Operation Gunnerside

16 February 1943

IT WAS 2320 when, in rapid succession, five British-trained Commandos leapt from a Halifax bomber over the frozen wilderness of the Hardanger Vidda in the Telemark region of central southern Norway. Jumping from just 700 feet, their chutes billowed open and floated in a neat diagonal line through the moonlight towards the vast white expanse stretching out to all horizons. Somewhere in that frozen wilderness were four comrades who, for three months, had battled starvation and some of the harshest conditions on the planet as they waited and waited and waited . . . Finally, the raid was on. The saboteurs knew from the huge risks they had been asked to take that their objective was of great importance – an impression underlined by their carefully worded orders. What they didn’t know was that Prime Minister Churchill in London and President Roosevelt in Washington were anxiously monitoring their mission. Operation GUNNERSIDE was one of the most important raids of the Second World War. It wasn’t until after the conflict that they learned quite how important.

At the outbreak of the war, Albert Einstein was one of a very small handful of people in the world who understood the terrible potential of atomic power. To most scientists, even very eminent ones, the notion that a single bomb could annihilate an entire city was absurd. Churchill was extremely sceptical too, but it wasn’t long before he was persuaded of the dire threat it posed. London, the intelligence suggested, was the first target on Hitler’s list. The reasoning was obvious: destroy the British capital and the war was won. Britain would surrender and the United States would be unable to help launch an invasion of Europe.

A great number of Germany’s leading physicists – many of them Jews – had fled the Nazis for Britain and the United States, bringing with them warnings of the rapid advances being made to build an atomic weapon. So began frantic efforts by the Allies to beat Germany to the bomb. In the US the atomic research programme was known as ‘The Manhattan Project’ and no expenses were spared in its development. To their advantage, the Americans did now have many of the world’s leading experts in their field, following their flight from the Nazis, but they were months off the pace, years even, and it was going to take a lot of time, effort and resources to overhaul their German counterparts. For fear of causing widespread panic, strict secrecy blanketed this apocalyptic arms race. No more than a few dozen scientists, military chiefs and senior politicians were aware of its existence.

German scientists had been working on three different approaches to developing nuclear energy. At the start of the war, the one considered most likely to succeed involved the production of a liquid known as deuterium oxide or ‘heavy water’. The fluid was used as a moderator to slow the nuclear chain reaction in unenriched uranium. This was a laborious, costly process and the entire world’s stocks of the fluid could be found in a few canisters inside a heavily protected hydroelectric plant known as Vemork in an ice-bound valley deep in the interior of Nazi-occupied Norway. But minute by minute, splash after splash, the stock of this potentially deadly liquid was increasing and Germany was inching that bit nearer to building the most powerful weapon in the history of warfare.

In May 1941, intelligence sources signalled that Germany had demanded a ten-times increase in Vemork’s heavy water production to 3,000 lb per year. By January 1942, production was ramped up to 10,000 lb per year. Churchill didn’t need the code-crackers at Bletchley Park to decipher the significance of the updates: Hitler was demanding rapid acceleration in the race to build the first atomic weapon. In June 1942, Churchill flew to New York to meet Roosevelt. Nuclear energy was high on the agenda of priority topics. The two leaders of the free world agreed that every effort should be made to thwart Germany’s bid to build the world’s first ‘super-explosive’. After the war, Churchill wrote: ‘We both felt painfully the dangers of doing nothing.’

Destroying the stocks of heavy water at Vemork was considered the most effective way of retarding Germany’s nuclear energy programme, but that was a great deal easier said than done.

An inside job was implausible. At that stage of the war, the Norwegian Resistance was no more than a fledgling operation with limited resources and very little offensive capability. There was also the problem of Vemork’s remote location. Roughly 150 miles from the coast, accessible only by one winding road, it sat on a steep, rocky slope of a narrow valley at the foot of the Hardanger Vidda, a beautiful but forbidding wilderness – the highest plateau in western Europe – where only the most experienced outdoorsman could survive for any significant length of time. The 3,500 square miles of terrain features barren, treeless, undulating moorland punctuated by hundreds of peaks, lakes, rivers, streams and marsh. In the summer, the Hardanger is a magnet for hillwalkers and nature lovers. In the winter, only the hardiest and most intrepid venture into its wind-blasted and frozen interior. When the Germans invaded Norway, they went around the Hardanger and they never advanced more than half a day’s march into it, for fear of being caught out by the volatile weather.

Bombing the plant was rejected on a number of grounds. Innocent lives were very likely to be lost and the hydroelectric plant, the principal centre of economic activity in the region, would be put out of action. What’s more, it was thought unlikely that an air raid would succeed in destroying the heavy water, which was stored under several storeys in the basement of the solidly constructed plant. But such was the urgency of the situation that there were even discussions about blowing the Møsvatn Dam at the head of the valley – a course of action that would have led to the deaths of hundreds, possibly thousands of civilians, with no cast-iron guarantee that the heavy water stocks would be put beyond use. After endless series of meetings and streams of interdepartment ‘Top Secret’ memos, the planners reached the conclusion that the only plausible option was a ‘coup de main’ raid carried out by elite Commandos in a joint mission involving the Special Operations Executive (SOE) and Combined Operations.

Established on Churchill’s order in the summer of 1940, SOE’s purpose was to wage guerrilla warfare behind enemy lines, to train and assist local resistance groups and carry out espionage and sabotage tasks – or, in Churchill’s words, the clandestine unit of highly trained irregulars was ‘to set Europe ablaze’. Many of the SOE operatives were refugees from the Nazi-occupied countries who, after completing their training, were reinserted into their homelands on specific missions. The work was amongst the most dangerous in the war.

In the early days, the organisation was not highly regarded within Whitehall. The ‘Ministry of Ungentlemanly Warfare’, as it was dubbed, was thought to cause more trouble than its achievements were worth. Existing intelligence and espionage services, local resistance groups and governments-in-exile all had cause to complain about its activities. When SOE was first approached about plans for an attack on the Vemork hydroelectric plant, it saw an opportunity to establish its credentials and silence its many critics.

The rough plan was for an advance party of SOE-trained Norwegians to be dropped by parachute onto the Hardanger. They would live in the wild and act as a reconnaissance unit and reception committee for a force of British glider-borne Commandos. Their task was to find a suitable dropping zone in the rugged terrain, guide in the aircraft, lead the British troops to the plant and help them escape. Airborne operations were best undertaken under cover of darkness, which ruled out any missions in the summer months when there was near-permanent daylight. During the summer of 1942, the instructors of SOE’s Norwegian unit were ordered to pick a handful of exceptional recruits with the aim of dropping them into Norway as soon as the RAF considered the nights long enough for them to operate in relative safety.

Operation GROUSE was the name given to the advance party and it was to be led by Jens Anton Poulsson, a pipe-smoking, Norwegian Army cadet and expert mountaineer who grew up in the town of Rjukan, a mile or so from the Vemork plant. The three men he put forward to make up the team, Claus Helberg, Knut Haugland and Arne Kjelstrup, were also born in Rjukan. Helberg, a brilliant skier and man of adventure, had sat next to Poulsson in school. The families still lived there but their sons were under strict instructions not to make contact with them. Haugland, one of the best underground W/T operators of the war, had worked with the embryonic Norwegian Resistance but escaped to Britain after being arrested on several occasions. Kjelstrup, a plumber, was born in Rjukan but raised in the suburbs of Oslo. Short and powerful, he had shown during Germany’s Blitzkrieg invasion that he was not a man to shy away from a fight, even in the face of overwhelming odds. The four men would set up an operating base in one of the small wooden huts dotted over the Hardanger used by walkers, hunters, fishermen and skiers.

The men were SOE recruits of the Norwegian Independent Company who had passed through a number of top-secret Special Training Schools (STS) across Britain, learning the dark arts of irregular warfare. (The unit was also known as the Linge Company after Martin Linge, the Commando leader killed in Operation Archery.) By the time they had completed the intensive and gruelling series of courses, they had become masters in close combat, demolition and sabotage, silent killing, wireless operation, intelligence gathering, propaganda and training local resistance militia. At the Norwegians’ main base in the Highlands of Scotland, the men underwent training in outdoor survival in extreme conditions . . . but their instructors soon realised that there was not a great deal they could teach the Norsemen. The great majority of them were first-class outdoorsmen who since childhood had learned how to survive in the most exacting conditions nature can present.

Surviving in the wild was one challenge, but overcoming German defences and destroying the heavy water supplies was quite another. Einar Skinnarland, SOE’s agent in the Rjukan area with contacts inside Vemork, had cabled London to report that there were 20 German soldiers stationed at Vemork, 35 billeted in a nearby school, 100 more a ten-minute drive down the road at Rjukan and a further 20 in billets near his family home at the Møsvatn Dam at the head of the narrow, winding valley.

