In 1945, I was a member of a super-secret Army intelligence unit attached to the Manhattan Project, which produced the atomic bomb. We were sent to a desert camp called Trinity, northwest of Alamogordo, New Mexico; our assignment was to cover the area within a hundred-mile radius of zero point so that we could remove residents quickly if the mushroom cloud blew toward them spewing radioactive dust.

The blast was scheduled for July 16, 1945, at 4:00 A.M. A fellow agent, Harold Jensen, and I drew Socorro, a little town northwest of ground zero, as our vantage point. A soaking thunderstorm was in progress as we parked our car outside town to avoid attracting attention at that early hour.

We waited until 4:50. Then until 5:00. Strangely, nothing happened even after the storm had abated. Had there been a postponement? We drove into Socorro to call from a pay phone in the lobby of a small hotel—we had been given codes so that we would not reveal the secret—but there was no response from the operator. The phone was dead.

We knew that all telephone communications from Los Alamos to the desert test site went through Socorro, and it was vital that scientists and engineers in Los Alamos and Santa Fe communicate with authorities in the desert who were preparing the test. We had to find out what had happened to disrupt communications.

We tracked down the telephone exchange by following overhead cables. The switchboard turned out to be in a private home, as were many in small towns back then. From the porch, we could see scores of lights flickering, indicating that officials were frantically trying to get through.

Unaware of her key role in the momentous test, the operator was sound asleep on a cot beside the switchboard. I pounded on the door. She came out rubbing her eyes. I nodded toward the switchboard, and she sprang to work, putting through the calls.

That did it.

Jensen and I returned to our outpost and sat on the front fender of the car to watch the show. At 5:30, the detonation took place: no sound at first, just a giant, bright yellow fireball like a super-sun that hurt the eyes. In a few moments came the sound of a drummer striking a huge drum, but we felt no concussion or strong wind.

Like everyone else, Jensen and I kept the explosion secret until August 6, 1945, when President Truman announced “the most terrible destructive force in history.”