The quest to discover whether an amateur was up to the task presented the US Army with the profoundly bizarre challenge of trying to find people with exactly the right lack of qualifications, recalls Bob Selden, who eventually became the other half of the two-man project. (Another early participant, David Pipkorn, soon left.) Both men had physics PhDs - the hypothetical Nth country would have access to those, it was assumed - but they had no nuclear expertise, let alone access to secret research.

"It's a very strange story," says Selden, then a lowly 28-year-old soldier drafted into the army and wondering how to put his talents to use, when he received a message that Edward Teller, the father of the hydrogen bomb and the grumpy commanding figure in the US atomic programme, wanted to see him. "I went to DC and we spent an evening together. But he began to question me in great detail about the physics of making a nuclear weapon, and I didn't know anything. As the evening wore on, I knew less and less. I went away very, very discouraged. Two days later a call comes through: they want you to come to Livermore."