The date is 6 August 1945 and a nuclear bomb has just been detonated over Hiroshima in Japan. On hands and knees on his drawing room floor with his ear to the wall to overhear his neighbour's wireless, a 33-year-old classics-scholar-turned-printer from Birmingham called Michael Clapham is listening more intently than most.

He has good reason to. This bomb, as well as the subsequent Nagasaki bomb, which together killed hundreds of thousands of people and brought about the end of the Second World War, had dominated his life for the past four years. Clapham had, you see, helped to create it.

So how does a printer, who hadn’t even studied maths or science to undergraduate level, come to be involved in one of the most important scientific and military breakthroughs of the 20th century? The answer involves printing processes familiar to all in the trade, a great deal of ingenuity on the part of Clapham, a tin of Brasso and some leftover plates from an issue of Stitchcraft magazine.

It also involves a certain degree of chance. Had Clapham not been seconded to work as a night watchman at a munitions factory in Birmingham in 1941, and had he not happened to make the casual acquaintance of assistant research manager SS Smith there, history and the course of Clapham’s life could have been very different.

In his memoirs, written when he was 84 years old for family and friends, Clapham recalls the day he was summoned to Smith’s office.

"I was sitting at his desk on which was a newspaper, open at a page of pictures," he writes. "‘What,’ asked Smith, ‘do all the little dots in these pictures consist of?’"

Clapham patiently explained the photoengraving process to the researcher and he got a curious response. Could this process, asked Smith, be used to create a "very thin membrane with holes etched through it".

Clapham answered that this would be possible, in theory. However, no screen currently existed with holes as microscopic as Smith required, and Clapham believed it would be very expensive to create one.

But Smith was not put off, as Clapham soon discovered. 

From plates to tubes
"What the hell you know about tube alloys I’m damned if I know, but I’ve been told to second you full-time to this project as from today," Clapham’s manager informed him, packing him off to the top-secret and confusingly named ‘Tube Alloys Project’, with no explanation of what this mysterious metal membrane was needed for. Meanwhile, the only person capable of ruling a screen of the type needed was being withdrawn from active service and flown home.

The combination of these events made Clapham realise that whatever he was involved in was of "unimaginably high priority".

For most, then, it would have been a relief when weeks later the original photoengraving method proved unworkable. Yet Clapham was disappointed. Within his circle of family and friends, he was famous for his inventive and at times eccentric engineering escapades, and giving up was not his style.

So, back at his watchtower and over several sleepless nights, Clapham continued to give the problem some serious thought. "[There were] long and tedious nights, with frequent air raid alerts but only occasionally any aircraft within miles, [so I had] little to do but contemplate," wrote Clapham in his memoir. It was here that he had a eureka moment.

Instead of etching holes into metal, why not build a membrane around holes, Clapham realised. And he knew exactly how to do it.

With the help of a friend he first produced a 150-line screened negative using the black CMYK separation of the front cover of the previous month’s Stitchcraft magazine, which was lying around the print shop from a previous job. They then photographed this down to the smallest size they could, and masked off an area where the dots were most regular. Next, they coated some plates, printed the negatives and put them in a copper plating bath. The current did its work in depositing the sheet of metal and then it was just a question of separating this imaged copper sheet from the steel plate. Which was not easy. In fact it took Clapham and his colleague several hours to find a polish for the plate that would enable a clean lift of the copper sheet. This turned out to be Brasso.

"Smith gave it one look and took it over to his microscope," writes Clapham of the moment he showed his creation to his mysterious new friend. "‘Quick,’ said Smith, ‘tell me the story. These holes aren’t regular enough, of course, but this is the nearest thing anybody’s got to what’s needed. Is it repeatable? What’s the process? Could you use it to produce several thousands at first, and probably millions later?’"

The answers to these questions were to be uncovered over the following months by a team of scientists and engineers. Yet Clapham, despite his lack of scientific or engineering qualifications, remained at the centre of operations. This was because he had developed a knack for taking difficult concepts and explaining them in layman’s terms.

