JOACHIM RONNEBERG'S story is the stuff of legend, immortalised on the silver screen and forever remembered as an act of heroism that changed the course of history.

The objective of his mission was simple, yet fraught with danger - to infiltrate the most heavily-guarded structure in occupied Europe and shatter the Nazi atomic bomb project.

Failure, according to Allied scientists who were frantically working to produce their own A-bomb, would have almost certainly handed victory to Germany.

Not only were the Allies far behind in their work, all available stocks of heavy water - used to control nuclear fission - were produced at Rjukan, Telemark, in the south of German-occupied Norway.

Perched hundreds of feet above the ground, the Norsk Hydro factory was considered impregnable. Still, it remained imperative that it was taken out.

After earlier operations had ended in tragedy, a fourth - code-named Gunnerside - was put into action.

On February 16, 1943, six British-trained Norwegian commandoes were dropped, in blizzard conditions, on the treacherous Hardanger plateau.

They were met by resistance fighters from the failed Operation Grouse, who had withdrawn to the plateau months earlier and were surviving by hunting wild reindeer, and skiing through the freezing lands to dodge German patrols.

By February 27, they were ready. Led by 2nd Lieutenant Ronneberg, the saboteurs climbed down the gorge, crossed the river and scaled the rock face leading to Norsk Hydro.

After completing the perilous journey, avoiding Nazi eyes, they cut through the perimeter gates with wire clippers.

A cover party took up position as the saboteurs advanced, ultimately placing their short-fuse explosives on the crucial heavy water container. The rest, as they say, is history.

Splitting into two groups, the commandoes' lives remained at risk as they made their escape - some remaining in Norway and others, including the leader, fleeing their German hunters on skis to the safety of neutral Sweden.

"We were extremely lucky. Everything went our way," said Mr Ronneberg, now 84, as he visited the Hydro Polymers plant in Newton Aycliffe, County Durham, yesterday.

"It took us 18 days to reach Sweden. When we got there, we had to report as refugees because the Swedes had not yet decided who was going to win the war. Eventually, we made contact with the British Army in Stockholm."

Their exploits spawned the Heroes of Telemark film, starring Kirk Douglas and Richard Harris, but Mr Ronneberg plays down the heroism of his men.

"We looked upon it as an ordinary raid. We didn't know what they used heavy water for at all," he said.

"After the atom bombs in Japan, only then did we know what we had taken part in. We read all of these newspaper headlines, The Norwegian Men Who Saved The World.

"They have made films and it is much talked about, but I think that is only because we still have the threat of the atom bomb, even now."

Mr Ronneberg's visit coincided with Norwegian-owned Hydro's centenary and the 60th anniversary of VE Day. The plant stands on the site of the former Royal Ordnance Factory and Mr Ronneberg took time to view a sculpture commemorating the Aycliffe Angels, who worked in munitions.

"It is very interesting to see. This is so important for future generations, to remind them of the past and to prevent such a war ever happening again."

Mr Ronneberg also met Vi Hudson, who made munitions boxes during the war and knew his colleagues through their time training at Catterick, in North Yorkshire.

"I'm still in a trance. I've longed to meet up with them again, but I could never do it," she said.