Detonation had been planned for 0400 on 16 July but was delayed for over an hour due to rain and lightning. After breakfast of powdered eggs, French Toast, and coffee served at 0345, the Army party reached the South 10,000 bunker at 0508. Bainbridge unlocked the master switches and Joe McKibben activated the timing switches that began the final 20-minute countdown to 05:09:45.
The countdown was broadcast so that it could be heard at base camp through the loudspeaker system. Also heard through the loudspeakers were the national anthem and a Tchaikovsky composition as the countdown crossed frequencies with a Voice of America broadcast in California.
A few minutes before detonation, a flare was launched and a siren wailed at base camp. Then came a two-minute warning, followed by a one-minute warning. Groves, next to Vannevar Bush at base camp, thought about what he would do if they threw the switch and nothing happened. At the South 10,000 bunker, Oppenheimer, barely breathing, gripped a post to steady himself. At T-minus 45 seconds, Joe McKibben threw the switch that started the final automatic timing sequence.
In the intense breathless quiet, Sam Allison’s voice counted down, “5…4…3…2…1. NOW.” Without a sound at exactly 05:29:45 Mountain War Time on 16 July 1945, mankind dove into the unknown and emerged in the Atomic Age. The device exploded with a yield of 21 kilotons, or 21,000 tons of TNT. There was a flash of light, followed by the shock wave and the roar of the explosion. It was as though the sun was shining as the first flash lasted more than ten seconds, followed by an enormous ball of fire for another ten seconds, then the billow of smoke and a second flash that lasted around four seconds.
For many facing away from the blast, the surrounding hills shimmered in the bright light and then began to fade after a few seconds. After ten seconds it turned into a huge fireball rising slowly into the sky. A mushroom cloud grew, then stopped, followed by a second mushroom cloud that grew from the first. Then came the blast wave and the heat. This was followed by the actual sound of the explosion as the sound wave raced across the landscape, which was followed by a long rumble. Captain Bush, outside the bunker, faced away crouching. It was so bright he touched his eyelids to make sure they were closed. When he turned, he was knocked over by the shock wave.
To some, the most startling feature was the intense light as “the sun rose twice” when the real sun rose shortly after the explosion. For others it was the intense heat.
Enrico Fermi at base camp reported the shock wave took 40 seconds to reach his location. He had torn a piece of paper into bits and tossed them into the air to measure the shock wave.
The 21-kiloton explosion vaporized the 100-foot steel tower on which the Gadget has rested, depressed the ground into a crater about 8 feet deep and 800 yards across, raised a cloud of dust and dirt 35,000 feet high, and created the green glassy substance that came to be known as Trinitite. The desert sand was scooped up into the fireball, the heat melting the grains and causing it to behave like raindrops falling back to earth. The molten drops collected on the hot ground and cooled to form the layer of Trinitite that covered the crater. The cushion of air under the tower limited the size of the crater, which was characterized as more of a depression than crater. One of the tower’s footings sunk in concrete is still visible. Jumbo’s tower 800 yards away was destroyed and twisted completely out of shape. An instrument tower ½ mile away was ripped from its foundation and mangled. The instrumentation bunker at North 1,000 was damaged. Vegetation out to 1,200 feet was gone.
The flash of light was seen 180 miles away and the explosion was heard 100 miles away. The shock wave did no damage in Socorro, but broke windows in Silver City 120 miles away. Gallup, 150 miles away, was hit with a thunderclap and caused officials to think an ammunition bunker at the nearby Fort Wingate Depot had exploded.
Monitors and scientists detected dust and radioactive material up to 120 miles away. There were pockets of higher radioactivity, but no concentrations that required evacuations. Observers positioned up to 200 miles away reported no damage.
The B-29s held off due to the storm did not see the blast but rather saw the blast reflected on the clouds. After a few moments of silence, J. Robert Oppenheimer at the South 10,000 simply remarked, “it worked.”