An Explosive Ending
Just before midnight on February 27, 1943, the commandos crossed the ravine during a schedule guard change. They crept into the building undetected. According to Ronneberg, two of them began laying the charges. The team knew that if anything happened to threaten the mission, each member had to act on their own. Three others broke a window to get into a room only to find their two comrades at work. The group’s target was a battery of 18 cells which was the last stage in the production of heavy water.
The charges weighed less than 10 pounds; there were four of them with two-minute fuses. Ronneberg elected to cut the fuses to 30 seconds and lit them once everyone had run out of the room. While the blast was thunderous within the room, the guards on the outside barely noticed. They assumed the noise came from the combustion equipment which occasionally made a muffled sound. According to the lookout team, only one guard emerged, and after walking around for a short while, he returned to his station.
Aftermath
Operation Gunnerside was a total success. All 10 members escaped (despite pursuit by a search party of 3,000 Germans) and, according to Ronneberg, it took just three hours to get from the scene of the bombing to the mountainside where their skis were waiting. Although Vemork suffered relatively minimal damage, the commandos destroyed 1,000 pounds of heavy water along with the equipment needed to create it.
Gunnerside halted production of heavy water for several months, but in April 1943, the SOE knew the Nazis would soon be capable of making the ingredient again. They couldn’t launch another commando raid due to heightened security, but a series of bombing raids in November 1943 and the sinking of the SF Hydro (used to transport heavy water) ended German hopes of producing and transporting heavy water.
According to historians, the German nuclear program in World War II was a long way from being capable of producing an effective bomb. However, the Allies didn’t know this, and the bravery of the 10 men in Operation Gunnerside cannot be understated. The SOE later said that the mission was the most successful act of sabotage of the entire war. Every member of the group received war honors, with Ronneberg and two others in receipt of a Distinguished Service Order.
The exploits of these men were even turned into movies; a Norwegian film in 1948 and a better-known 1965 release called The Heroes of Telemark with Kirk Douglas and Richard Harris playing starring roles. Stromsheim lived to the ripe old age of 101 and died in 2012. Ronneberg is the last surviving member of Operation Gunnerside; he currently resides in Alesund, Norway.