As quickly as the storm swept into the Vidda, it blew itself out. On February 22, the six Gunnerside men woke up to silence. They stepped from the cabin into a clear, windless day. The blizzard had transformed the landscape into high drifts and flat, indistinct planes of snow. Stalagmites of ice and snow stood like quiet sentries.

Rønneberg gave the order that they must depart for Fetter by early afternoon. For six days, they had been out of contact, and, as far as Tronstad or Grouse knew, they might be dead and the operation off. They must hurry.

They returned to the general area of their depot and marched about the drifts of snow until they found one of the rods marking its position. They retrieved some extra rations, but given the distance and steep terrain they had to travel to reach Lake Store Saure, Rønneberg decided to minimize their loads. They would only carry explosives, uniforms for Grouse, rations for ten men for five days, and their operational equipment: weapons, hand grenades, shears, axes, field glasses, detonators, time fuses, and first-aid equipment.

At 1 P.M., the team was back at the cabin, ready to head out, when Haukelid spotted a man towing a sled. He was heading straight toward them. There was no doubt that he had seen their ski tracks and was coming to investigate. When the man was a few steps from the door, they sprang out. With six gun barrels pointed at him, his weathered face paled.

“What are you doing in the mountains?” Rønneberg asked.

“I’m a hunter,” he said, innocently enough.

They searched him and his equipment. His identity card stated he was Kristian Kristiansen, forty-eight, from a valley due east on the edge of the Vidda. On his sled was over fifty pounds of reindeer meat. He was carrying rifles and several thousand kroner, and his pocketbook contained a list of names and addresses in Oslo. He was clearly who he said he was, the list clients for the meat. That did not mean that he was not a threat, particularly when he gave contradictory statements on his feelings about the Nazi occupation.

From the looks of the others, Haukelid knew they were thinking they might need to kill him. If they let him go, he might reveal their presence to the Germans or the police. He was in all likelihood harmless, but they could not be sure. Rønneberg needed to decide what to do.

Idland asked to speak with their leader outside the cabin. They came out into the bright day. “I’ll shoot him for you,” Idland said. Rønneberg knew Idland was trying to relieve him of the responsibility. It was a kindness. He tried to put himself into Kristiansen’s shoes. He might not pose a threat. Rønneberg’s instructions were that if the unforeseen occurred, he must act with the mission foremost in mind. Finally, Rønneberg said to Idland, “We’d better take him with us for now.”

Kristiansen immediately proved useful. They cooked some of his reindeer meat, saving their own rations. Then Rønneberg asked if he could guide them to Lake Store Saure. He agreed. They decided to leave that night to avoid any further chance encounters. When they departed at 11 P.M., Kristiansen was in the lead, a sled tied to his waist loaded with rations and the uniforms. Rønneberg stayed close behind, compass in hand, to ensure they were following a proper course.

The hunter proved a fine guide. Not only was his path sure, but he skied a course that used the natural contours of the land, economizing effort. It was, Rønneberg thought, beautiful to watch.

At dawn, February 23, the sun rose, first bronze, then gold, over the mountains. Kristiansen chatted easily with them now and even attempted to buy one of their Tommy guns. When they came across a herd of reindeer, Kristiansen asked to be allowed to shoot some of them, to be collected later. Rønneberg refused, but he was coming to the conclusion that their captive was a simple mountain man and not a threat.

Seven miles from Fetter, they spotted a man crossing the lake below. They dropped quickly behind some boulders. Rønneberg waved Haukelid over and handed him a pair of field glasses. Given that the skier was headed toward Bjørnesfjorden, he might well be a member of Grouse out searching for them. Haukelid would know better than anyone if it was indeed one of them.

Although the skier was only a few hundred yards away, Haukelid could not make out who it was. He had a heavy beard and was bundled up in thick layers of clothes. Then he sighted another skier coming around a bend, a hundred yards behind the first. Haukelid made his way quickly along a ridge to get a closer look.

The two skiers came up from the valley toward Haukelid. Near the crest, they stopped. One, then the other, scanned the surrounding area. They were looking for somebody, for something. As one of them turned, Haukelid recognized a weather-beaten Helberg. Beside him, in an unkempt red beard, was Kjelstrup. For a second, Haukelid remained hidden, overjoyed at the sight of his friends. He wanted to say something funny, but seeing how thin and wan they looked, he thought better of it. Instead, he simply coughed, and the two swung their heads around, startled, hands on guns. When they recognized Haukelid, a shout, a whoop, then a holler rose over the valley.

Poulsson had sent Helberg and Kjelstrup out to search for Gunnerside. By pure luck, their paths had crossed.

The men decided to release Kristiansen with a warning that if he spoke to anybody about them, they would make it known that he had helped guide their party. “Stay on the Vidda and say nothing,” he was told. Nobody felt completely at ease with the situation, but it was a risk they measured in favor of taking an innocent life.

Helberg went ahead to Fetter before the others to warn Skinnarland so that he could get away before being seen. His identity had to be kept secret even from Gunnerside in case anyone was captured during the operation.

Crowded into Fetter that night, February 23, the men had a feast. Gunnerside provided biscuits, chocolates, powdered milk, raisins, and, most welcome to Poulsson, tobacco. Grouse offered reindeer meat of every sort, including marrow, eyeballs, stomach, and brain. Their guests were happy to stick with plain meat.