Skinnarland was told he would learn of GROUSE’s arrival through a concealed message on the BBC Norwegian Service on the night they were to be dropped in. The announcer would say ‘This is the latest news from London’ rather than the customary ‘This is the news from London.’

By the end of the summer, the GROUSE party were put on standby to depart. They had completed the advanced courses of the SOE training, received their orders and reached a peak of physical fitness. Having packed and repacked their equipment over and over, they waited to be summoned to Wick Airfield. As always in parachute operations, they were at the mercy of the weather. If it was too cloudy or windy, the RAF couldn’t drop them. On two separate occasions in a month, they pulled on their parachutes and boarded the aircraft, the adrenalin pumping hard as they flew over the coast of their homeland and stood over the hatch in the floor poised to leap, only to be told the drop had been cancelled. On the first occasion, thick cloud meant that they were unable to locate the drop zone; on the second, engine trouble and heavy anti-aircraft fire over the coast combined to thwart them. The intense frustration felt by the four men is evident from Poulsson’s blunt comments in his operational notes.

A third attempt was made at nightfall on 10 October 1942. Once again, the four young Norwegians stood in line as the RAF dispatcher pulled open the hatch and the freezing wind rushed through the floor. Below, the snowbound plateau glistened under the bright moon. At 2318, the dispatcher hurled out half a dozen containers of supplies and equipment. There was no turning back this time. The young Norwegians were going home. Poulsson was the first to leap, followed barely a heartbeat later by Haugland, Kjelstrup and Helberg. Moving at 200 miles an hour, it was important not to hesitate; a few seconds delay could mean separation from the rest of the group by hundreds of yards. The dispatcher tossed out the final two containers and slammed shut the hatch. The rear-gunner counted the silk chutes drifting in perfect symmetry towards the frozen landscape.

The four men suffered heavy landings on very rough terrain. The RAF had dropped them in the wrong place, ten miles from the prearranged landing zone. ‘It was fortunate that none of us was severely hurt when we landed,’ Poulsson recorded in his log. ‘The ground was just a mass of stones.’ The four immediately tore off their parachutes for fear that a strong rush of wind would drag them over the rocky, broken land. The wind had scattered the eight containers over a very wide area and after four hours of searching they decided to start again the following morning. Had they been able to find the container with their skis and poles, they would have completed the search in a matter of minutes, but wading through heavy, wet snow in the dark they made little progress. They passed the rest of the night in sleeping bags, sheltered from the biting wind in the lee of a large outcrop of rocks. At first light, they resumed the search for the remaining containers, but without success. The rocky, hilly terrain and deep snow combined to frustrate the men for two full days. By the time they found the container with the skis, they were completely shattered.

The mountainside on which they had been mistakenly dropped lay ten miles to the west of where they wanted to be and roughly twenty miles from Vemork. Poulsson chose to head for a hut known as Sandvatn at Grasfjell, which he knew from his childhood and was situated in an ideal location. It was three miles from the designated landing zone for the gliders bringing in the Commandos and its remoteness made it highly unlikely that German patrols would discover them. What’s more, the area around it was largely flat, making it excellent country for wireless communication.

Ordinarily, a ten-mile cross-country journey was a distance that expert skiers could take in their stride, but the GROUSE team were burdened by equipment weighing a third of a ton, including food provisions to last a month, bulky radio equipment, clothing, spare ski equipment, first-aid materials, weaponry and ammunition. Poulsson decided to take all their rations but bury roughly 150 pounds of the nonessentials to collect after the raid. The difficulties of the march were compounded by damage sustained to their Primus stove during the parachute drop. Heat for cooking and drying out clothes was essential in Arctic-type conditions and, without any available, the party were forced to drop their plan of walking in a roughly straight line over the mountains. Instead, they would stay lower down, close to the lakes, where there were a number of huts they could use.

The weather had been kind to them but the day after they finally set out for Sandvatn, 21 October, a savage snowstorm burst over the Hardanger. Unable to find a hut, they spent the first night in snowholes, but the storm continued to rage the following day. Even without equipment the march would have been a slog, but with 500 pounds of kit it was a back-breaking experience. Dividing their kit into eight loads of thirty kilos, the four men made the same journey twice a day to bring up all the equipment to the next overnight location, skiing through deep, wet snow. Whenever they veered from their tracks, they sank up to their waists and soaked their clothing. Long-distance Nordic skiing is an exhausting business in any event, but in the teeth of a powerful storm, pushing through wet snow and blizzard conditions when already exhausted, it pushes men to the limits of their endurance. It is little wonder that the Norwegian explorer Roald Amundsen and his fellow adventurers trained on Hardanger. The temperatures, which can sink below minus 30 Celsius, coupled with the raging winds, were ideal preparation for polar expeditions – and even Amundsen experienced problems there.

GROUSE’s route was elongated further because the lakes and rivers were too treacherous to cross. The early winter ice hadn’t hardened sufficiently and so they had no choice but to march round them. Their rations were nowhere near adequate to give their bodies the energy required to cope with the combination of cold and physical exertion. Each man’s daily quota consisted of a quarter of a slab of pemmican (dried meat mixed with fat and fruits), half a cup of groats, a few biscuits, a handful of flour, small quantities of butter, sugar and chocolate. No one complained, however. Quoting an old Norwegian saying, Poulsson wrote in his log: ‘A man who is a man goes on till he can do no more, and then he goes twice as far.’ On some days, the storm was so fierce that they could advance no more than a mile or two. Poulsson’s predicament was made worse when he broke one of his ski sticks and found he had left his map behind. Their only respite was provided by the warmth and shelter of the huts they found.

Back in London, the SOE planners, having heard nothing from Skinnarland or Haugland, had begun to fear the worst when finally, fifteen days after they had set out from the drop zone, the shattered advance party finally arrived at the Sandvatn hut.

‘In good weather it would have taken us a couple of days but because the snow was wet, the ground wasn’t frozen, the streams and lakes were open (free of ice), it took us one hell of a long time with all that equipment,’ recalled Poulsson. ‘It was very tiring but because we moved from hut to hut our nights were fairly comfortable. The problem was food. We used up all our rations quickly and became very hungry indeed.’

Three weeks after taking off from Scotland, the W/T operator Haugland cabled London with a short message that offered only a few clues as to their ordeal. ‘Happy landing in spite of stones everywhere. Sorry to keep you waiting for message. Snow storm and fog forced us to go down valleys. Four feet snow impossible with heavy equipment to cross mountains.’

Ravenously hungry and starting to show the first signs of malnutrition, the party understood the importance of finding extra provisions to supplement their modest rations. To their delight, Haugland found a stray sheep and two lambs in a gulley. ‘We were very, very hungry at this time so we immediately killed one of the lambs and then skinned it on the floor of the hut,’ recalled Haugland. ‘We cut up the meat and put it into a big kettle with some dried peas . . . It smelled delicious and we all sat down at the table eagerly. But as one of the group (Poulsson) carried the kettle over to us, it dropped onto the floor. We all immediately got down on our hands and knees and even though the floor was very dirty we filled our plates with what we could and ate every last bit. It was delicious.’

Having recovered their strength, the men set out on daily reconnaissance trips to locate a landing place for the Commandos’ gliders. They found the ideal location – long, flat and free of rocks and other obstructions – to the south of Møsvatn, roughly ten miles from Vemork.

On 15 November, Haugland cabled London with the news that the snow at the landing place was 30 cm deep and frozen hard. If the weather stayed fine, he estimated that the march to Vemork would take the Commando force about five hours. SOE and Combined Operations held a meeting in London the same day to discuss the first Allied glider-borne operation of the war. They decided Operation FRESHMAN was to be launched in three days’ time, during the ‘moon period’, when the days either side of the full moon would offer good light for the RAF crews to pinpoint the landing zone. SOE put GROUSE on standby to prepare for their arrival. On the 18th, Churchill signed off a memo giving the operation the go-ahead.

The plan, in short, was for the Commandos to be led to the hydroelectric plant by GROUSE, fighting their way if necessary. After overpowering the German garrison there, the demolition teams were to break into the basement and destroy the heavy water canisters, fight their way back out against any reinforcements that had arrived in the meantime, then escape on foot across hundreds of miles of some of the harshest terrain on the planet to the Swedish border – but without skis. The wounded were to be given morphine and left behind. Operation FRESHMAN wasn’t officially designated as a ‘suicide mission’, but that is effectively what it amounted to. It was probably just as well the 34 Royal Engineers of the 1st Airborne Division selected for the task were kept in the dark about their objective until the very last moment.

