Derring-do of The Dambusters

Their targets were the Moehne, Sorpe and Eder Dams near Cologne in Germany. Their weapon was the bouncing bomb, 7,000lb of explosives packed into a cylinder which was spun at 500 rpm to ensure it skipped across the water and into the dam walls.

To ensure success, the Lancaster crews had to release their payload 400 yards from the target while travelling at 240mph 60 feet above the water. It needed incredible skill and courage, but the squadron managed to breach two of the three dams.

"The most important consequence of this operation is the Ruhr industries will be deprived of a great deal of their industrial water for the coming summer," was the conclusion of the report written in the squadron's Operations Record Book for May 1943.

"The immediate effect of the floods from the two dams breached was to cause devastation and disruption throughout the valley of the Ruhr as far as Duisburg, and serious flooding below the Eder Dam at Kassel, and other places down the Wesser Valley."

The genius behind the bouncing bomb was Sir Barnes Neville Wallis. And this true giant of engineering has Yorkshire links.

Born in Derbyshire in 1887, Wallis was the son of a GP. He left school at 16 with no qualifications and began his career as a marine engineer, at one time working on the Isle of Wight.

In 1913 he moved to Vickers at Barrow-in-Furness to design airships. The R100 airship - the biggest yet designed - used Wallis's pioneering geodetic system to save weight, and was built at Howden.

Barnes Wallis' deputy chief engineer at the Airship Guarantee Co was Nevil Shute Norway. He flew the R100 airship to and from Canada, proving its reliability and range. It took three and a half days travelling at 75mph.

Later, he was to set up his own aircraft company, Airspeed, based on Piccadilly, York.

Wallis, however, was to move to Vickers' main factory in Surrey. There he turned his brilliant mind to aeroplane structures, and helped to design the Wellington bomber. He applied the geodetic structure of the airship to the plane, making it lighter and more efficient than its predecessors.

"The Wellington was one of the very, very few aircraft which was being built and in service throughout the war," recalled Peter Rix, chairman of the Barnes Wallis Memorial Trust based at the Yorkshire Air Museum, Elvington.

"The Spitfire was another one. The Lancaster didn't come in until about 1942; the Hurricane was in service through the war, but they stopped building it in 1944."

So even without the bouncing bomb, Barnes Wallis had made a massive contribution to the war effort with the Wellington. But he will always be remembered for his dam-busting idea.

"Barnes Wallis was not the first person to think of taking out the dams," said Mr Rix. "The thought had occurred in the Air Ministry in about 1937 or 38.

"They identified the dams as important targets but they couldn't see a way to destroy them.

"In about 1940 Barnes Wallis independently did a lot of research on dams, and thought that they could be destroyed."

It was not going to be an easy task. Hit the dam at the top, and it would not be breached; hit it lower down too far away from the wall and the water could absorb much of the impact of the blast.

"One of his first ideas was to drop a bomb from a great height into the water so it would go into the ground at the base of the dam and explode," Mr Rix said. But then he worked out that this would have required a ten-ton bomb being dropped from 40,000ft, and the RAF did not have any aircraft capable of such a feat.

Torpedos were no good, as the dams were most likely protected by nets which would catch them before impact.

Then Wallis remembered how Nelson had bounced cannon balls to extend their range and began to muse on that idea.

His early experiments involved catapulting marbles across a tub of water in his garden. By July 1942 he had tested the idea on an obsolete Welsh dam.

However, the following February Wallis was told to stop working on the dam raid. He offered to resign.

Then, in a turnaround almost as fast as the spinning bomb itself, a few days later he was informed the raid was on - and just 12 weeks away. That was all the time he had to perfect the bomb and assemble and train the aircrew. Wallis had to work around the clock.

"I had a terrible responsibility to make good on my claims," he wrote. "You cannot imagine what a horrible feeling that is when somebody has really called your bluff."

The raid, lit by a full moon, was led by Wing Commander Guy Gibson, who was awarded the Victoria Cross for his endeavours. He survived the raid - eight aircraft were lost and many crew died that night - only to be killed in action in 1944, aged 26.

Interestingly, the bouncing bombs in the film The Dambusters, in which Richard Todd played Gibson, were deliberately built wrongly. At the time the film came out, the design of the bomb remained a state secret.

Recently, some historians have queried what the dam raid accomplished. The Germans rebuilt the dams far more quickly than the Allies had expected. But Mr Rix believes it was a success on several levels.

It hit the Germans' steel industry as planned, weakening their war effort. And the project to rebuild the dams drew manpower away from building the Atlantic wall, to the benefit of the troops who landed on D-Day. Also the Nazis were forced to strengthen their anti-aircraft defences at the dams, diverting soldiers and weaponry from other fronts.

Mr Rix has talked to those who were around at the time of the raid. "They say the biggest impact it had was on morale. At that time, in 1943, things were not going that well generally.

"This was a huge morale booster."

Barnes Wallis had a mixed reaction to the dambusters' triumph. "He was horrified at the number of aircrew that had been lost. But I think he was quite pleased his idea had worked."

Wallis's creativity did not end with the war. He worked on swing wing jets and supersonic transport, nuclear submarines, radio telescopes and lightweight calipers for disabled people.

"He is one of the most wide-ranging visionaries in aeronautical engineering," said Mr Rix.

The Yorkshire Air Museum opened its permanent Barnes Wallis exhibition on the 50th anniversary of the dam raid. This week on the 60th anniversary - Friday - a new display will be unveiled. It will show how the operation was planned and how it unfolded.

Updated: 10:32 Monday, May 12, 2003