On the night of May 16, 1943, 19 Lancasters from 617 Squadron left their base at RAF Scampton, Lincolnshire, to attack western Germany’s great dams in the Ruhr Valley.
In the bomb bay of each Lancaster was a top-secret weapon, codenamed Upkeep, a huge cylindrical mine which, provided it was dropped with absolute precision, would destroy the dams.
The Dambusters Raids were to change the course of the Second World War, and Eyebrook Reservoir, near Corby, played a vital role in the operation.
The new weapon, which became known as the “bouncing bomb”, was revolutionary, and so was the way it had to be dropped.
Eyebrook estate manager Andy Miller said: “The concept was the brainchild of Professor Barnes Wallis.
“He worked out that the only way to breach the dams was to place a large charge against the dam wall, 30ft below the water.
“The combination of shockwaves from the explosion and the weight of the mass of water in the reservoir would cause the dam to give way.
“The next problem Wallis had to solve was how to put the charge in position.
“Each dam was heavily defended, including anti-torpedo nets across the reservoirs.
“Wallis’ solution was to design a weapon that would be spun backwards before release and then bounce across the surface of the water towards the dams.
“When dropped at the right distance and height, it would sink and explode at the required depth using a hydrostatic pistol.
“To carry out the raids the Royal Air Force formed a special squadron, made up from some of the best crews in Bomber Command, to be led by Wing Commander Guy Gibson.
“By March 24, 1943, the squadron was given its number, 617, but after May 17 it would always be known as The Dambusters.”
With less than seven weeks to the raid, the squadron had to practise every available day.
A number of reservoirs across England and Wales and stretches of coastline were used for low flying practice over water – and one of the practise sites was the Eyebrook Reservoir dam.
Over the next few weeks residents became used to the sound of Lancasters roaring overhead, skimming the treetops as they practised their low flying and bombing runs, day and night.
One resident of Caldecott was convinced that a late-night practise run by the Lancasters was a raid by German bombers, and took cover under his kitchen table.
The real reason for all the intense activity in the Welland valley only became apparent when the success of the raid was announced on the radio on May 17, 1943.
Mr Miller said: “Flying so low at a precise height and speed wasn’t going to be easy.
“The speed would be relatively simple to achieve, but there were no altimeters that were accurate at such a low level.
“By fitting spotlights in the nose and tail of their aircraft, set to converge at 60 feet beneath them, the crews had a method of getting the height spot-on.
“However, flying a huge four-engined bomber that low, over water, at night would take supreme airmanship.”
One of the Dambusters pilots, Flight Lieutenant Dave Shannon, later recalled that when it came to practising flying this low, Eyebrook Dam was much favoured.
The final piece in the jigsaw was how to release the weapon at the exact point to allow it to bounce across the surface of the water to arrive at the dam wall.
The solution was a simple sighting device with two vertical pointers that, when lined up with the towers of the dam, gave the correct release point.
Mr Miller said: “Corby and Northants District Water Company gave permission for scaffolding and netting structures to be erected on the Eyebrook Dam to represent the towers on the German dams and once again the crews made the short trip from their base in Lincolnshire to practise their bomb-aiming skills.”
They were put to use when the Mohne and Eder dams were breached, and the Sorpe damaged by 617 Squadron.
Mr Miller said: “It was a feat that fired the imagination of the nation, and continues to do so to this day, but it came at a price.
“Eight of the aircraft did not make it back.”
Last week the Battle of Britain Memorial Flight, made up of a Lancaster bomber, two Spitfires and two Tornado fighter jets, took part in a flypast at Eyebrook to mark the 70th anniversary of the Dambusters Raids.
One of the guests, Group Captain Steve Lloyd, deputy head of the RAF’s historical branch, organised the celebration.
He said: “The Air Force still uses the lake as part of our history programme and we bring our young airmen here. There are still significant lessons to be learned about special operations and leadership.”
In the fishing lodge at Eyebrook reservoir there is an information board showing copies of the correspondence between the Air Ministry and Corby and District Water Board requesting permission to use the reservoir for low-level practice.
Mr Miller said: “At either end of Eyebrook Dam is a commemorative plaque in remembrance of those who served with 617 Squadron, The Dambusters, a dignified and appropriate tribute to a remarkable event and even more remarkable people.”