Even in ideal flying and landing conditions, glider operations were perilous, nerve-shredding affairs, dreaded by the troops – and there were few countries less enticing for a glider pilot than Norway with its rough terrain and challenging, changeable weather. But at 1715 on 19 November, the conditions were as good and settled as could be hoped for and Haugland wired London a message to that effect.

The Royal Engineer paratroopers, heavily laden with weapons and equipment, filed out of the huts at Skitten Airfield near Wick and boarded the two Horsa gliders attached to Halifax bombers. There were seventeen men squeezed into each of the unpowered wooden aircraft, plus two RAF crew sitting at very basic controls. When they took off, just after six o’clock, the weather was fairly mild but the wind steadily picked up as they crossed the North Sea. By the time they reached the Norwegian coast, the gliders were bouncing through strong turbulence. One hundred miles inland, the GROUSE party waited anxiously at the landing zone, listening out for the rumble of the RAF bombers. But they never came.

The details of the Commandos’ fate would not become clear until the end of the war, but when only one Halifax bomber returned, the operation planners feared the worst. One of the gliders had crashed into a hillside at a place called Fyljesdal, close to the coast, after the towrope had frozen solid and snapped. Eight of the men had died on impact, one had injured his spine and was paralysed from the waist down, another had broken both his legs, one had shattered his jaw and a fourth had cracked his skull and had difficulty in breathing. Shortly after the crash, two groups of Germans had arrived, one party of regular Wehrmacht soldiers and another of SS troops under the command of a Gestapo officer.

The dead men were dumped in shallow graves and the Germans refused to let the locals give them a proper burial. The five uninjured men were taken to Grini Concentration Camp near Oslo where, after two months’ detention, they were taken into woods and executed. A War Crimes trial at the war’s end revealed the gruesome fate suffered by the four badly injured British troops at the hands of the Gestapo. Leaving one of them in the cell next door to listen to the torture of his comrades, the Nazi secret policemen battered the other three and strangled them with leather straps. When the Commandos were close to death, their torturers stood on their chests and throats and then injected air into their bloodstreams. All three died a slow death in agony. The fourth man was shot in the back of the head. Two of the torturers were sentenced to death for murder and the third was given life imprisonment.

The fate of the survivors in the second glider was equally disturbing, but the full details of the hours leading to their death have never emerged. An SOE agent reported that the glider crashed near a town called Egersund, killing two or three outright and wounding an unknown number of others. After ‘interrogation’, all the survivors were shot. The Halifax bomber towing the glider crashed into a mountainside after becoming separated, killing the six-man crew.

The catastrophe of Operation FRESHMAN was also a major setback for Allied efforts to wreck Germany’s atomic bomb programme. A map, with Vemork circled in red, had been found at one of the FRESHMAN crash sites. The Germans immediately set about strengthening the defences at the plant and sweeping the area for enemy agents. The GROUSE party was forced to disappear deep into the Hardanger until the danger had passed. SOE cabled them an urgent message, reading: ‘. . . vitally necessary that you should preserve your safety.’ As a further precaution the name of their operation was changed from GROUSE to SWALLOW.

It was now close to a year since the rate of heavy water production at Vemork had been increased by 3,000 per cent. No more time could be lost. Just days after the FRESHMAN disaster, SOE decided to launch a second attempt. This time it would be carried out by a small group of British-trained Norwegian Commandos disguised as British soldiers. The operation would be code-named GUNNERSIDE.

The new plan was as simple as it was daunting. A group of six men from the Linge Company was to be parachuted onto the Hardanger to team up with the Swallow/GROUSE party. The ten men would ski to Vemork, break or fight their way into the plant, destroy the heavy water and then escape to Sweden. Unlike their doomed comrades in FRESHMAN, at least this raiding party would have the benefit of skis – equipment that any Norwegian could have told the SOE planners was essential.

Joachim Rønneberg was just twenty-two years old but he was the obvious candidate to lead the raid and would assume command of the combined parties on arrival. ‘Rønneberg was one of the most outstanding men we had. He was well-balanced, unflappable, very, very intelligent and tremendously tough,’ wrote Colonel Charles Hampton, who ran SOE’s Norwegian training school in Scotland. Rønneberg was equally clear as to who he wanted to join him in a venture which would test their courage and physical strength, their will to survive and outdoorsmanship to the limit. ‘I wanted strong, physically fit men with a good sense of humour who would smile their way through the most demanding situations,’ he said. He chose Knut Haukelid, a formidable operator, as his second-in-command. In his SOE reports, his instructor describes Haukelid as ‘exceptionally efficient . . . cool and calculating type who would give a very good account of himself in a tight corner . . . A really sound man and cunning. Has no fear.’ He would show all these qualities in abundance by the time the mission had played out. The other four – only marginally less impressive than their leaders – were Birger Strømsheim, Hans Storhaug, Kasper Idland and Fredrik Kayser.

At a meeting with the SOE chiefs in London, Rønneberg and his men were made aware of the enormous risks of the operation. Just in case they were in any doubt about the fate they faced were they to be captured, they were told about Hitler’s famous directive ordering the summary execution of all British Commandos. Unknown to the Allies at the time, this had come into force a few days before the FRESHMAN disaster. Rønneberg recalled: ‘They told us everything – that those who had survived the crash were shot, or “experimented” on and that some were thrown into the North Sea. They told us that we would be given poison capsules so that we would not have to suffer the same ordeal.’

Using an exact life-size replica of the basement at Vemork, the sabotage party practised laying explosives on the cylinders over and over again until they could do it in the dark. Like SWALLOW, GUNNERSIDE were never told about the deadly capabilities of heavy water, only that its destruction was vital. Their ignorance of the stakes makes the risks they were prepared to take all the more remarkable.

GUNNERSIDE and SWALLOW were to meet at the prearranged landing place, but failing that they would all head to a hut known as Svensbu. After the raid, while the GUNNERSIDE team were to head for the Swedish border, the SWALLOW members were to disappear into the Hardanger and await fresh orders. The parachute drop was scheduled for the ‘moon period’ around 17 December, with the raid itself pencilled in for the night of Christmas Eve when it was hoped that the German garrisons would be less vigilant than normal. Shortly before they left London for Scotland, they were given a special address by Professor Leif Tronstad, the former chief scientist at Vemork, who had escaped to London and teamed up with SOE. His in-depth knowledge of the Vemork plant was key to the planning of GUNNERSIDE. ‘You have no idea how important this mission is,’ he told them, ‘but what you are doing will live in Norway’s history for hundreds of years to come.’

The survival of the SWALLOW party added to the sense of urgency. SOE knew their rations were virtually exhausted and that winter, with its ferocious blizzards and blood-stopping temperatures, was on its way. With German troops scouring the Hardanger area for British-backed agents and W/T operators, the SWALLOW party abandoned the hut at Sandvatn and moved into huts deep in the plateau, where there was even less chance of the Germans finding them. Not long after setting out, a ferocious blizzard blew in with winds so powerful that, according to Poulsson, ‘We often had to crawl along on all fours.’ It was the onset of one of the worst winters the area had experienced in living memory.

‘We had three tasks as we waited for GUNNERSIDE,’ said Poulsson. ‘The first was to stay alive, the others were to maintain radio contact with England and to establish contact with people who could give us information about what was happening at Vemork and what the Germans were up to.’

All four members of the party were in poor physical condition by this stage. All edible vegetation on the Hardanger had long since disappeared and the migrating reindeer had yet to arrive. To make matters worse, they soon exhausted their store of dry wood. Kjelstrup and Helberg both developed oedema and swelled by about twenty pounds. All four suffered from fevers and nausea. By the time they had reached the Svensbu hut, where they were to team up with GUNNERSIDE, the food situation had become critical. Their rations were all but finished. Only the very smallest amount, which they kept for the direst emergency (i.e. imminent death), remained.

Despite his own wretched state of health, and almost delirious with fatigue and hunger, Poulsson set out day after day, with his Krag hunting rifle slung over his shoulder, and skied for miles across the Hardanger in a desperate search for the reindeer herds. Day after day he staggered back to the hut, empty-handed. Finally, on 23 December, he caught sight of a herd on the distant horizon. The challenge now was to get within effective shooting range without startling them. That was no mean feat, even for a hunter of Poulsson’s experience. At the first sign of danger, reindeer flee, and Poulsson knew he lacked the strength to chase them for any great distance over the plateau. Quivering with excitement and nerves, Poulsson stalked the herd for over an hour. He knew the stakes. If they didn’t eat soon, he and his men would fall gravely ill and the operation would be placed in serious jeopardy. As he crept closer to the herd, exhausted from the effort and concentration, his foot gave way and he crashed to the ground. The two reindeer closest to him stamped their hooves to raise the alarm and the whole herd disappeared in a stampede over the crest of the hill. ‘It was enough to make a man weep,’ he said.

