Even after 52 years I can still vividly recall Dr Barnes Wallis, inventor of the ‘skipping’ bombs which breached the Ruhr dams, standing at the front door of his home: the shock of white hair, knobbly knees in khaki shorts, responding curtly: ‘Impossible, I don’t give interviews.’

That was in 1967. An Australian, I was working for Beaverbrook’s Sunday Express, in Fleet Street, under editor John Junor, and turned up unannounced at Wallis’s house in Effingham village, Surrey, hoping for that interview.

It will be 76 years on May 16-17 since the Dambuster raids on the Ruhr dams with Wallis’s remarkable ‘skipping’ bombs. The attack by 19 RAF Lancasters of 617 Squadron breached the Mohne and Eder dams, sending millions of tonnes of water 80km through the Ruhr Valley killing almost 1,300 people, and costing the lives of 53 aircrew.

Militarily, the raid was a failure: disruption to German war production was minimal and the Ruhr Valley water supply was back to original levels within two months. But it was a significant boost to British morale in those dark days of 1943.

Perhaps it was my disappointment and blurting of ‘a privilege to meet you’ that made the difference: Wallis told me to be at his office at the British Aircraft Corporation, Weybridge, the following morning. I had researched his career:

How his R-100 airship made an Atlantic crossing from Britain to Canada and back in 1930; his geodetic Wellesley bomber and its 1938 world record flight non-stop from Egypt to Australia, the Wellington which, though shot to ribbons, brought its crews back alive time and again in the Second World War; blockbuster bombs which sank the German battleship Tirpitz and wrecked the U-boat pens and the V3 rocket pads. Plans also for high-powered submarines carrying cargoes at speeds up to four times as fast as surface vessels in all weathers across the world.

I knew, too, that he had been working for several years on a new, hypersonic aircraft which could fly from London to Australia in 90 minutes. When I put that to him, he would only say, ‘Why not?…Why not?’

He wouldn’t elaborate on those proposals, but said: ‘If the British government turn down my latest proposals – which I have not yet put to them – I will certainly go to America. Whether the Americans employ me or not, I don’t care as long as my proposals are taken up. I am not out to make a fortune – it’s the fun of the work.’

First, we watched a colour movie of his tail-less, swing-wing aircraft, the Swallow, a model in steel and balsa. The British government had rejected that ten years earlier, only to buy it back as the F-111 fighter bomber. ‘My dear fellow, the Swallow was the most beautiful thing you ever saw,’ he told me. ‘In ten years we spent £1,750,000 on it and were ready to build a manned aircraft. It could have been flying two years ago.’

He was told to take his findings to the US and place them before American aeronautics experts with the hope that he would be given a grant under the Mutual Weapons Development Program. But he recalled: ‘The Americans said, “It’s much too good to develop in Britain – we will develop it ourselves.” Now it’s coming back in the shape of the F-111. But it’s not as good as we would have done – they didn’t know how to get along without the tail.’

Was he bitter about the Swallow affair?

He responded almost fiercely: ‘It’s the fight that matters, whether you win or lose is of no consequence. If you lose, you start again. It’s probably a damn lucky thing… I’d better not go on.’

Was there – as often been said – a vehement anti-Wallis clique in Whitehall?

‘I don’t know and I don’t care. I suppose I am too outspoken.’

He still remembered – ‘Indeed, I do’– that morning in May 1943 when he waited for the 617 Squadron Lancaster crews to come back from the Ruhr dams – and realised that 53 would never return.

‘To me, it was a great tragedy, not a triumph. But I don’t allow it to prey on my mind. I have too much sense for that.’

He gave the £10,000 government award for the invention of the bomb to his old school Christ’s Hospital for a fund to educate the orphans of the RAF men who died, with the biblical text of Samuel in his mind: ‘Is this not the blood of the men that went in jeopardy of their lives?’.

What did he see as his greatest achievement?

‘Having nineteen grandchildren.’ And then: ‘I don’t see that I have ever achieved anything great. It would be a damn conceited attitude to take, and I am not a conceited man. Mind you, I am helped by an extremely competent staff and being a fellow of the Royal Society gives you the freedom of the scientific world. You can put the odd question to the greatest experts in the world.’

‘And my wife looks after me – you must take my little missus into account.’

Many of his triumphs, he agreed, came only after a long struggle. ‘Struggle is the sauce of life, my dear boy. I often ask modern headmasters whether they agree that a certain amount of struggle is necessary to achieve the full development of character.’

And then:

‘Character is developed by endurance and constantly facing and beating hardship. Once children walked five miles to school. Now they are collected by bus and education is poured down their necks. Where is the struggle to form the first degree of character?’

‘I do not use the National Health Service – of course I pay into it – because I was born in Victoria’s reign and was taught to be independent. People were proud to stand on their own feet. Now they expect everything to be provided by the State. There appears to be a profound change in the national character. I say “appears” because I don’t know.’

‘But would these fellows with their long hair and beastly shoes join up and fight as bravely as their fathers? Probably they would. My dear fellow, they must be braver than you or me to go around like that. But is it because life is so dull that they must do something. I wish I could read the mind of England today.’

He added:

‘I shall go on working as long as I possibly can. I will be 80 in September, but I have the heart and lungs of a man of 50. I garden hard every night and I can still walk up a mountain in the Lakes District. I do not smoke or drink and eat as little meat as possible.’

Barnes Wallis was knighted a year after we spoke and died at 92 in 1979.