There's not many situations where you could conceivably find yourself relieved that a nuclear bomb HAD gone off. But that is exactly how Kenneth Bainbridge found himself feeling shortly after 05:29:21 on July the 16th 1945. He had just witnessed the first ever test detonation of a nuclear bomb. In the preceding few days, he had been entertaining a peculiar "personal nightmare" - if there had been a misfire, as the director of the test, it would have been his job to drive several miles over to the device and attempt to identify what had gone wrong with the potentially still armed weapon.
Obviously the importance of this exact instant in history cannot be overstated. It can be painted as so many things. I see it as the first time that our intellects allowed us to truly exceed the bounds of nature. In all other arenas of life we were still bound to nature in some way. We had learned to fly, but always had to land after a matter of hours. We had developed industrialised society, but it was fuelled by coal - essentially a more complex way of obtaining energy from the burning of wood, and ultimately from the energy of the sunlight that had grown those trees.
Now however, in the blink of an eye we had demonstrated mastery of power on a scale that previously the preserve of gods - to destroy entire cities at will. 6 KG of plutonium in the core of the bomb had unleashed an explosive force equivalent to 18600 tons of TNT, representing 3.1 million times the power on a kilo for kilo basis.
Considering that this was an event of such unparalleled importance in the history of our species, safety and secrecy were curiously lax. Some people had been worried that the bomb could set fire to the whole atmosphere, but the team were almost certain they had proved this was impossible. Even so, going ahead with the test still sounds like an outrageous risk to take, but on reflection isn't too different from the contemporary example of people being almost certain the Large Hadron Collider wouldn't create a black hole and destroy the planet. However, there were some more prosaic concerns to contend with, amongst them fears that a lightning strike could prematurely set off the bomb, or that the air force could accidentally conduct bombing practice on it (they had already overflown a target range and bombed the site of the scientist's dormitory).
Whilst the test was in about as isolated a place as it was possible to find in the continental United States, it was inevitable that people nearby would see evidence of the test, even if they didn't understand what they were seeing. The unearthly nature of the whole event is conveyed by a navy pilot flying nearby who thought he was seeing "the sun coming up in the south". A man and his son waiting at a train station 50 miles away thought a locomotive had exploded. A young woman took shelter under her bed with her grandmother, who was convinced they were witnessing the end of the world.
Whilst the bomb's power would later be viscerally demonstrated at Hiroshima and Nagasaki, the detonation over the desert of New Mexico created an interesting side effect. It left behind a crater filled with bottle-green glass, made from sand that had been fused by the unimaginable heat. This material relic of the birth of the nuclear age was christened "trinitite".