The sun was starting to sink behind the mountains as Poulsson dragged his weary body up the next slope. Poking his head over the top of the hill, he was relieved to see the herd had not run far. He lay down and lined up one of the closest animals in his sights. Three cracks split the still frozen air in rapid succession and the herd thundered away into the next valley. It seemed that he had missed. He could see no carcass in the snow and was just about to head back to the hut when, using his binoculars, he noticed what looked like a trail of blood in the snow. He raced forward as fast as his skis would allow him and there, just over the brow, was his injured prey. One further shot from his Krag and the beast slumped to the snow. Laughing wildly with relief, Poulsson took his mug from his rucksack and drank the warm blood spouting from the reindeer’s wounds before it froze. After skinning and butchering the animal, he packed the best parts into his rucksack, covered the rest to be collected later, and staggered back towards Svensbu, happy in the knowledge that the long weeks of starvation and malnutrition were over – for the time being at least. When the emaciated SWALLOW leader entered the hut, covered from head to foot in frozen reindeer blood, the other three cheered with joy.

That year’s Christmas feast was one that none of them would ever forget and, over the subsequent few weeks, the four of them devoured every last morsel of the reindeer, including nose, lips, brains and eyes. (‘The head was the best part,’ said Poulsson.) The food that did more than anything to keep them alive was the half-digested reindeer moss they found in the reindeer’s stomach. This was rich in vitamin C and carbohydrate, and mixed with blood and heated up came to be considered as a ‘delicacy’ by the men. Every part of the animal was put to use, including the pelts which were hung up around the hut for extra insulation.

The reindeer had saved their lives and, in doing so, it had rescued one of the most important operations of the Second World War. But bad news soon followed good. London cabled SWALLOW to inform them that the raid had been postponed for a further four weeks. Poor weather had prevented the RAF from dropping the GUNNERSIDE party. The temperature crashed so low on the Hardanger in January that hoar frost lay inches deep on the inside walls and ceiling of the hut. The boredom and frustration of the party was almost as intense as the cold. Helberg filled much of his time making reconnaissance trips to Vemork and his hometown of Rjukan, each time resisting the temptation to visit his family or seek out provisions of fresh food. He often slept in a hut right next to his family home and watched them come and go.

On 23 January the wireless set crackled into life with the news that GUNNERSIDE were on their way again. The four men rushed to lay out the lights at the prearranged landing site. A nearly full moon shone brightly in a star-studded sky. The weather could not have been better but, to the despair of all involved in the operation, the mission was aborted yet again. The Halifax circled over the Hardanger, but the navigator was unable to pick out the dropping zone and, running low on fuel, the pilot was forced to return to Scotland. Fury amongst the planners and the two raiding parties once again gave way to frustration and anxiety for another four weeks. The RAF had lost thousands of men flying behind enemy lines – many of them in Norway – and there was a widespread reluctance to criticise them but, according to the official report of the meeting called to discuss the aborted mission, the plane’s navigator was given a severe earbashing. Tensions were high; time was running out.

It was now over three months since the SWALLOW party had parachuted into the Hardanger. It was remarkable that they had survived that long. Could they hold out for another month? The twin pressures of malnutrition and perishing cold were pushing them to the limit. Throughout January and February, the temperature rarely rose above minus 30 degrees Celsius. With little to do but conserve energy and stay warm, they spent most of the time in their sleeping bags. On 11 February, they were put back on standby, but a few hours later a ferocious storm swept over the Hardanger. The winds were so strong it was impossible to move more than a few metres. Five days later, the skies cleared, the wind dropped, and GUNNERSIDE quickly scrambled aboard the Halifax to exploit the break in the weather. They took off at 2000 hours and it was beautifully clear when they approached the Hardanger. Just after midnight, the six men and eleven equipment containers plunged through the dispatching hole into the frozen night from a mere 700 feet. Moments later, they felt the thud of their homeland underfoot and they set about gathering up the containers littered over the landscape. There was no sign of the SWALLOW welcoming party.

They buried the equipment they didn’t need for the raid itself under the snow, placed marking stakes and took the bearings so that they could find the location at a later date. The wind was strengthening by the hour. Another storm was gathering. They knew they had to hurry to find Svensbu or some other form of shelter, and they had barely set out when they were engulfed by a violent blizzard. Battered by winds so strong they could move only with the greatest effort, the six men were beginning to fear the worst when they stumbled across a hut called Jansbu. It was a stroke of the greatest luck. Because the visibility was so poor, had the column of skiers been advancing thirty yards either side of it, they would have missed it. As the men warmed themselves by the fire and dried their clothes, the storm shrieked and roared, growing in force hour by hour. ‘You felt as if the whole cabin was going to be lifted off the ground,’ wrote Rønneberg in his official report.

They set out again when the storm appeared to be subsiding the following morning, but it was only a lull and Rønneberg quickly ordered them to turn back. The combination of powerful winds and deep drifts of snow made progress all but impossible. The storm howled for a week, during which the entire raiding party developed heavy fevers. Without any W/T equipment, they were unable to contact SOE. Sheltering from the same storm a few miles away, SWALLOW were gravely concerned for their comrades.

On 22 February, the storm lifted almost as quickly as it had descended. Clear skies and a dazzling sun revealed the Hardanger in all its snow-blasted glory. Leaving behind more nonessentials to be collected at a later time, they set out on what all knew was going to be a grinding march through tough terrain and extremely deep snow. Taking British uniforms and weapons for SWALLOW plus five days’ worth of rations and the demolition equipment, each rucksack weighed twenty-five kilograms. They also had two small toboggans weighing roughly forty kilograms.

As they left the hut, a man claiming to be a hunter appeared. The Commandos were under strict orders to kill anyone who might compromise the successful execution of the operation, but the Norwegians were reluctant to dispatch one of their compatriots unless they knew for sure he was a Quisling. The man gave his name as Kristian Kristiansen; uncertain whether he was a Quisling or ‘Jøssing’ (a good Norwegian), Rønneberg put him to work pulling one of the toboggans. He turned out to be an excellent guide and first-rate skier, an indispensable extra pair of hands during a gruelling march.

Later that morning, drooping with fatigue, they caught sight of two men skiing hard across the horizon. While the rest of them took cover, clutching their Tommy guns, Haukelid waited to greet them. The two men looked completely wild. Their clothes were caked in filth and reindeer blood, their beards were thick and unkempt, their faces drawn and unhealthy. It took Haukelid some time to register that it was Helberg and Kjelstrup! It was a joyful moment for the two parties. Finally, they had made contact – and all ten men were still alive. After four months of effort and delays, Operation GUNNERSIDE was on. ‘We greeted each other with as much emotion as Norwegian men can,’ Helberg recorded drily.

After the back-slapping and hand-shaking, they had to decide what to do with the reindeer hunter. Did they kill him or set him free and risk him jeopardising the operation? Rønneberg’s instinct told him that Kristiansen could be trusted but, as a precaution, he made him sign a statement that he owned and used a rifle, warning him that it would be handed to the Gestapo if he failed to hold his tongue. (The Germans threatened the death sentence for anyone found carrying a weapon.) They also gave him several days’ worth of rations in the hope he would stay up on the Hardanger until the raid was over.

By the time they reached SWALLOW’s hut, GUNNERSIDE had covered forty-five kilometres of heavy terrain in sixteen hours. It was an impressive achievement. They were shattered, but their spirits were soon lifted by a feast of reindeer dishes and the chance to exchange news with their comrades. There were just forty-eight hours to go before the ten Commandos launched one of the boldest and most important raids in the history of warfare.

On 25 February, leaving Haugland the W/T operator behind, the raiders set off in driving snow for the hut from which they would launch the raid. Fjosbudalen, as it was known, was the perfect launching point for the attack: close to the plant but difficult to access. Situated 800 metres above the valley, looking to their left was the town of Rjukan, strung out for 2 miles along the main road and the banks of the River Måna. About two miles to the right, hidden from view by a kink in the valley, lay the giant Vemork plant. The slope leading down to the Vestfjorddalen valley was extremely steep. Descending it would be hard enough; coming back up would be punishing.

Following Operation FRESHMAN, a raft of measures had been taken to beef up security at Vemork and in the surrounding area. A detachment of 30 first-rate German soldiers had arrived to take over the defence of the plant itself, the garrison at Rjukan increased to 200, and at the Møsvatn Dam, troop numbers were quadrupled to 40. Batteries of anti-aircraft guns and searchlights had been installed.

From intelligence from inside the plant and Helberg’s recce trips, they knew that every night two guards patrolled the suspension bridge across the gorge connecting the plant to the main road; the guards changed over on the stroke of midnight and floodlights would illuminate the entire plant and immediate area in the event of an emergency.

