Jeremy Bernstein’s Memoir: At Los Alamos in the LRB.
He advised me to face away from the explosion and count to ten. I was also given some very dark glass to put over my own glasses. Even the reflection from the bunker walls could damage your eyes. I don’t know how far away from the explosion we were but we were close enough to see the 700-foot tower that had the bomb on top of it. I noticed a hill behind the tower with a grove of Joshua trees. They looked as if they were praying. A loudspeaker counted out the minutes until the explosion and then counted down the last sixty seconds. I had turned my back and covered my eyes with the dark glass but the bright flash still made me shut them. I counted to ten and then turned round.
The horizon in front of me was in turmoil. In the centre was a livid red-orange cloud. The hugeness of it was what impressed me. I had had no idea of the sheer scale of a nuclear explosion. Peaslee had prepared me for the next step. I felt a sharp and slightly painful click in my ears. This was the supersonic shock wave. At Hiroshima it produced a wind stronger than any known typhoon: it knocked over the kerosene cookers the Japanese used to make breakfast and caused most of the fires at Hiroshima. Then came the sound: a sort of rolling thunder. The cloud had turned purple and black and hung in the air like a radioactive cobra about to strike. There was talk of taking cover, but it didn’t move in our direction. I stood there mute. We went back to the dormitory to get a little more sleep.