After a night’s rest — every bed and inch of floor taken over by curled-up, sleeping figures — the ten men had some coffee and a breakfast of reindeer, boiled or roasted. Then they gathered to hash out their operational plan. First, Rønneberg assigned each man his task. He would lead the demolition party, accompanied by Kayser, Strømsheim, and Idland. They would split into pairs to double their chances of reaching the target. Haukelid would command the covering party, which would be composed of himself, Poulsson, Helberg, Kjelstrup, and Storhaug. They would see that nobody interfered with the setting of the explosives. Haugland would go to Jansbu, the cabin beside Lake Skrykken. With his radio equipment, he would establish and maintain contact with London. Skinnarland (who was only ever referred to as their “local contact” in front of Gunnerside) would join him there.

Now they needed to figure out the best way in and out of Vemork. Pencil and paper in hand, Rønneberg sketched out the plant and surrounding area. He had never actually been there, but he knew every detail from their prep work and drew it true to scale. Rjukan to the right. Vemork in the middle. Lake Møs to the left.

The Vestfjord Valley split the rudimentary map from left to right, following the course of the Måna River. Vemork was perched on a ledge of rock above the river gorge, on the south side of the valley. The pipelines that fed its turbine generators rose above the power station along the valley wall. A single-track railway line curled east to Rjukan along this same wall. A seventy-five-foot-long, single-lane suspension bridge connected Vemork to the valley’s north side. Located in the hills by the bridge was Våer, a hamlet with a scattering of houses for the plant’s staff, through which the road between Lake Møs and Rjukan ran. A long, high trek up the valley’s northern wall led to the endless Vidda.

They debated three main routes. They could approach across the top of the southern side of the valley and descend to the plant alongside the pipelines. This idea was quickly dismissed, because a guard had recently been placed at the top of the pipes, and numerous minefields lined this approach. They could make a straightforward attack: ski down to Våer, neutralize the guards on the bridge, and head across to the plant. This had the advantages of being fast and easy, but if the guards were able to raise the alarm, the team would have to make their attempt on the heavy-water cells in the middle of a firefight. Any escape would be doubtful. Last, they could cross down through the gorge, climb up to the railway tracks, and enter the plant through a gate that was patrolled but not permanently guarded. This was their best chance of reaching the compound unseen, but at certain places along the railway line, there was a 600-foot drop straight into the river below. Rønneberg decided not to make a decision until they had secured a new update on the plant’s patrols and defenses.

After a trip into Rjukan to gather the latest intelligence from his old friend, Rolf Sørlie, Helberg waited for the others at a cabin in Fjøsbudalen, high up in an isolated side valley. From its vantage point, one could see Rjukan in the far distance. Vemork was two miles away on the opposite side of Vestfjord and was not visible. On Friday, February 26, the others joined him there. Helberg recounted what he had learned from Sørlie, and the nine men reviewed their potential plans again.

The gorge was unguarded and the entrance to the railway line only lightly patrolled, but, Helberg explained, this did not make this approach a better option. The climb from the gorge to the railway was all but impossible in summertime. With added ice and darkness, it was surely madness. Idland urged them to choose the bridge. It was swift and sure. They would kill the guards, then run up to the plant. Poulsson and Helberg doubted it would be so easy, but they agreed that the bridge was the better of the two approaches. Rønneberg sided with them. Only Haukelid insisted they should attempt the gorge. Otherwise, he said, they would likely face a pitched battle to reach the high-concentration plant.

From his backpack, Rønneberg produced a set of aerial photographs of Vemork, taken the previous summer. He had studied these in detail with Tronstad in Britain. Haukelid pointed to some scrub and trees rising along the sides of the gorge. “If trees are growing,” he said, “you can always find a way.” The others nodded. Rønneberg instructed Helberg to return the next morning to scout a potential route that would not have them plunging to their deaths.

An hour after sunrise, Helberg journeyed down toward Vemork, wearing civilian clothes. Because it was the weekend, he would blend in with others skiing in the populated valley. Passing Våer, which lay straight across the gorge from Vemork, he continued east through the woods above the road and along the northern wall of the valley. There he came upon a power-line track that ran parallel to the road. At last, he sighted what might serve as a path. Stashing his skis and poles, he made his way down into the gorge. Eventually, with the aid of some juniper bushes and pine branches, he reached the Måna River. Its surface was frozen, but the ice was very thin in places. In a warm spell, the river would prove impassable.

He hiked back and forth along the river’s edge, trying to spy a manageable route up the gorge to the railway line, which ran along a ledge cut into Vestfjord’s southern wall. Finally, he spotted a groove in the cliff that was somewhat less steep than the surrounding wall. Some bushes and small trees rose out of the splintered crevices of rock, and they could provide hand- and footholds for climbing. Weather and luck permitting, he figured it was possible.

Smiling broadly, he returned to the Fjøsbudalen cabin after lunchtime to give his report. Overwhelmingly, the team agreed with the proposal to climb up the gorge on the night of the operation. It would not be easy, but this route would give them a far better chance of sneaking into the plant, blowing up the heavy-water cells, and getting out before the guards were alerted. Rønneberg assented. The plan was set.