How to access the plant was an issue that provoked a great deal of debate among the raiders. If they tried to fight their way in over the bridge, the German reinforcements from Rjukan and Møsvatn would quickly be on the scene. If they were to become involved in a prolonged gun battle against a vastly superior, more heavily armed force, there was a risk that they might not be able to lay the explosives. It was unlikely any of them would escape either. If they survived the fight and were captured, they would be summarily executed as Commandos. Still, a minority of the party, including Rønneberg, argued that this approach gave them the best chance of success.

There was one possible alternative. At first light on the day of the attack, Helberg made a final recce to see if it was possible to climb the gorge. The Germans thought it impossible and never patrolled that end of the plant that Helberg had pinpointed. If it was possible to scale the virtually sheer icy wall of rock, it would give the saboteurs a number of advantages. There was a much greater chance they could enter the plant unnoticed, avoid any contact with the enemy and prevent the alarm being raised until the charges were detonated. It also meant they could leave the equipment and provisions for their escape at the hut, allowing them to carry only their weapons and demolition kit, and therefore escape more quickly.

Either way, with giant searchlights lighting up the plant and hundreds of troops scouring the area, the chances of all nine men escaping were very slim. This was partly because the Germans would work out that there was only one exit route open to the saboteurs – up the steep slope opposite the plant. Behind the plant was a towering cliff almost one kilometre high, and taking the only road through the valley was not an option. To get out of Vemork, they must either cross the bridge or climb back down the gorge, negotiate the river, cross the main road and then make the energy-sapping climb up the same, near-sheer valley wall they had descended earlier. The party was as good as resigned to not making it to safety. ‘Our chances of being trapped in the valley were very great indeed,’ recorded Rønneberg. ‘We knew that we might not come through it.’

When Helberg returned from his mission, he revealed that though the ice on the river was starting to thaw, there was a narrow point where they might be able to cross. On the other side, he pointed out, there was a band of small trees linking the bottom of the gorge to the plant. If trees could climb the gorge, so could they, Helberg argued. A vote was taken and the climbing option carried the day. The group were split into two: a covering party led by Haukelid and consisting of the SWALLOW members Helberg, Kjelstrup and Poulsson, and the demolition party led by Rønneberg and including Strømsheim, Kayser, Idland and Storhaug. Their operational orders covered every possible eventuality. ‘If fighting starts before the High Concentration (heavy water) plant is reached the covering men shall, if necessary, take over the placing of the explosives. If anything should happen to the leader, or anything to upset the plans, all are to act on their own initiative in order to carry out the operation. If any man is about to be taken to prisoner, he undertakes to end his own life.’ The raiders weren’t aware of the stakes that rested on the raid. Were they to fail, the Allies had just two courses of action left open to them: a saturation bombing raid that would most likely claim the lives of scores of their compatriots, or blowing the dam and flooding the valley, killing hundreds of innocent Norwegians, including dozens of their own family members.

The conditions were perfect when the nine saboteurs, dressed as British soldiers and carrying British papers, left the hut at 2000 hours and began the long descent. It was cloudy and windy. What they didn’t want was a still night with a bright moon. They were travelling light, which was just as well, given the intense physical exertions ahead of them. Between them they carried five Tommy guns, three Colt .32 pistols, seven Colt .45s, ten Mills bomb hand grenades, two sets of explosive charges and fuses and a small quantity of food. The wet snow was three feet deep in places and made it impossible to proceed on skis. Advancing on foot, with their skis and poles slung over their shoulders, the men regularly sank up to their chests in the drifts. On reaching the powerline, they buried their skis, dashed across the main road and disappeared into the darkness at the bottom of the gorge as fast as the snow and rock allowed them.

The river ice was thawing rapidly in the mild air and the one stretch that Helberg had singled out as passable now had three inches of water running over it. The ice cracked as, one by one, they shuffled across to the foot of the cliff. Looking up at the virtually vertical rockface, there was some doubt cast on Helberg’s optimism, but one after the other, they yanked themselves upwards, grasping roots and branches and icy outcrops for support. One slip or loose stone and they would tumble to their death. All nine men were first-rate outdoorsmen and there were no mishaps, although by the time they scrambled onto the railway tracks at the top they were sodden with sweat from the strain.

A few hundred metres along the tracks, they could just make out the dark outline of the Vemork plant’s two enormous main buildings. The faint rumbling of the machinery inside was carried along on the wind. Like clockwork, on the stroke of midnight, the two sentries pacing up and down the suspension bridge were relieved by a new pair. In planning the fine details of the advance, the raiders had decided to wait for thirty minutes, figuring the vigilance of the guards would start to fade. The nine men sat patiently in the shadows of the towering cliff at the eastern end of the plant before making their move. They crept towards the plant’s fenced perimeter and crouched. Haukelid sprinted up to a set of high wire-mesh gates and snapped the thick chainlock with a pair of shears. The covering party were the first into the compound, bursting through the gate to take up their positions. The demolition team followed and quickly broke open a second gate leading to the basement where the heavy water was stored. So far so good. The only setback was that the moon had appeared and some of the lights inside the factory had been left on.

Leaving one man on guard, the other four members of the demolition party split into pairs. A cellar door and a second entrance that were meant to have been left unlocked by a contact inside Vemork hadn’t been. (The contact, it transpired, had been taken ill and failed to come to work.) Thanks to Tronstad’s meticulous planning of the operation, one option remained: Rønneberg and Kayser climbed a ladder and crawled into a narrow cable shaft. Pushing their demolition equipment ahead of them, it took several minutes to wriggle their way to the far end of the shaft. They slid down a ladder and burst into the room housing the cells of high-concentration heavy water, overwhelming the terrified Norwegian guard. After locking the doors, Kayser held the guard while Rønneberg set about laying the sausage-shaped explosive charges on each of the eighteen cylinders. Both men were at pains to show the guard the insignia and stripes on their British uniforms. Fearing reprisals against the local population, they left further evidence, in the form of their English-made tools, that this was a British operation, and not one carried out by the Resistance.

The original plan was to lay two-minute fuses but, fearing that would give the plant engineers time to dismantle them, the raiders opted for shorter versions – a courageous decision that increased the risk of the party getting caught before they had cleared the compound. Rønneberg was poised to light the fuses when a Norwegian civilian walked into the room. Visibly taken aback by the sight of the Commandos, at the point of Kayser’s gun he was made to join the guard with their hands above their heads. Outside, the covering party were getting worried. It had been almost half an hour since they had seen the demolition team.

When Rønneberg lit the last of the fuses, Kayser ordered the two captives to sprint upstairs as they all made for the cellar door. The door had barely shut when they heard the first of eighteen muffled explosions from behind the thick stone walls. Within seconds, one and a half tons of concentrated heavy water – the essence of Germany’s atomic bomb programme – was gushing across the floor into the drains. The strong wind had helped soften the thump of the charges. Loud noises were not uncommon in the valley at this time of year in any case. Ice cracked and large quantities of snow often fell down steep slopes, especially during the thaw. But expecting some reaction from the garrison all the same, the nine raiders took cover and waited. Sure enough, the door of the barracks house swung open and the silhouette of a soldier appeared in the light from within. Swinging a torch from side to side, he moved slowly towards some tin drums. Haukelid was crouched behind them. There were three Tommy guns and five pistols pointing at the soldier’s back as he pulled up just short of the drums, a few feet from Haukelid. The beam of his hand torch brushed the Norwegian’s head; his comrades flicked off their safety catches. The guard stood for a few moments, then turned slowly and made his way back to the barracks. As the door shut, Rønneberg gave the hand signal for the team to pull out.

The next few minutes were to be critical. It was imperative they put as much distance between them and the plant as possible before the alarm was raised. Clambering to the foot of the gorge as quickly as they could without risking a fall, they found the Måna was flowing much faster than it had been just a couple of hours earlier and the ice was that much more unstable as they dashed across. Hauling themselves up the icy bank towards the main road, the party froze on the spot when the eerie wail of the plant’s alarms broke the night’s silence. Grabbing their skis and poles, the nine men melted into the darkness of the woods at the foot of the slope before them.

Walking switchback rather than straight up the steep slope, several kilometres and hours of draining marching lay ahead of them, but with every German soldier in the region pouring into Vemork, they had all the motivation they needed to press on without delay. Their route followed the open area beneath the cable car used by sun-starved locals in the winter to get onto the plateau above the town. It was the only plausible route, but there was a danger that the plant’s searchlights might reveal them, and the Commandos were surprised that the lights had not been turned on immediately. An even greater worry was that the Germans would turn on the cable car and dispatch troops to the top, but that fear was never realised either. At 0500, after three hours’ backbreaking marching, they dragged their weary bodies the final few steps onto the plateau above.

