How a daring raid by Norwegian commandos kept the Nazis from building a nuclear bomb

• In late February 1943, nine commandos set out of daring raid against the Germans in the Norwegian wilderness.
• Their mission, to destroy a plant producing heavy water, would fulfill one of the Allies' most important goals: Prevent the Nazis from building an atomic bomb.

At 8:00 p.m. on February 27, 1943, nine Norwegian commandos trained by the British Special Operations Executive (SOE) left their hideout in the Norwegian wilderness and skied several miles to Norsk Hydro's Vemork hydroelectric power plant.

All the men knew about their mission was the objective: Destroy Vemork's "heavy water" production capabilities.

Each man carried a cyanide capsule to take if they were captured and wore a British Army uniform so if they were killed and their bodies found, the Germans might spare the local civilians from reprisal killings.

Their mission would be one of the most successful in special-operations history, and it contributed to one of the Allies' most important goals in World War II: Preventing Nazi Germany from developing nuclear weapons.

The race for an atomic bomb

Within months of the discovery of nuclear fission on December 17, 1938, the military potential of nuclear power became clear, and the race for an atomic weapon was on.

In April 1939, Germany started its nuclear-bomb effort, known informally as the Uranverein, or "uranium club." It included some of the best scientists in the field, including the men who discovered nuclear fission and Nobel Prize-winner Werner Heisenberg.

During their research for a nuclear reactor, the scientists discovered that deuterium oxide, known commonly as "heavy water" because it has a heavier molecular weight than regular water, performed well as a moderator, enabling control over the fission process.

There was only one place in the world capable of producing heavy water on an industrial scale: Norsk Hydro's Vemork hydroelectric power plant in southern Norway. The plant's main purpose was to produce ammonia for nitrogen fertilizer; heavy water was actually a byproduct.

In January 1940, German officials asked to buy all of Norsk Hydro's heavy water stock and if it was possible to increase the plant's monthly output 10-fold to meet German demand.

This caught the attention of the French, who were experimenting with nuclear physics themselves and pursuing heavy water. Worried about German intentions, agents from the Deuxième Bureau, France's military-intelligence agency, secured all of Norsk Hydro's heavy water for France on March 9.

It was only a temporary setback for the Nazis. Exactly a month later, Germany invaded Norway and occupied it by early June. Vemork, now under German control, was forced to increase heavy-water production.

Operations Grouse and Freshman

The Allies, unaware of the German nuclear program's progress, were increasingly worried that Germany may be ahead in the race. Vemork's heavy-water production was known to be important to the program, and that alone was a good enough reason to take action against it.

Working with the Norwegian Resistance, the SOE created a plan for two teams to be dropped into Norway.

The first, codenamed Operation Grouse, was made up of four SOE-trained Norwegian commandos who would parachute into Norway, conduct reconnaissance, and secure a landing zone for a 34-man team of British commandos, codenamed Operation Freshman, who would land in two gliders and then assault the plant and destroy the 18 electrolysis cells that made heavy water.

On October 18, 1942, Grouse was launched. The team spent the next few weeks trekking to Freshman's designated landing site, reaching it on November 9. On November 19, Operation Freshman was launched.

But Freshman was a colossal failure. Mechanical difficulties and bad weather caused one of the bombers and the glider it was towing to crash, killing the flight crew and a number of commandos. The second glider's cable snapped when the bomber towing it aborted the mission, causing it to crash as well.

Survivors from both gliders were found by the Germans and executed as per Hitler's Commando Order. Forty-one men were lost, security at Vemork was increased, and the Grouse team was stranded and had to fend for itself.

Operation Gunnerside

Vemork was still a priority target for the Allies, and a new plan, with a stealthier approach, was developed.

A team of six Norwegian commandos would be dropped into Norway to link up with members of the Grouse team. They would infiltrate the plant, destroy the heavy-water production room with explosives, and escape into the night.

Codenamed Operation Gunnerside, the team parachuted into Norway on February 16, 1943, and linked up with the Grouse team on February 22. On the night of February 27, nine members from both teams set out for Vemork, with one member remaining behind to communicate with the British.

Upon arrival on the outskirts of the plant, they saw that the bridge, the only direct way into the complex, was heavily guarded.

The team had to descend a 328-foot cliff, cross a frozen river, then climb an almost 500-foot cliff before arriving at a fenced railway gate that led into the rear of the complex. They got there at 11:45 p.m. but had to wait for the guards to change shift, eventually cutting their way through the fence after midnight.

Once inside, the team split into two groups. Five commandos took covering positions outside the barracks, bridge, and main gate, while the other four entered the plant. Inside, they encountered only a Norwegian employee, who didn't resist or raise the alarm.

Explosives were set in the target room, which was in the basement. The team evacuated and waited for the explosion. Because the room was so far underground and the walls were so thick, there was hardly any noise when the bombs went off, allowing the whole team to escape before the Germans found out what had happened.

Aftermath

The operation was a resounding success. The commandos destroyed the electrolysis cells and over 500 kg of heavy water. They managed to escape without firing a single shot or taking any casualties.

The Germans repaired the damage by May, but subsequent Allied air raids prevented full-scale production. Eventually, the Germans ceased all production of heavy water and tried to move the remaining supply to Germany.

In a last act of sabotage, a Norwegian team led by one of the Gunnerside commandos sank the ferry transporting the remaining heavy water on February 20, 1944, although at the cost of 14 Norwegian civilians.

The operations helped foil Germany's nuclear ambitions, and the Nazis never built an atomic bomb or a nuclear reactor. Nazi Germany surrendered to the Allies in early May 1945, two months before the US's bigger and better-resourced Manhattan Project tested the first nuclear weapon on July 16, 1945.