Manhattan Project: The Trinity Test, July 16, 1945

Time Periods

1890s-1939:
Atomic Discoveries

1939-1942:
Early
Government Support

1942:
Difficult
Choices

1942-1944:
The Uranium
Path to
the Bomb

1942-1944:
The Plutonium
Path to
the Bomb

1942-1945:
Bringing It All Together

1945:
Dawn of the
Atomic Era

1945-present:
Postscript --
The Nuclear Age

THE TRINITY TEST
(Trinity Test Site, July 16, 1945)
Events > Dawn of the Atomic Era, 1945

Until the atomic bomb could be tested, doubt would remain about its effectiveness. The world had never seen a nuclear explosion before, and estimates varied widely on how much energy would be released. Some scientists at Los Alamos continued privately to have doubts that it would work at all. There was only enough weapons-grade uranium available for one bomb, and confidence in the gun-type design was high, so on July 14, 1945, most of the uranium bomb ("Little Boy") began its trip westward to the Pacific without its design having ever been fully tested. A test of the plutonium bomb seemed vital, however, both to confirm its novel implosion design and to gather data on nuclear explosions in general. Several plutonium bombs were now "in the pipeline" and would be available over the next few weeks and months. It was therefore decided to test one of these.

Robert Oppenheimer chose to name this the "Trinity" test, a name inspired by the poems of John Donne. The site chosen was a remote corner on the Alamagordo Bombing Range known as the "Jornada del Muerto," or "Journey of Death," 210 miles south of Los Alamos. 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 (right) 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 (left). The non-nuclear components left for the test site at 12:01 a.m., Friday the 13th. During the day on the 13th, final assembly of the "Gadget" (as it was nicknamed) took place in the McDonald ranch house. By 5:00 p.m. on the 15th, 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. To break the tension, Fermi began offering anyone listening a wager on "whether or not the bomb would ignite the atmosphere, and if so, whether it would merely destroy New Mexico or destroy the world." Oppenheimer himself had bet ten dollars 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.

During the final seconds, most observers laid down on the ground with their feet facing the Trinity site and simply waited. As the countdown approached one minute, Isidore Rabi said to the man lying next to him, Kenneth Griesen, "Aren't you nervous?" "Nope" was Griesen's reply. As Groves later wrote, "As I lay there in the final seconds, I thought only of what I would do if the countdown got to zero and nothing happened." Conant said he never knew seconds could be so long. As the countdown reached 10 seconds, Griesen suddenly blurted out to his neighbor Rabi, "Now I'm scared." Three, two, one, and Sam Allison cried out, "Now!"

At precisely 5:30 a.m. on Monday, July 16, 1945, the nuclear age began. While Manhattan Project staff members watched anxiously, the device exploded over the New Mexico desert, vaporizing the tower and turning the asphalt around the base of the tower to green sand. 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. As the orange and yellow fireball stretched up and spread, a second column, narrower than the first, rose and flattened into a mushroom shape, thus providing the atomic age with a visual image that has become imprinted on the human consciousness as a symbol of power and awesome destruction.

The most common immediate reactions to the explosion were surprise, joy, and relief. Lawrence was stepping from his car when, in his words, everything went "from darkness to brilliant sunshine in an instant"; he was "momentarily stunned by the surprise." (Click here to read Lawrence's thoughts on the Trinity test.) A military man was heard to exclaim, "The long-hairs have let it get away from them!" Hans Bethe , who had been looking directly at the explosion, was completely blinded for almost half a minute. Norris Bradbury reported that "the atom bomb did not fit into any preconceptions possessed by anybody." The blast wave knocked Kistiakowsky (who was over five miles away) to the ground. He quickly scrambled to his feet and slapped Oppenheimer on the back, saying, "Oppie, you owe me ten dollars." The physicist Victor Weisskopf reported that "our first feeling was one of elation." The word Isidor Rabi used was "jubilant." Within minutes, Rabi was passing around a bottle of whiskey. At base camp, Bush, Conant, and Groves shook hands. Rabi reported watching Oppenheimer arrive at base camp after the test:

You've seen pictures of Robert's hat. And he came to where we were in the headquarters, so to speak. And his walk was like "High Noon" -- I think it's the best I could describe it -- this kind of strut. He'd done it.