‘It was a beautiful morning as we watched the sun rise,’ recalled Rønneberg. ‘The sky was lit up in a lovely red colour and we sat there in silence eating chocolate and raisins . . . We were all very, very happy. Although we said nothing as we sat there I think we all felt great pride. But we also spared a thought for our British friends who died in the gliders disaster . . . From now on our struggle was with Norwegian nature.’

The next stage of the escape was to head for a hut owned by a Rjukan shopkeeper at a remote location called Langsja where they would rest up before heading back to the Svensbu hut. The wind howled over the Hardanger as they set off and, having not slept for the better part of two days, it was a major effort to drag their aching limbs against the force of ever-strengthening gusts. They made it to the hut with no more than an hour to spare before another violent blizzard burst over the plateau. Although they were unable to press on, the fresh snow did at least cover their tracks from the cable car and force the Germans to spread their troops over Telemark’s vast wilderness.

In the valley below, the Germans were struggling to understand how the ‘impregnable fortress’ of Vemork had been breached and its precious contents destroyed without so much as a shot being fired. General Wilhelm Rediess, the head of the Gestapo in Norway, urged reprisals against the local population after inspecting the damage, despite conceding that the raid had, in all probability, been a British operation. General von Falkenhorst, commander of German forces in Norway, overruled him on the grounds that it had been a military act. Von Falkenhorst, an old-fashioned Wehrmacht officer with a distaste for the practices of the Gestapo, was in open admiration of the raiders, describing the attack as ‘the most splendid coup I have seen in this war’. He was later dismissed from his post for refusing to implement the policies of the Nazi Reichskommissar Josef Terboven who, amongst other brutal acts, had ordered savage reprisals against the villagers of Televåg for sheltering two Norwegian officers.

After a good night’s rest and revitalised by some hot food and drink, the GUNNERSIDE party set out the following morning into the snowstorm for Svensbu. It was tough going and it wasn’t until 2130 that they finally arrived. At the start of what would turn out to be a heart-stopping personal adventure, Helberg peeled off to return to the Fjosbudalen hut to collect the civilian clothes and faked Norwegian identity documents he would need over the coming months. The plan was to meet the rest of the team at Svensbu, but there was no sign of him over the next two days and his comrades feared for his safety.

At this point, the eleven men of the operation (including Skinnarland, the local SOE agent) were to split into three separate groups. Five of the GUNNERSIDE party – Rønneberg, Idland, Kayser, Strømsheim and Storhaug – were to make a 400-kilometre journey to the Swedish border. Haukelid and Kjelstrup were to stay in the Hardanger, wait for the German searches to pass and then team up with the Resistance. Poulsson and Helberg were to head to Oslo before deciding on further action. Haugland and Skinnarland, the W/T operators, were to lie low until it was safe and await further orders from London. Convinced that Helberg had either been captured or killed, Rønneberg and his team strapped on their skis and pushed off for the long cross-country trek towards neutral Sweden.

For eleven days following the raid, the British authorities, including the Prime Minister, waited anxiously for news of the outcome. Haugland and Skinnarland had been unable to find a message left for them by the sabotage team at one of the huts they had been using. It was only when Haukelid and Kjelstrup arrived that they learnt the good news. Shortly before midnight on 10 March, the wires back in the UK came to life and the coded message began to arrive. Deciphered, it read: ‘Operation carried out with 100 per cent success. High Concentration plant completely destroyed. Shots not exchanged since the Germans did not realise anything. The Germans do not appear to know whence they came or whither the party disappeared.’ SWALLOW’s momentous message was greeted with relief and delight in Downing Street, Whitehall and the SOE HQ in Baker Street. Hitler’s hopes of beating the Allies to an atomic bomb had suffered a major setback – but, as events were soon to show, Operation GUNNERSIDE had not killed off his hopes once and for all.

Such was the urgency attached to capturing the Vemork saboteurs that General von Falkenhorst and the dreaded Terboven, the two most senior Germans in Norway, personally supervised the search over the weeks that followed. The senior officer at the Vemork plant was dispatched to the Eastern Front as punishment. At the height of the searches, over 2,000 German troops were deployed, as well as several hundred Norwegian Nazis from Quisling’s NS party.

When the sabotage party had set out to Vemork, Haugland and Skinnarland packed up their W/T apparatus and set up camp high in the mountains above Lake Møsvatn where they knew the Germans never ventured. From the safety of their snowhole, through the binoculars they watched the German troops combing the valley. A state of martial law was declared in the Telemark region with no one allowed to leave without official permission. The Norwegians, however, laughed at the incompetence of the Germans’ hunt for the perpetrators. Looking for suspicious ski tracks was an obvious place to start, but with so many soldiers involved they ended up creating an enormous confusion of tracks that killed off any leads.

Eager to avoid the more populated areas of eastern Norway, Rønneberg had decided to take the long route to Sweden, heading north at the outset before turning back to the southeast. SOE had made up three sets of escape maps, each of which contained twenty-six smaller, more detailed ones of the areas they would pass through. The weather and skiing conditions had been first rate when they had set out, but it wasn’t long before they hit trouble. Their rucksacks were heavy with equipment and poorly designed: the straps bit hard into their shoulders and put extra strain on their backs. They also had to heave a heavily loaded sledge, which was a gruelling effort through the wet snow and over rocky scrubland. Even Rønneberg, not a man to complain easily, recorded in his notes for the operational report that their escape was ‘an awful labour’.

Making sure they weren’t spotted added to the effort, forcing them to take detours around open spaces, main roads, towns and villages. Before each short stretch of the journey, two of them went ahead to reconnoitre the area before the others followed. The landscape, often shrouded in fog or snow, was a bewildering confusion of hills, valleys, forests and lakes, criss-crossed with tracks and paths. Unable to establish their location from the maps, they often had to rely on the compass to guide them. On several nights they were forced to sleep in their sleeping bags in the open, wet through with freezing sweat and melted snow.

On the fifth day, their spirits now at a very low ebb, the temperature plunged again but, in a rare stroke of good fortune, they came across an unoccupied farmhouse where they helped themselves to the stores of flour and bannock bread (hard, unleavened biscuit-style bread). In the remote regions of Norway, where many people kept huts or second homes, it is a custom to let strangers use them on the understanding that they replace, or leave some payment in kind for any provisions they use. Needless to say, the saboteurs weren’t in a position to repay the generosity.

On the evening of the sixth day, they crawled on all fours over a lake that was starting to thaw in darkness, climbed almost 1,000 metres of steep hill before breaking into a hut. The following day, the temperature rose sharply, which was a mixed blessing because it made the snow wet. By the afternoon, it was raining, and progress became even slower and exhausting; by nightfall, the sodden conditions forced the exhausted party to stop. Over the days that followed the party made good progress, but there were fresh problems: as winter continued its jostle with spring, the temperature dropped again, and their supplies were rapidly running out.

Unable to find a hut to break into, for two nights they were forced to sleep in the snow in their sleeping bags. With their rations almost exhausted, they had to veer from the route to seek out provisions, raiding huts for flour and bannock bread. The nearer they got to the Swedish border, the more alert they had to be, as there was a greater concentration of German and Norwegian Nazi units there. Navigating was more straightforward when they were high up because they could see the land and consult their maps, but down in the valleys it was far harder to work out where they were. The raiders were tantalisingly close to freedom when they got lost in the mesmerisingly uniform landscape.

They were heading for the Glåma, the longest river in the country, which runs roughly parallel with the border. When they found it, they were dismayed to discover it was entirely free of ice. They were forced to steal a boat to cross it. The following two nights were spent out in the open again in wet clothes and sleeping bags. No one slept. They were too cold and too hungry. The final leg was especially hard-going. ‘It was dreadful broken and stony country, through scrub and thick woods, with no visibility,’ Rønneberg noted.

Finally, just after eight in the evening on 18 March, 400 km and two weeks after they had set out, bedraggled, worn out and famished, the five men crossed into neutral Sweden. They shook hands, slapped each other on the back and, best of all, lit their first fire in the outdoors since leaving Britain. The following morning, after burying all their incriminating equipment, they changed into civilian clothes and walked along a main road until they were picked up by a police patrol and taken to the local sheriff and then to hospital where they washed and had their clothes disinfected and dried. The following day, the Swedish police happily accepted their cover story that they had escaped from a German work camp. Issued with the relevant identification papers, they continued to Stockholm and reported to the British legation, who arranged for their return to the United Kingdom.

