Birger Stromsheim - Telegraph Once again, however, appalling weather intervened, and they landed 18 miles away from the drop zone. Stromsheim and his colleagues were forced to spend five days struggling through snowstorms and freezing temperatures on langlauf skis before finally meeting up with their compatriots. Together they set off for Vemork at 8pm on February 27. The plant, perched at the top of a thickly-forested ravine, appeared impregnable, with Germans guarding the bridge that led to its entrance. The commandos, however, decided to climb down one side of the ravine, cross the icy River Maan at its base, and climb up the other side, following a railway track that led into the plant. Arriving at the top of the ravine, a radio operator (Knut Haugland, who later took part in Thor Heyerdahl's Kon-Tiki expedition) was left behind to report if anything went wrong, while the other nine abandoned their skis and began the perilous descent, frequently sinking up to their waists in the snow. It was close to midnight before they managed to get to the other side, tired and soaked to the skin. Leaving another Gunnerside member, Hans Storhaug, with his Tommy-gun trained on the Germans guarding the bridge, the other eight began their assault on the plant. At exactly 30 minutes past midnight, one member of the party ran forward with bolt-cutters to force open the gate while Stromsheim and the six remaining saboteurs held back and provided cover. Once the gate was opened, a covering party took up firing positions inside the plant while Stromsheim and the three other explosives experts headed through another gate to the basement door, behind which lay the electrolysis chambers that produced the crucial heavy water. This door was supposed to have been left open by a Norwegian mole who worked in the plant - but he had been too ill to go to work that day. Confronted by this unexpected barrier, the explosives team split into two pairs to look for other ways in. Ronneberg and Fredrik Kayser found an entrance through a cable duct, crawling in to surprise a Norwegian caretaker, whom they held at gunpoint while they began to lay their charges. Meanwhile, Stromsheim and Kasper Idland had found a window at the back of the basement. Unaware that Ronneberg and Kayser were already in, Stromsheim decided they had no choice but to risk alerting the Germans by smashing their way through. Ronneberg had laid half the necessary charges when he heard the sound of breaking glass. Kayser swung round with his Tommy-gun ready to fire before realising the noise came from their fellow saboteurs. Stromsheim helped place the remaining charges while Ronneberg laid the fuses. Though they had initially planned to give themselves two minutes to get away, the risk of the German guards arriving was such that they instead placed 30-second Bickford fuses, despite knowing that this would not give them enough time to get clear of the plant before the explosion. The tension was heightened further when, just as the fuses were being set, the caretaker announced that he had misplaced his glasses and refused to leave without them. Though desperate to make their escape, the commandos proceeded to spend precious moments in the search for the spectacles - which were soon located. The foolhardiness of this benevolence was demonstrated when they heard footsteps approaching - but fortunately it was another Norwegian civilian, who was ordered to put his hands above his head while the fuses were lit. Kayser counted to 10 and then told the two civilians to run for their lives, while the raiders rushed out into the night. In the event they need not have worried. There was only a dull thud as the charges went off, too muffled to alert the guards, but it sent around 1000lbs of heavy water across the floor and down the drains, . "The explosion itself was not very loud," recalled one of Stromsheim's colleagues. It sounded like two or three cars crashing in Piccadilly Circus. By the time the guards discovered what had happened, the Gunnerside team were already back across the gorge. Stromsheim, Ronneberg, Idland, Storhaug and Kayser then headed back into the snowstorms on a 250-mile cross-country ski to the safety of neutral Sweden. Back in Britain, SOE chiefs would later deem Operation Gunnerside the most successful act of sabotage of the Second World War. For his part, Stromsheim was described in his military file by Ronneberg as "beyond doubt the best member of the party." Birger Edvin Martin Stromsheim was born in the central Norwegian port of Aalesund on October 11 1911 and worked as a building contractor before the war. He spent the early months of the German occupation building quarters for German soldiers but was determined to get to Britain to join the Special Operation Executive's team of Norwegian commandos. He and his wife Aase travelled by boat to the Shetlands in September 1941 and Birger Stromsheim was soon being trained at a succession of SOE bases in weapons" handling and street-fighting. The most important preparation he received was at Station XVII, the explosives-training base at Brickendonbury in Hertfordshire, where a full-scale model of the basement of the Norsk Hydro plant was built. For his part in the raid, Stromsheim was awarded the British Military Medal; the Norwegian St Olav Medal; the US Medal of Freedom; and the French Legion of Honour and Croix de Guerre. The success of Operation Gunnerside convinced the Nazis to relocate their heavy water project and move their remaining stores of potassium hydroxide, from which heavy water was distilled, away from Vemork. The chemical was loaded on a ferry, Hydro, but this was sunk by another Norwegian resistance operation, finally sealing the fate of Germany's atomic weapons programme. The events of the two operations were so daring that they was made into the film, The Heroes of Telemark (1965), starring Kirk Douglas and Richard Harris - though the participants were far from complimentary about Hollywood's attention to detail. Stromsheim subsequently took part in Operation Fieldfare, which in late 1943 and early 1944 sent him and other Norwegian commandos, including Ronneberg, back into Norway to disrupt German supply lines in the event of an Allied invasion. After the war, Stromsheim returned to building and was involved in preparations for Norwegian "stay-behind" units in the event of a Soviet invasion of his country. Birger Stromsheim's wife predeceased him. He is survived by a son and a daughter. Birger Stromsheim, born October 11 1911, died November 10 2012