Dawn of the Atomic Age, July 16, 1945: Trinity Test

The Trinity test was the dawn of the atomic age. (Image courtesy Los Alamos National Laboratories.)

Living History:

WASHINGTON, July 16, 2009 -- On July 16, 1945, at 5:29:45 a.m. Mountain War Time, the world's first atomic bomb exploded 100 feet over a portion of the southern New Mexico desert known as the Jomada del Muerto, the Journey of the Dead Man. As the orange and yellow fireball stretched up and spread, a second column, narrower than the first, rose and flattened into a mushroom shape, providing a visual image that has become imprinted as a symbol of power and awesome destruction. The world had never seen a nuclear explosion before, and estimates varied widely on how much energy would be released. The bomb exploded with a force of 21,000 tons of TNT, evaporating the tower on which it stood. Before the test, some scientists at Los Alamos privately had doubts that it would work at all.

The elaborate instrumentation surrounding the site was tested with an explosion of a large amount of conventional explosives on May 7. Preparations continued throughout May and June and were complete by the beginning of July. Three observation bunkers located 10,000 yards north, west, and south of the firing tower at ground zero would attempt to measure key aspects of the reaction. Specifically, scientists would try to determine the symmetry of the implosion and the amount of energy released. Additional measurements would be taken to determine damage estimates, and equipment would record the behavior of the fireball. The biggest concern was control of the radioactivity the test device would release. Not entirely content to trust favorable meteorological conditions to carry the radioactivity into the upper atmosphere, the Army stood ready to evacuate the people in surrounding areas.

On July 12, the plutonium core was taken to the test area in an Army sedan. The non-nuclear components left for the test site at 12:01 a.m., July 13. During the day, final assembly of the "Gadget" took place in the McDonald ranch house. By 5:00 p.m. on the July 15, the device had been assembled and hoisted atop the 100-foot firing tower. Leslie Groves, Vannevar Bush, James Conant, Ernest Lawrence, Thomas Farrell, James Chadwick, and others arrived in the test area, where it was pouring rain. Groves and Oppenheimer, standing at the S-10,000 control bunker, discussed what to do if the weather did not break in time for the scheduled 4:00 a.m. test.

Oppenheimer himself had bet $10 against George Kistiakowsky's entire month's pay that the bomb would not work at all. Meanwhile, Edward Teller was making everyone nervous by applying liberal amounts of sunscreen in the pre-dawn darkness and offering to pass it around. At 3:30, Groves and Oppenheimer pushed the time back to 5:30.

At 4:00, the rain stopped. Kistiakowsky and his team armed the device shortly after 5:00 and retreated to S-10,000. In accordance with his policy that each observe from different locations in case of an accident, Groves left Oppenheimer and joined Bush and Conant at base camp. Those in shelters heard the countdown over the public address system, while observers at base camp picked it up on an FM radio signal.

Seconds after the explosion came a huge blast wave and heat searing out across the desert. No one could see the radiation generated by the explosion, but they all knew it was there. The steel container "Jumbo," weighing over 200 tons and transported to the desert only to be eliminated from the test, was knocked ajar even though it stood half a mile from ground zero.

(From a U.S. Air Force report; information compiled from the U.S. Department of Energy's Office of History and Heritage Resources, and image courtesy Los Alamos National Laboratories.)

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