SOE were quick to understand the trials the men had overcome during their arduous escape. ‘The difficulties of this march in winter conditions with the added strain of short rations and hard lying make it a most noteworthy achievement,’ an SOE memo states. Back in Britain at the end of March, Rønneberg noted movingly about his adopted country: ‘On our arrival we were handed a cup of tea. It was a strange feeling because here I was back in Britain, but I felt like I was at home. We often used to refer to it as home when we were in Norway and when I look back on the war I will never forget the welcome that the British showed us.’

Rønneberg, meanwhile, had compiled a comprehensive report of the raid (which can be read in the National Archives at Kew), attached to which is a handwritten message from a senior government figure (only a very few knew of the heavy water threat). It reads: ‘A magnificent report of a great effort. Well planned and beautifully executed. If you return the report to me I will have a condensed edition made for the P.M.’

The destruction of the heavy water and the safe return to the UK of the men who carried it out was by no means the end of the story. There was a great deal of drama to be played out yet. In early April, SWALLOW reported to England that Helberg had been shot trying to escape the Germans. Tributes were duly paid by SOE and his Norwegian comrades. This was wrong. Helberg was very much alive and enjoying a remarkable adventure. The story of his escape, which he wrote up on his return to the UK, amazed even his SOE commanders, who witnessed plenty of high adventure in their roles. His boss Colonel Wilson scrawled a note on Helberg’s report: ‘The attached is an epic of cool headedness, bravery and resource.’

After the raid, Helberg and Poulsson both headed east for Oslo and met, as arranged, in a café the following week. Poulsson left for Sweden a few days later in order to return to Britain. Helberg’s long-term plan was to make contact with the resistance movement Milorg back in Telemark after lying low for a few weeks while the Germans hunted for the raiders. In the short term, his main priority was to move to a safer place the cache of incriminating equipment that GUNNERSIDE had left near the Jansbu hut where they had sought refuge from the snowstorm after their parachute drop. Were the Germans to find it, there was a strong risk of reprisals against the locals, dozens of whom had already been arrested and taken in for interrogation. After a couple of weeks in Oslo, Milorg said it was safe for him to return to the Hardanger. He left Oslo on 22 March, unaware that the Telemark region was in fact still crawling with Germans.

Helberg spent his first night back on the Hardanger in a hut that was burnt to the ground the following day. The Germans – furious at being unable to track down the ‘British’ saboteurs – were venting their fury on the locals. Still oblivious to the large concentration of German troops in the area, Helberg skied off to the Jansbu hut. Pushing open the door, he found the entire contents of the hut strewn all over the floor. He immediately turned round and saw three German soldiers skiing towards him at speed. Quickly strapping his skis back on, Helberg took his Colt .32 from his rucksack and put it in his pocket. As he pushed off, the Germans opened fire on him, the bullets kicking up puffs of snow around him. ‘I increased my pace so they had to stop shooting and then a first-class long-distance ski race began,’ recalled Helberg in his official report. ‘I had a half year’s training to my credit and was in splendid form.’

Two of the Germans turned back after an hour or so but the third, a very strong and accomplished skier, kept up the chase. Helberg was a strong uphill skier so he headed for the mountains in the hope of shaking him off. He also skied straight into the low, brilliant bright sun in order to dazzle the German if he attempted a potshot. Helberg was weighed down by a heavy rucksack and his skis were in a poor state because he had not had a chance to wax them. Slowly the German gained on him. After about two hours Helberg reached the lip of a steep hill and, fearing his pursuer would catch him on the descent, he decided to stop and settle the matter in a shootout. The German pointed his Luger at him and bellowed ‘Hande hoche!’ (‘Hands up!), but was taken aback when Helberg pulled out his Colt .32. Helberg stood stock still and let the German empty the whole magazine of his pistol. He knew the Luger was not effective beyond a range of about fifty yards and the German was further away than that. When he had fired his last bullet, the hunter became the hunted. Helberg quickly closed on him, took aim and fired. The German slumped to the ground.

Darkness was fast enveloping the Hardanger as Helberg headed back down to the floor of the valley. Halfway down, he felt the earth disappear from under him – he was falling over a very high precipice, as high as forty metres, Helberg estimated. His landing was cushioned by deep snow but he knew instantly that he had broken his left shoulder. To his relief, his skis remained intact and he pressed on, in excruciating pain and exhausted after a day and a half on his skis. Heading towards a town called Rauland where there was a house he knew, he was stopped by a German patrol. Unruffled as ever, Helberg calmly produced his identity card and told the Germans that he had been helping in the search for the British saboteurs. When he arrived at the house, he was disappointed to find it occupied by a group of German soldiers, but once again he passed himself off as a pro-German and settled down for a night of cards and drinking games. So well did he get along with the men who had been tasked with hunting him down, that one even bandaged up his arm in a sling and arranged for him to see a German doctor.

The following day a German Red Cross car was laid on to transport the smiling British-trained Commando to the town of Dalen. There he was to spend the night in a hotel before continuing to Oslo by boat and train for hospital treatment. It was typical of Helberg’s run of luck that Terboven, the country’s ruthless Reichskommissar, arrived at the hotel that night to use it as a base from which he could conduct the searches. Terboven moved into the room next door and SS guards were posted along the corridor. Helberg was caught in the centre of the spider’s web.

Early the next morning, hours before sunrise, a Gestapo officer ordered Helberg to join the other Norwegian guests in the lobby where they were made to wait for six hours. This was a nerve-racking time for Helberg. Not only was he the only single person among the guests, he also had a suspiciously sunburnt, weather-beaten face that could only have been acquired from spending a very long period out in the open. Finally, an officer arrived to explain why they had been rounded up. At dinner the previous evening, an attractive young girl had spurned Terboven’s public overtures and insulted him. Enraged by this display of Norwegian defiance, the Reichskommissar had ordered that all the guests were to be sent to the notorious concentration camp at Grini. Women over fifty and very elderly men were allowed to stay, but the seventeen others were shepherded onto a bus and told that they would be shot on the spot if they attempted to escape. An SS guard sat at the front of the bus by the only door and three more SS men were on motorbikes with sidecars in the escort.

Sitting next to the pretty girl whose boldness had so enraged Terboven, Helberg deliberately struck up a loud, boisterous conversation with her in order to draw the attentions of the SS guard. Sure enough, the German, like a bee to a honeypot, made his way to the back of the bus and indicated that he and Helberg were to swap seats. As the bus slowly negotiated the winding, climbing road, Helberg saw his chance, pulled open the door and leapt out. He hit the frozen ground hard, aggravating his shoulder and smacking his head. He ran into the woods, chased by the shouting Germans. Reaching a high fence that he could not scale, a stick grenade exploded a few yards away, hurling him to the ground. He hauled himself up, sprinted back past the bus and into the dense woods on the other side. A grenade exploded behind him and another hit him in the back, but it didn’t go off until he had scampered clear of its blast range. The Germans fired intermittently into the dark, but after a few minutes they returned to their vehicles and continued their journey. It was these shots that led to the report given to SWALLOW by the Resistance that Helberg had been killed as he tried to escape. To avoid punishment for allowing him to get away, the German guards probably reported that they had killed him.

That night Helberg sought sanctuary in a lunatic asylum in a town called Lier where he had heard that the staff were Jøssings. It was past midnight when he arrived, exhausted, soaked to the skin from the cold rain, and his shoulder and head throbbing with pain. He was immediately taken in, fed, washed, clothed and treated by a doctor. In the morning he was taken five miles down the valley to a hospital in the larger town of Drammen, where he was treated for eighteen days before being released. At the end of May, after three months as a fugitive in his country, Helberg escaped into Sweden and boarded a plane for Britain.

Estimates that it would take a year before the Vemork heavy water plant would return to its preraid operational levels proved wide of the mark. The Germans went to great lengths to repair the damage quickly, replace the destroyed apparatus and resume full-scale production. In July, Skinnarland cabled London with the depressing news that production would be back to full capacity within a month. Once again, the top brass in Whitehall convened to consider their options. Nothing was ruled out.

A ‘coup de main’ attack, similar to the GUNNERSIDE raid, was out of the question. Germans had made major improvements to their defences at Vemork, surrounding the plant with rows of thick barbed-wire barriers and minefields. All doors bar the main entrance to the building were bricked up and the windows had wire meshes fitted to stop bombs being thrown or fired through them. More troops had been drafted in to beef up the garrisons.

The only plausible option was a saturation bombing raid. The major drawback of such a plan of action was that innocent Norwegians were likely to die and the entire plant, upon which the local economy depended, would probably be razed to the ground. (Fertilisers for agriculture made up roughly 95 per cent of Vemork’s production.) ‘Precision’ bombing was little more than an expression in World War Two. The reality was that bombers dropped their payloads over the area of the target from a great height and hoped enough of them scored a direct hit. With the heavy water stored in the basement of a solidly built concrete and stone structure, hundreds of heavy, high-explosive bombs would have to be used.

