Norwegian heavy water sabotage

The Norwegian heavy water sabotage was a series of Allied-led efforts to halt Nazi German heavy water 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, with a capacity of 1.2 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.
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 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 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 Norwegian commandos of SOE's Norwegian Independent Company 1 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 Tinn.

Background

and his colleagues studied the results of bombarding uranium with neutrons in 1934. That year, Ida Noddack first mentioned the concept of nuclear fission. In December 1938, four years after the Fermi publication, Lise Meitner and Otto Robert Frisch correctly interpreted Otto Hahn and Fritz Strassmann's radiochemical experimental results as evidence of nuclear fission.
News of the discovery spread quickly among physicists and it was realized that if chain reactions could be controlled, fission might be a new source of great power. What was needed was a substance which could moderate the energy of the secondary neutrons emitted by fission, so they could be captured by other fissile nuclei. Heavy water and graphite were the prime candidates for moderating neutron energy.
When Nazi Germany investigated the production of an atomic bomb, a range of options was identified. Although historical records provide limited detail on the German decision to pursue the heavy water approach, it became clear after the war that they had explored that option. Although ultimately unsuccessful, the approach chosen has been demonstrated as technically viable. Plutonium-239 makes effective weapons material, although it requires an implosion-type mechanism rather than the simpler gun-type trigger used in the Thin Man uranium bomb. Heavy water has been demonstrated as an effective moderator for ²³⁹Pu production, and may be separated from ordinary water by electrolysis. The German program had already been handicapped by the Nazi purging of German Jewish physicists and the conscription of others and ended in the autumn of 1942.

Approaches to developing a weapon

In nuclear-weapon development, the main problem is securing sufficient weapons-grade material; it is particularly difficult to acquire fissile isotopes of uranium-235 or ²³⁹Pu. Weapons-grade uranium requires mining, extracting and enriching natural ore. Plutonium can be "bred" in reactors fueled by unenriched uranium, which requires chemical separation of the ²³⁹Pu produced.

Plutonium production

Although the most common isotope of uranium, uranium-238, can be used as secondary fissile material in hydrogen bombs, it cannot be used as the primary fissile material for an atomic bomb. ²³⁸U can be used to produce ²³⁹Pu through the fission of ²³⁵U, which produces neutrons. The ²³⁹U will decay after a few days, turning into weapons-usable ²³⁹Pu.
The Germans found that a chain reaction could not be sustained if graphite was used as a moderator, and abandoned it. Unaware that this was due to impurities, they did not test ultra-pure graphite. Instead, they settled on a heavy-water-based reactor design. A heavy-water-moderated nuclear reactor could be used for nuclear-fission research and, ultimately, to breed the plutonium with which a bomb could be made.

Deuterium ("heavy water") production

In normal water, there is only one deuterium atom for every 6,400 hydrogen atoms; deuterium is more prevalent in the residue of water used as an electrolyte. An analysis of residues from the Vemork hydroelectric plant, a large-scale nitrate production plant using the Haber process, showed a hydrogen-to-deuterium ratio of 48. Norwegian Institute of Technology lecturer Leif Tronstad and Jomar Brun, head of the hydrogen plant, proposed a project in 1933. It was accepted by Norsk Hydro, and production began in 1935.
The technology is straightforward. Heavy water is separated from normal water by electrolysis, because the difference in mass between the two hydrogen isotopes translates into a slight difference in the speed at which the reaction proceeds. To produce pure heavy water by electrolysis requires a large cascade of electrolysis chambers, and consumes large amounts of electric power. Since excess power was available, heavy water could be purified from the existing electrolyte. Norsk Hydro became the heavy-water supplier for the world's scientific community, as a by-product of fertilizer production for which the ammonia was used. Hans Suess, a German adviser on the production of heavy water, had assessed the Vemork plant as incapable of producing militarily-useful quantities of heavy water in less than five years at its capacity at the time.

