Eyewitness Report by Enrico Fermi

Observations During the Explosion on July 16, 1945

“On the morning of July 16, I was stationed at the Base Camp at Trinity, about ten miles from the explosion site.

The explosion occurred at about 5:30 A.M. I had my face protected by a large board with a piece of dark welding glass inserted. My first impression of the blast was the intense flash of light and a heat sensation on my body’s exposed parts. Although I did not look directly toward the object, I had the impression that suddenly the countryside became brighter than in full daylight. I subsequently looked toward the explosion through the dark glass and saw something like a conglomeration of flames that promptly started rising. After a few seconds, the rising flames lost their brightness and appeared as a massive pillar of smoke with an expanded head like a gigantic mushroom that multiplied beyond the clouds, probably 30,000 feet. After reaching its full height, the smoke stayed stationary until the wind started dissipating it.

About 40 seconds after the explosion, the air blast reached me. I tried to estimate its strength by dropping from about six feet small pieces of paper before, during, and after the passage of the blast wave. Since there was no wind at the time, I could observe very distinctly and measure the displacement of the pieces of paper that were falling while the blast was passing. The shift was about 2 1/2 meters, which, at the time, I estimated to correspond to the explosion that would be produced by ten thousand tons of T.N.T.”

Source: U.S. National Archives, Record Group 227, OSRD-S1 Committee, Box 82, folder 6, “Trinity.” Transcription: Thank you, Gene Dannen, for transcribing this document.