Trinity Test, July 16 1945
Eyewitness Report by Kenneth Greisen
July 21, 1945
To: Lt. Taylor
From: K. Greisen
Subject: Eye-witness account of Trinity shot
A group of us were lying on the ground just outside of base camp (10 miles from the charge), and received time signals over the radio, warning us when the shot would occur. I was personally nervous, for my group had prepared and installed the detonators, and if the shot turned out to be a dud, it might possibly be our fault. We were pretty sure we had done our job well, but there is always some chance of a slip.
At minus about 15 seconds I put my head close to the ground, turned to look away from the tower, and put up a shield between my head and the tower. I probably also closed my eyes briefly just before the shot. Suddenly I felt heat on the side of my head toward the tower, opened my eyes and saw a brilliant yellow-white light all around. The heat and light were as though the sun had just come out with unusual brilliance. About a second later I turned to look at the tower through the dark welding glass. A tremendous cloud of smoke was pouring upwards, some parts having brilliant red and yellow colors, like clouds at sunset. These parts kept folding over and over like dough in a mixing bowl. At this time I believe I exclaimed, "My god, it worked!" and felt a great relief.
When the intensity of the light had diminished, I put away the glass and looked toward the tower directly. At about this time I noticed a blue color surrounding the smoke cloud. Then someone shouted that we should observe the shock wave travelling along the ground. The appearance of this was a brightly lighted circular area, near the ground, slowly spreading out towards us. The color was yellow.
At what I presume was about 50 seconds after the shot, the ground shock and sound reached us almost simultaneously. The noise lasted for a long time, echoing back and forth from the hills. I noticed no sharp crack, but a rumbling sound as of thunder. After the brilliant optical display we had seen, the ground shock and noise were disappointing. No damage occurred, and we were not at all severely shaken.
Between the appearance of light and the arrival of the sound, there was loud cheering in the group around us. After the noise was over, we all went about congratulating each other and shaking hands. I believe we were all much more shaken up by the shot mentally than physically.
The permanence of the smoke cloud was one thing that surprised me. After the first rapid explosion, the lower part of the cloud seemed to assume a fixed shape and to remain hanging motionless in the air. The upper part meanwhile continued to rise, so that after a few minutes it was at least five miles high. It slowly assumed a zigzag shape because of the changing wind velocity at different altitudes. The smoke had pierced a cloud early in its ascent, and seemed to be completely unaffected by the cloud.