"‘You seem to be about the only person on friendly speaking terms with the scientists and the engineers,’" Clapham was told by one of his superiors, as he managed to unite the task force of scientists, mathematicians, expert engineers and two printing works .

Despite this pivotal position, however, Clapham still had no idea what it was he was working towards creating.  His only inkling was that it was some kind of filter for poison gas.

A headline glimpsed on a document – ‘Resistance to UF6’ – told him it was something more serious than even that. 

He looked up the obscure term in The Penguin Scientific Dictionary and did some personal research in the library. Suddenly "everything clicked into place", and Clapham realised that he was working on the world’s first atomic bomb.

A new use for perforations
What he had created was an efficient way of filtering out enough of the explosive elements of uranium from its non-explosive isotopes to make a bomb, something physicists had been wrestling with for some time. It was a leap forward in engineering that would make the atom bomb possible.

Today, we might assume that Clapham would pack his bags immediately to leave the project, horrified at the thought of creating such a destructive weapon. But that would be a misreading of history – Clapham’s actual reaction fitted the climate of the time.

Like many others after the event, Clapham was convinced that the bomb was a necessary evil – a conviction that he maintained until his death aged 90 in 2002. The war had stagnated and millions were dying on battlefields, sometimes for the sake of only yards of territory gain, and no one could see an end to the destruction and loss of life. The bomb was seen by many as the only way to end the carnage.

So Clapham did not cease work, but instead spent the next three years consumed by his mission. The printer from Birmingham became "liaison officer in the field of membrane production and development", a role that saw him advising the now much larger US development team on how to produce his membrane, and on the suitability of alternative production processes.

It was a role that catapulted Clapham far from his humble beginnings as manager of the Kynoch Press, of Birmingham, into a restrained James Bond character, with diplomatic bags containing top-secret samples and documents at his feet on flights to secret meetings.

"I had never been in an aeroplane other than for a 10-shilling hop in an open-cockpit biplane, so the prospect was wildly exciting," Clapham writes of the thrill of boarding a "great flying boat" to America, where he was wined and dined in a manner so lavish he found it hard to remember that there was a war on.

But Clapham never lost sight, amidst this excitement, of the great responsibility given to him, something that made him "feel older and more responsible than [his] 30 years justified".

It was with this sombre sense of responsibility that Clapham received the news, crouching on the floor to hear his neighbour’s wireless, that the bomb had finally been dropped on Hiroshima.

He realised fully his remarkable part in the events, calling himself "a craftsman, a rude mechanical, the inventor of a process", "a classics-educated printer gone wrong".

Yet this is not self deprecation, nor regret. To his death, Clapham was certain that the atomic bomb was a necessary evil and was proud of his part in it. For him, the bomb that his printing knowledge helped to create was the only answer and he used the last lines of his memoir to reiterate the point. 

"This fearful holocaust," he wrote, "was – it had to be – the end."

The life and times of Michael Clapham

1912 Michael John Sinclair Clapham is born
1930 Reads Classics at Cambridge but prefers printing on his Adana press to studying
1933 Begins working life as a printer’s apprentice with the Cambridge University Press, at 10 shillings a week
1941 Seconded full-time to work on the ‘Tube Alloys Project’ to develop the atomic bomb
1945 The bomb is dropped on Hiroshima and then Nagasaki, Japan
1959 Appointed chairman of Imperial Chemical Industries’ metals division, a position normally reserved "for chemists, physicists, engineers and metallurgists, not for Latin-speaking printers"
1972 Becomes chairman of The Confederation of British Industry
1974 Retires from the ICI board but continues as deputy chairman of Lloyds Bank, director of Grindlay’s Bank and president of the Institute of Printing
1973 Appointed KBE to become Sir Michael Clapham
2002 Dies aged 90