They were the men who took on the might of a mountain so that the entire nation could switch on the kettle after Coronation Street.

Nicknamed the Tunnel Tigers, the 4,000 strong army of danger workers were drafted in to Argyll to hand drill their way into the bowels of Ben Cruachan.

Deep inside what is now known as Scotland's hollow mountain, a ground-breaking hydro electric power station was built with only a man made dam visible on the hill outside.

The mammoth task, which was six years at the construction stage, saw 36 of the brave workforce lose their lives in the quest to achieve one of the most remarkable feats of engineering design the world has ever seen.

The Cruachan Power Station, which the power to top up the National Grid is stored, is celebrating its 50th birthday today, having been opened by the Queen.

It ensures there is also enough power at times of peak demand on the grid when the nation's kettles are all switched on at once after popular TV programmes such as Coronation Street, Eastenders and major sporting events finish.

To mark the anniversary of the station's completion five of the tunnel tigers, now in their seventies, walked through the hand-drilled caverns and hiking up the inside of the 4,000ft high mountain, via a flight after flight of stairs in the vertical shaft space which leads to the power control room.

They also took a trip up to the hilltop dam above Loch Awe, which is an intergral part of the ground breaking hydro power scheme.

The blunt reality of the human price paid for this magnificent engineering feat hit home on the very first port of the tour, when the group stopped at a small stone memorial to workmates who lost their lives.

Irishman John O'Donnell, who worked in the construction project, was emotional as he placed a small basket of flowers on the monument.

He said: "My next door neighbour Hugh Rogers - I grew up with him - was working at Cruachan, when there

was another death. He said, there is eleven gone now, I wonder who will be the twelfth?

"He was the next. He died when 600ft of steel pipe, full of concrete, came down through the shaft."

Mr O'Donnell, 76, added: "Thirty six men died in the construction phase but many, many, many more died with illness afterwards, including my brother, who died from emphysema.

"There was no health and safety then, that is the reason I am wearing a hearing aid now, and we never had anything, no goggles, no oil skins, just a helmet.

"The noise was unbelievable, for the first fortnight I was stone deaf, I couldn't talk, it was just sign language. We used sign language to tell people to get out of the way.

"You got stones overhanging and some of them could weigh over a tonne, everybody looked out for me, everybody

saved my life, everybody saved everybody's lives.

"You couldn't talk,when one guy was in danger I broke the air bag going to his drill machine to get his attention and

he got out of the way."

He added: "Nobody was ever born in a tunnel, you had to learn. It was absolutely amazing that more workers weren't

killed, because we were working with electrical detonators and we were drilling with water because we couldn't dry drill. I would imagine over 100 have died later from emphysema."

"We were all mad, you had to be. I would never go down today."

Mr O'Donnell was part of the team who drilled the first holes into the hard granite rock face. They drilled out a tunnel just over a mile into the hillside, before a team began creating a vertical shaft up the mountain.

Hugh Finlay, Generation Director at ScottishPower, which runs the site, said; "It was a prodigiously complex feat of engineering to design a power station buried deep inside a mountain, and it was a herculean task to construct it.

The genius of Sir Edward MacColl’s initial design, coupled with the skill and determination over six years from the 4,000 strong workforce,

ensured that Cruachan Power Station was built to last. It is as important today as it was 50 years ago.

"The station has also been a major presence in the local community. Generations of families have worked there over the years, and Cruachan

has only been a success because of their efforts."