The Norwegian heavy water sabotage (; ) was a series of Allied-led efforts to halt German heavy water production via hydroelectric plants in Nazi Germany-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 12 tonnes per year. Before the German invasion of Norway on 9 April 1940, the French Deuxième Bureau removed 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 heavy water. 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. These operations — code-named Grouse, Freshman, and Gunnerside — knocked the plant out of production in early 1943. In Operation Grouse, the British Special Operations Executive (SOE) successfully placed an advance team of four Norwegians on the Hardanger Plateau above the plant in October 1942. The unsuccessful Operation Freshman was mounted the following month by British paratroopers, who were to rendezvous with the Operation Grouse Norwegians and proceed to Vemork. This attempt failed when the military gliders (and one of their tugs, a Handley Page Halifax) crashed short of their destination. Except for the crew of one Halifax bomber, all the participants were killed in the crashes or captured, interrogated and executed by the Gestapo. In February 1943, a team of SOE-trained Norwegian commandos destroyed the production facility in Operation Gunnerside; this was followed by Allied bombing raids. The Germans ceased operations, and attempted to move the remaining heavy water to Germany. Norwegian resistance forces then sank the ferry carrying the heavy water, the , on Lake