The Norwegian authorities in London were sure to protest vehemently and an SOE memorandum of 20 August 1943 suggested that their High Command and government-in-exile should be kept in the dark about the plans. For the Allied authorities the deaths of innocent civilians and damage to a small local economy was a price worth paying to halt a programme that might wreak far greater destruction in times to come.

One man who didn’t indulge in too much soul-searching over the air raid was Major Leslie Groves, the head of the US atomic bomb project known as ‘Manhattan’. He insisted that the destruction of the Vemork plant was an urgent priority for the Allies and it was partly down to his powers of persuasion that the US government overcame its misgivings and rubber-stamped the plan. The job of carrying out the raid was handed to the US 8th Air Force. The first the Norwegian authorities in London were to hear of the attack was after it had taken place.

On 16 November, a massive fleet of 300 Flying Fortresses and Liberators roared off from the US bases in East Anglia and turned for Norway. Almost half of them split away from the main force to draw off the Luftwaffe fighters. The remaining 162 made a straight line for Vemork. The first wave of aircraft were 20 minutes early and, knowing that the Norwegian workers would not yet have left the plant for their lunch break, they made a circuit to kill time. This humane gesture was to prove costly. When the bombers returned the German gunners were waiting for them. Almost immediately the air was thick with smoke from the bombs, the steam in the cold air, the aircraft exhaust fumes and puffs of flak. From the outset, the plant was almost completely obscured and from 12,000 feet, it was more in hope than expectation that the Flying Fortresses and Liberators dropped 711 thousand-pound bombs and 201 five-hundred-pound bombs in just 45 minutes.

Almost all of the bombs missed the target and caused widespread devastation in the usually quiet and peaceful valley. The RAF photographs and the intelligence sources on the ground confirmed the planners’ worst fears. Far from destroying the plant and its heavy water stocks, Vemork had barely been scratched. Out of the 1,000 or so bombs dropped, only 18 landed on the site. Some of the power had been knocked out – but that was easily fixed – and several inconsequential outbuildings destroyed, but the operational capacity remained entirely unaffected. To add to the despair, an air-raid shelter full of women and children was hit. Twenty-two locals were killed in all. The Norwegian authorities back in London were enraged and a furious argument ensued that jeopardised future cooperation on vital missions – not least on how they might now proceed with a new plan to destroy Germany’s atomic capability.

In a further unwelcome consequence of the raid, the Germans decided that the heavy water was too vulnerable to be stored in Norway and they began making plans to move the operation to Germany. The intelligence caused panic in London and Washington and a blizzard of top secret memos blew down the corridors of power in both cities. The Germans planned to transport the heavy water to Hamburg, by train, ferry and then ship; the Allies planned to intercept and destroy it en route. Such was the urgency, the memos make clear, that likely reprisals on the local population were accepted as a price that would have to be paid for the destruction of the deadly cargo. On 7 February SWALLOW (Skinnarland) cabled London to report that the heavy water was going to be moved out of Vemork in the near future. The situation was now so critical that the news was immediately passed on to Churchill’s War Cabinet. Within an hour of sending his message, Skinnarland received an urgent message ordering him to organise an attack.

There was only one realistic candidate for the job: Knut Haukelid, the one member of the GUNNERSIDE party to remain in the area. Skinnarland tracked him down at his hideaway thirty miles away on the Hardanger. Under normal circumstances, Haukelid would have wanted several weeks to plan his attack down to the last detail, but time was not a luxury he enjoyed. To compound the challenges, the Germans had recently stepped up their sweeps of the area, hunting out the Resistance, and his journey back to the Rjukan area on 13 February was fraught with danger.

Skinnarland received hard information from his contacts that the heavy water was to be loaded onto a ferry, called Hydro, on the night of 20 February at the heavily guarded dock area at Mael, ten miles along the valley from Vemork. Haukelid’s plan was to blow up the ferry when it was over the deepest point of Lake Tinn. To do so, he would have to somehow find a way past the guards, get onto the ferry, lay the charges and escape before it set sail. The ferry was the principal link to the railway network and was frequently used by the locals. Many of them were certain to die if Haukelid was able to pull off his bold plan.

In the days leading up to the heavy water’s removal, dozens of Gestapo agents arrived in Rjukan to reinforce the army detachments and local police. Skinnarland’s agents, working inside Vemork, arranged the programme for loading the heavy water in such a way that it would leave on the Sunday ferry. On Sunday there was only one scheduled trip from Mael, which meant there was little chance of the Germans postponing its departure. What’s more, with most locals resting at home, it was likely there would be fewer casualties.

Haukelid built two rudimentary time-bombs using alarm clocks with traditional bells on top. The hope was that at the exact time he predicted that the ferry would be in the middle of the lake, the hammer would strike the alarm bell and detonate the charges. The risks were obvious – any heavy movement of the boat could set off the homemade devices at any time – but, given the haste and the urgency, there was no obvious alternative. On 18 February, Haukelid made a recce to Mael, bluffed his way onto the ferry and disappeared into the holds to work out where best to lay the explosives. He found his answer in a watertight compartment in the bow of the boat where crew members were highly unlikely to venture.

Haukelid couldn’t carry out the raid on his own. He needed help to carry the explosives, he needed a driver and he needed lookouts. The three men chosen to help were confirmed patriots: Rolf Sørlie, a member of the Resistance, plus Alf Larsen and Knut Leir Hansen, who were both engineers at Vemork. Only Sørlie, of the four, would remain in the area. The rest would flee to Sweden.

While Haukelid was carrying out his recce, the Germans began to load the heavy water stocks onto the freight wagons amid the tightest security at Vemork. Under the bright glare of giant floodlights, one by one the thirty-nine drums were carefully stored and secured. Twenty-four hours later, the train pulled slowly into the Mael ferry port. At 0100 Haukelid and his three accomplices set out from Rjukan. Leaving Larsen at the car, the others completed the last stage by foot. Bravado and composure under pressure were the order of the day from here in. Striding into the port as if they were dockyard workers, they passed the guards standing by the freight wagons lit up by floodlights. Incredibly, there appeared to be no German on the boat or guarding the entry to it, and most of the crew were playing cards at the far end of the boat. They darted below deck where they were confronted by a crew member. Haukelid had no choice but to take a gamble. He told the man they were Jøssings on the run and needed somewhere to hide their belongings. Happily, the man nodded and let them through. Haukelid also now had the perfect excuse if he was discovered in the depths of the boat.

Haukelid and Sørlie descended to the third-class deck where they wriggled through a hole in the floor into the bottom of the vessel. It was pitch black and there was freezing cold water a foot deep, through which they were forced to crawl with no more than eighteen inches between the water and the deck above. Working by torchlight in the very confined space, Haukelid fastened the charges to the wall and set the alarm for 1045. A few millimetres separated the bell hammer from the detonator.

The three men slipped out of the dockyard and melted away into the night. Haukelid was sitting on a train to Oslo the following morning, nervously inspecting his watch as it ticked down to 1045. The following morning’s newspapers carried the news: the ferry had sunk at the deepest point of the lake, just as Haukelid had hoped. Skinnarland sent the following telegram to London: ‘The Ferry was sunk on Sunday. Unfortunately some people drowned. Our people are OK.’ A further telegram from SOE in Stockholm confirmed the news, stating that the 500-ton ferry had gone down in three minutes with the loss of eighteen lives, fourteen Norwegian and four German. Nineteen people were rescued from the icy waters.

News of Haukelid’s brilliant coup was greeted with joy in London and Washington. Hitler’s hopes of beating the Allies in the race to build an atomic bomb now lay 1,000 feet below the surface of Lake Tinn. With the Allies now in the ascendancy on the battlefield, the Führer’s last chance of victory had been sunk.

Buried in the bundle of SOE documents relating to the raid at the National Archives in Kew is a small, frayed memo dated 14 April 1943, which reads: ‘What rewards are to be given to these heroic men?’ The identity of the man asking the question is given away in the address: 10, Downing Street, Whitehall. It is signed off with the initials ‘W.S.C.’ No one had followed the drama of the heavy water mission more closely than the Prime Minister, and no one was more eager to recognise the courage and skill of the young men who brought about such a happy ending to the saga. Rønneberg and Poulsson were duly rewarded with the Distinguished Service Order, the Military Cross was granted to Haugland, Idland and Haukelid, and the Military Medal to Helberg, Kjelstrup, Kayser, Storhaug and Strømsheim. Skinnarland was awarded the Distinguished Conduct Medal later in the war. When the full story of the Telemark raid emerged after the war, there were many who felt the eleven men deserved a great deal more.

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