Water was dripping in a hydrogen plant at Rjukan in Telemark, Southern Norway, as it had done since1934. But this was no ordinary water, and no ordinary plant - it was the only facility in Europe that produced heavy water in large-scale volumes.
The Germans kept the plant under heavy guard during World War II - for good reason. The barrels of heavy water that were rolled out were sent to Germany, where they were used to control nuclear fission.
Following the occupation of Norway in the spring of 1940, it soon became clear that the Germans were interested in heavy water. By the start of 1942, production at new installations in Rjukan, based on a German method, increased to 100 kilos per month. Not long after, the Germans announced they wanted to increase output further.
The situation escalated to the point that Hydro's top management protested and the company's managing director Bjarne Eriksen was arrested in early 1943 and sent to a concentration camp in Germany.
A secret weapon?
It was known in London and Washington that two German atomic physicists were working on nuclear fission, and it was assumed that heavy water had something to do with Hitler's threat of a secret weapon.
Norwegians in London assisted in the plans to sabotage the heavy water unit at the Vemork power plant at Rjukan, and photographs and sketches of the plant were sent to London by Norwegian contacts at the facility, in particular Jomar Brun, manager of the heavy water unit.
A huge political thriller began to unfold in 1943 and 1944. Was this a question of preventing the development of a nuclear weapon? Was this an arms race? In any case, the outcome could determine who won the war.
The first attempt to attack the Vemork plant ended in tragedy. Two planes from the 1st Airborne Division crashed in fog in Southern Norway, and all aboard were either killed in the crash or shot by the Germans. A sabotage operation was then planned. This was to be carried out by specially trained Norwegians.
A total of 12 hand-picked men were dropped by parachute onto the Hardangervidda mountain plateau, a good distance to the west of Rjukan and the Vemork plants. They stayed on the plateau, some 1,200 meters above sea level, throughout several winter months, eating the meat and stomach contents of wild reindeer.
The Vemork action is considered one of the most heroic sabotage acts of World War II. It was daring and spectacular in every way. Those who assigned the task were not at all sure that the men who carried it out would survive.
To reach the Vemork plant, the group of saboteurs had to cross the river right at the bottom of the gorge, as they could not use the suspension bridge. Joachim Rønneberg, the group leader, explains that all they had to go on was an aerial photo, taken at a height of 4,000 meters, that suggested that this was viable.
It was only after Claus Helberg had been out on a couple reconnaissance missions in the area that the group decided that the seemingly impossible task of climbing across the gorge could be attempted.
Through a minefield
One hour before midnight on February 27, the 12 saboteurs climbed down the gorge and across the ice-choked river, edged up the rock face on the other side, and emerged by the railway track to the hydrogen plant. The cover team now had to scramble up and cut through the gate or the railings.
Knut Haukelid and Arne Kjelstrup found the path alongside the railway line, but felt reasonably sure that mines had been laid to protect the facility from intruders. They cut the iron chain that blocked the way. Jens Anton Poulsson, who was the coordinating link with the men behind signalled the main group to proceed. They were soon all at the gate. And just minutes later, everyone was in position.
No lives lost
Entering the plant was just as challenging. Rønneberg, who led the explosives team, relates that the group first tried to get in through a basement door, without success. The brief from London had told them to climb a stairway to a hole in the wall for the cable, and to follow the cable tunnel running below the ceiling of the ground floor of the plant.
Rønneberg and Hans Storhaug made it in this way and took the guard by surprise. Birger Strømshaug, Fredrik Kayser and Kaspar Idland broke a window to get in, but the German guards heard nothing above the powerful drone of the generators.
"Two of us mounted the explosive charges. The fuses were about two minutes long. I cut them down to 30 seconds and lit them," says Rønneberg.
"How did you get out so fast?"
"I had a key. We knew that our cover squad was in position. The German guards had been put out of action, locked up in the guardhouse," he explains.
The charges blew, the sound of shattering glass again split the air, but the German guards can hardly have grasped that it was an explosion. A guard sauntered out, tried the door to the electrolysis facility, found it locked, and went back inside the guardhouse. A short time later, he came out again with a torch and shined it along the ground. The Germans must have thought the snow had triggered one of the mines to explode. The guard gave up and went back into the guardhouse again - and probably saved his life.
By the time the Germans had realized what had happened and soldiers started streaming up to the Vemork plant, the saboteurs were already far down the railway line on their way to Rjukan. It was very dark and the snow was deep but they all got away.
Once back on the mountain plateau, the group split up. The explosives team travelled by ski, fully armed and in uniform, over the high country and across the valleys of Eastern Norway to Sweden. The others spread out over the plateau. The Germans brought in thousands of soldiers and organized an extensive search, but were unable to find any of the saboteurs.
The successful action destroyed the facility and large quantities of heavy water.
Many killed in bomb raid
The heavy water plant was rebuilt and production restarted during the next six months. On the night of 16 November 1943, 140 US bombers swooped in over Rjukan and totally destroyed the Vemork power station and electrolysis plant. Many people were killed. After that, the Germans gave up producing heavy water at Vemork.
"Hydro" sinks to bottom of the Tinnsjø lake
A couple of months later, the saboteurs discovered that the Germans planned to ship all the semi-finished products from Vemork to research centres in Germany. Orders came by radio from London to destroy the cargo during transport. The weakest link was the journey by train ferry over the Tinnsjø lake. An explosion in the bow sank the "Hydro" on 20 February 1944, and ended the last chapter in the story of heavy water in Norway. The sinking of the "Hydro" cost four Germans and 14 Norwegians their lives.
The heavy water cargo was closely guarded at all times, but the boat that was to transport the shipment stood unwatched the night before. One of the three saboteurs had experimented with a timer and detonating mechanism, and he tried to set the explosion to go off when it would be easiest to rescue passengers.
The ferry's departure was unfortunately delayed. However, far more lives would have been lost if the explosion had been set off on a weekday. There was never many passengers on Sundays.
Fifty years later, to the day, on Sunday 20 February 1994, the county governor of Telemark unveiled a memorial in honor of the victims, close to the place the "Hydro" sank.
"Not so heroic"
Later the saboteurs played down the significance of their own role in the action.
"We were sent back to Norway from England as the King's men. We were armed and could hide in the mountains if we were discovered. It was worse for the people in Rjukan who helped us. They had families and homes and farms to take care of. They and their families had to live in fear of what could happen if they were found out," commented Knut Haukelid, who returned to Rjukan many years later for a reunion with the men who carried out the Vemork action.