nitrogen fixing), with a capacity of 1.2 tonnes per year. Before the German invasion of Norway on 9 April 1940, the French Deuxième Bureau removed 185 kilograms (408 lb) of heavy water from the Vemork plant in then-neutral Norway. The plant's managing director agreed to lend France the heavy water for the duration of the war. The French transported it secretly to Oslo, then to Perth, Scotland, and then to France. The plant was still capable of producing heavy water, however, and the Allies were concerned that the Germans would use the facility to produce more.

Between 1940 and 1944, a series of sabotage actions by the Norwegian resistance movement and Allied bombing ensured the destruction of the plant and the loss of its heavy water.