Operations to limit German access to heavy water

Pre-invasion efforts

French research considered the production of ²³⁹Pu using reactors moderated by heavy water and graphite. Preliminary French research indicated that the graphite then available commercially was not pure enough to serve the purpose, and heavy water would be required. The German research community had reached a similar conclusion, and had procured additional heavy water from Vemork in January 1940. The German firm IG Farben, a partial owner of Norsk Hydro, had ordered per month; Norsk Hydro's maximum production rate was then limited to per month.
The Deuxième Bureau directed three French agents to remove the world's extant supply,, of heavy water from the Vemork plant in then-neutral Norway in 1940. Norsk Hydro general director Axel Aubert agreed to lend the heavy water to France for the duration of the war, noting that if Germany won the war he would probably be shot. Transportation was difficult, since the Abwehr was present in Norway and had been alerted of ongoing French activities in Norway. If they had become aware of the shipment, they might have tried to intercept it. The French transported it secretly to Oslo, then to Perth, Scotland, and finally to France.
When France was invaded, French nuclear scientist Frédéric Joliot-Curie took charge of the material and hid it in a Banque de France vault and then in a prison. Joliot-Curie moved it to Bordeaux, where it, research papers and most of the scientists boarded the British tramp steamer .
The ship already had industrial diamonds, machinery and British evacuees aboard. The Broompark delivered its passengers and cargo, including the global stockpile of heavy water, to Falmouth, Cornwall on 21 June. The award of an OBE to Captain Paulsen was recorded in The London Gazette of 4 February 1941. Crucial to the success of the mission was the role played by Charles Howard, 20th Earl of Suffolk, the British liaison to the French scientific establishment.
Although the supply of heavy water had been removed, the plant was capable of producing more. The Norsk Hydro management's collaboration with the Germans was examined during investigations of collaborationism begun by Norwegian authorities after the war, but Aubert's cooperation with the French aided the company's case.

Operations Grouse and Freshman

In October 1942, Combined Operations Headquarters began operations to destroy the Vemork plant. There were two operations; the first would drop a number of Norwegians in the area as an advance force. When they were in place, a party of British engineers would be landed by military glider to attack the plant itself.
On 18 October 1942, a four-man team of Norwegian commandos of SOE's Kompani Linge parachuted into Norway. Since they had to ski a long distance to the plant from their drop point in the wilderness, considerable time was allotted for Operation Grouse. Unlike previous failed plans, Grouse required the team to memorize blueprints.
The British were suspicious, because the Norwegian Grouse team were delayed in contacting SOE team; the Norwegians had been dropped at the wrong place, however, and had gone off course several times. The secret question was, "What did you see in the early morning of ?" The Grouse team replied, "Three pink elephants." The British were ecstatic at the success of Grouse, and the next phase of the operations began.
On 19 November 1942, Operation Freshman followed with a planned glider-borne landing on the frozen lake Møsvatn near the plant. Two Airspeed Horsa gliders, towed by Handley Page Halifax bombers, took off from RAF Skitten near Wick, Caithness, Scotland. The towing of gliders, always hazardous, was worse in this case because of the long flight distance to Norway and poor visibility.
One of the Halifax tugs crashed into a mountain, killing all seven aboard; its glider cast off but crashed nearby, resulting in several casualties. Although the other Halifax arrived at the vicinity of the landing zone, the zone could not be precisely identified because the link between the Eureka and Rebecca radar beacons failed.
After many tries and with fuel running low, the Halifax pilot decided to abort the operation and return to base. Shortly afterward, the tug and glider experienced heavy turbulence and the tow rope broke. The glider crash-landed near the crash site of the other glider, killing and injuring several more people. The Norwegians were unable to reach the crash sites in time; the survivors were captured by the Gestapo, who tortured and later had them executed under Adolf Hitler's Commando Order.
The unsuccessful raid alerted the Germans to Allied interest in their heavy-water production. The surviving Norwegian Grouse team had a long wait in their mountain hideaway, subsisting on moss and lichen until they captured a reindeer just before Christmas.