Operaatio Grouselle.

Destruction of the Vemork plant was mounted by the Combined Operations command in November 1942. The plan consisted of two operations: the first would drop a number of Norwegian locals into the area as an advance force, and once they were in place a party of British engineers would be landed by military glider to attack the plant itself.

On 19 October 1942, a four-man team of Special Operations Executive (SOE)-trained Norwegian commandos parachuted into Norway. From their drop point in the wilderness they had to ski a long distance to the plant, so considerable time was given to complete this part of the mission, known as Operation Grouse. This plan, unlike prior failures, included the team's studying and memorising blueprints.

Once the Norwegian Grouse team managed to make contact with the British, the British were suspicious, as they had not heard from the SOE team for a long time: they had been dropped at the wrong place and had gone off course from there several times. The secret question took the form of: "What did you see in the early morning of (a day)?" The Grouse team replied: "Three pink elephants." The British were ecstatic at the success of the Norwegian team's insertion, and the next phase of operations commenced.

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Operaatio Grouse (pyy) oli liittoutuneiden sabotaasioperaatio natsi-Saksan ydinohjelman tuhoamiseksi Norjan Telemarkissa sijaitsevan Møsvatnjärven lähellä.

Ensimmäisessä operaatiossa 19. lokakuuta 1942 neljä brittiläistä Special Operations Executive -erikoisjoukkojen laskuvarjomiestä hyppäsi lentokoneesta Norjan yläpuolella ja hiihti koko yön raskasvesitehtaalle. 

He olivat opetelleet salaisen kysymyksen, jota käyttämällä he saisivat yhteyden oikeisiin ihmisiin Norjan vastarintaliikkeessä.
Kysymys kuului: ”Mitä näit tänä aamuna?” 
Oikea vastaus oli: ”Kolme vaaleanpunaista elefanttia
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On 19 November 1942, Operation Freshman followed with the planned glider-borne landing on frozen lake Møsvatn near the plant. Two Airspeed Horsa gliders, towed by Handley Page Halifax bombers, each glider carrying two pilots and 15 Royal Engineers of the 9th Field Company, 1st British Airborne Division, took off from RAF Skitten near Wick in Caithness. The towing of gliders had always been hazardous, but in this case it was made worse by the long flying distance to Norway and poor weather conditions which severely restricted visibility.
                   

                

One of the Halifax tugs crashed into a mountain, killing all seven aboard; its glider was able to cast off, but crashed nearby, resulting in several casualties. 

The other Halifax arrived at the area of the landing zone, but although the conditions had substantially improved it was impossible to locate the landing zone itself, owing to the failure of the link between the Eureka (ground) and Rebecca (aircraft) beacons. After much endeavour and with fuel running low, the Halifax pilot decided to abort the operation and return to base. 

Shortly afterwards, however, the tug and glider combination encountered heavy cloud and in the resulting turbulence the tow rope broke. 

The glider made a crash landing, not far from where the other glider had come down, similarly inflicting several deaths and injuries. The Norwegians were unable to reach the crash sites in time, and the survivors eventually came into the hands of the Gestapo, who tortured them during interrogation (not sparing the badly injured) and later had them executed under Adolf Hitler's Commando Order.
                    
The most important consequence of the unsuccessful raid was that the Germans were now alerted to a determined Allied interest in their heavy water production.
The Norwegian Grouse team thereafter had a long arduous wait in their mountain hideaway, subsisting on moss and lichen during the winter until, just before Christmas, a reindeer was encountered.