'We did what we had to do': The true story of World War Two's Dambusters raid

In May 1943, a specially formed RAF squadron embarked on a daring moonlit mission – but its success came with a heavy cost. In 1976, the BBC spoke to one of the airmen who made it home alive.

Throughout the month of April 1943, Jack Buckley practised low-level night-flying and navigation for a top-secret mission as part of Royal Air Force 617 Squadron. Operation Chastise's security was so tight that no one in the hastily formed squadron – made up of 133 airmen from the UK, US, Australia, Canada and New Zealand – actually knew what they were training for. 

There was plenty of speculation, "but no one was near the truth," Buckley recalled to the BBC when he was interviewed in 1976 at RAF Scampton in Lincolnshire. "Someone had the bright idea that we might be dropping tanks in the desert, and there were other far-flung ideas [such as] going against the Tirpitz [German battleship]." Ultimately, the 617 Squadron would become known by the name of the audacious and dangerous mission they were about to embark on – the Dambusters.

At 21:28 on 16 May 1943, 82 years ago this week, the first of 19 specially modified Lancaster bombers took off for a precision raid that aimed to cripple the Third Reich's war machine. Their target was three huge dams at Möhne, Eder and Sorpe in German's military-industrial heartland.

The dams were supplying water and hydro-electric power to the surrounding German factories that were manufacturing armaments. It was thought that if the dams could be destroyed, the resulting flooding would cause catastrophic damage to the Nazis' war production and morale. A plan to attack the dams had been raised earlier in the war, but, given that the flight route was heavily defended and no plane at the time could carry a bomb large enough to destroy them, the task had been considered impossible. But the aircraft that took off in May 1943 were carrying a potent new weapon – the bouncing bomb.

Codenamed Upkeep, the purpose-built explosives had been invented by aircraft engineer Dr Barnes Wallis. Wallis had realised that smaller bombs could have the required effect if they were detonated at the right place, underwater near the base of the dam. He designed a barrel-shaped bomb that could skip across the surface of water the same way a stone does when it is skimmed. This enabled the explosives to by the protective underwater nets which were placed around the dams to prevent torpedoes.

But for the bombs to work, they had to be dropped from the exact altitude and the right speed. A plane would need to fly low across the water at a height of just 60ft (18m) and a speed of 232mph (373kmh). This would enable the bomb to bounce until it hit the dam, where its backspin would cause it to run down the side of the dam until it reached a depth of 30ft (9m) and explode. Wallis had modelled this trajectory by skimming marbles across a bathtub filled with water in his back garden.

The weapons were still too big to fit into a Lancaster's bomb bay, so aircraft were modified so that bombs could be carried underneath, and much of the planes' armour had to be removed so that they would be light enough to fly.

The 617 Squadron bombers set off in three waves, each targeting a different dam. Buckley was in the first wave of nine planes led by the squadron's 24-year-old Wing Commander Guy Gibson. As the rear gunner in a bomber piloted by Dave Shannon, Buckley told the BBC that he ed feeling "glad that we were on our way" as the plane took off from the runway. "We set course for the enemy coast. It was a full moon, it was almost like daylight," he said.

The dangerous mission required exceptional flying skill and precision navigation. To avoid radar, the Lancasters needed to fly at low altitudes on flight routes that weaved in and out of positions where there were known anti-aircraft guns. At least three planes were shot down when they strayed off their routes, while two others crashed because they were flying low enough to hit high-voltage power lines.

Buckley's Lancaster was one of the ones that made it to the rendezvous over the 2,000ft-long (650m) Möhne Dam. Gibson decided to take the bombing run, while the others circled, waiting for their chance. The Möhne approach was especially hazardous. Surrounded by tree-covered hills, the aircrew were exposed to flak from gunners in the towers as they dropped low across the surface of the water. When it came to Buckley's bomber's turn, four other Lancasters had already dropped their bombs, and one plane had crashed after being hit by enemy fire and the blast of its own bouncing bomb. But the Möhne Dam was still standing.

Because the Lancaster's altimeter was not accurate enough, spotlights had been installed at each end of the aircraft to tell the airmen when they were at the right height. "We circled, we had to be 60ft exactly, we had a spotlight in the nose of the aircraft and a spotlight in the tail and they converged at exactly 60ft," said Buckley. "Number five was [pilot David] Maltby, well, he dropped his weapon successfully. We were just on the run in and Gibson called us off – the dam was gone."