When they met, Groves said to Oppenheimer, "I am proud of you." Groves's assistant, Thomas Farrell, remarked to his boss that "the war is over," to which Groves replied, "Yes, after we drop two bombs on Japan." (Click here to read Groves's observations of the Trinity test [pdf].) Probably the most mundane response of all was Fermi's: he had calculated ahead of time how far the blast wave might displace small pieces of paper released into it. About 40 seconds after the explosion, Fermi stood, sprinkled his pre-prepared slips of paper into the atomic wind, and estimated from their deflection that the test had released energy equivalent to 10,000 tons of TNT. The actual result as it was finally calculated -- 21,000 tons (21 kilotons) -- was more than twice what Fermi had estimated with this experiment and four times as much as had been predicted by most at Los Alamos.

Soon shock and euphoria gave way to more sober reflections. Rabi reported that after the initial euphoria, a chill soon set in on those present. The test director, Kenneth Bainbridge, called the explosion a "foul and awesome display" and remarked to Oppenheimer, "Now we are all sons of bitches." Expressions of horror and remorse are especially common in the later writings of those who were present. Oppenheimer wrote that the experience called to his mind the legend of Prometheus, punished by Zeus for giving man fire, and said also that he thought fleetingly of Alfred Nobel's vain hope that dynamite would end wars. Most famously, Oppenheimer later recalled that the explosion had reminded him of a line from the Hindu holy text, the Bhagavad-Gita: "Now I am become Death, the destroyer of worlds." The terrifying destructive power of atomic weapons and the uses to which they might be put were to haunt many of the Manhattan Project scientists for the remainder of their lives.

The success of the Trinity test meant that both types of bombs -- the uranium design, untested but thought to be reliable, and the plutonium design, which had just been tested successfully -- were now available for use in the war against Japan. Little Boy, the uranium bomb, was dropped first at Hiroshima on August 6, while the plutonium weapon, Fat Man, followed three days later at Nagasaki on August 9. Within days, Japan offered to surrender.

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Sources and notes for this page.

The text for this page was adapted from, and portions were taken directly from the Office of History and Heritage Resources publication: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), 48-49. On the availability of additional plutonium bombs (but not uranium), see "The Manhattan Engineer District, 1945-1946." The "long-hairs" remark is quoted in Los Alamos Scientific Laboratory, Los Alamos: Beginning of an Era, 1943-1945 (Los Alamos: Public Relations Office, Los Alamos Scientific Laboratory, ca. 1967-1971), 53; the anecdotes re the final seconds of the countdown are from Los Alamos: Beginning of an Era, 50-51. Click here for information on the color photograph of Trinity. The photograph of SED Herb Lehr holding the Gadget's core is courtesy the Los Alamos National Laboratory (LANL) and is reprinted in Rachel Fermi and Esther Samra, Picturing the Bomb: Photographs from the Secret World of the Manhattan Project (New York: Harry N. Abrams, Inc., Publishers, 1995), 138. The following pictures are also courtesy LANL: the bunker at S-10,000, the plutonium core being unloaded from the car, the gadget being hoisted up the tower, the unidentified man sitting next to the gadget, and the photograph of Kenneth Bainbridge. The map of the Trinity Test Site is reproduced from Vincent C. Jones, Manhattan: The Army and the Atomic Bomb, United States Army in World War II (Washington: Center of Military History, United States Army, 1988), 479. The photograph of Robert Oppenheimerwith Leslie Grovesat the Trinity Site appears on the cover of the History Office publication: The Signature Facilities of the Manhattan Project (Washington: History Division, Department of Energy, 2001). The photograph of Fat Man is courtesy the U.S. Army Corps of Engineers (via the National Archives).