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At 5:29:45 am Mountain War Time on July 16, 1945, the world’s first atomic bomb exploded one hundred feet over a portion of the southern New Mexico desert known as the Jornada del Muerto – the Journey of the Dead Man. On seeing the fireball and mushroom cloud, J. Robert Oppenheimer recalled a passage from the Bhagavad-Gita: "I am become death the destroyer of worlds." Trinity Test Director, Harvard Physicist Kenneth Bainbridge, had a less ethereal reaction, saying, "Now we are all sons of bitches."


The Trinity test was the first ever test of a nuclear device

A New Method: Implosion

In the first months of operations at Los Alamos in the spring of 1943, Oppenheimer and others believed that the first atomic bomb would be a gun that would shoot one piece of uranium or plutonium at a second piece of identical material. When the two pieces came together, a nuclear explosion would take place. From April 1943 until mid-summer 1944, almost all work at Los Alamos centered on designing and building such a gun. Experiments directed by future Nobel Prize winner Emilio Segre, however, demonstrated that plutonium could not be used in a gun. Impurities in the metal, which could not be removed, would cause a fizzle. It seemed, for a short time, that plutonium could not be used to make an atomic bomb. Because of serious problems in producing uranium, the plutonium problem put the entire atomic bomb program at risk.

The technical solution to this problem lay in the use of high explosives. Seth Neddermeyer proposed using the supersonic shock waves produced by high explosives to crush, or implode, a ball of plutonium to a supercritical state. If a ball of plutonium could be imploded symmetrically to a supercritical state, a nuclear explosion would follow. Seeing the technical merit of this approach, Oppenheimer reorganized the Los Alamos Laboratory in the summer of 1944 to concentrate work in this area. However, since this possible solution was new and untried, a test of such a gadget would be necessary.

Where Will it be Tested

Once the decision to test the implosion gadget was made, a test site had to be selected. Eight locations were proposed and evaluated:

Trinity Base Camp

Trinity Test Site

  1. The Tularosa Valley in southern New Mexico
  2. The Jornada del Muerto, also in southern New Mexico
  3. The Army's desert training area near Rice, California
  4. San Nicholas Island, off the coast of Southern California
  5. The lava region south of Grants, New Mexico
  6. An area in New Mexico southwest of Cuba, and north of Thoreau
  7. Sand bars, about 10 miles from the main coast of southern Texas
  8. The San Luis Valley region near the Great Sand Dunes National Monument in southern Colorado

Bainbridge used five criteria in evaluating these sites. First, the area had to flat to minimize effects on the blast. Second, the weather needed to V Site,, with little dust, haze, or strong winds. Third, the area needed to be remote from populated areas. Fourth, the site had to be relatively close to Los Alamos to minimize transportation problems. Finally, the site had to be isolated to enhance security. Using these criteria, Bainbridge narrowed the choice to the Jornada del Muerto, and the Army's desert training area near Rice, California. The Jornada del Muerto close to Los Alamos and easier to acquire, was selected.

The Journey of the Dead Man

Beginning in October 1944, the Jornada del Muerto became the site of ever increasing activity as Trinity Site was prepared for the test. A base camp was built to house staff. A one-hundred foot shot tower was designed and constructed at ground zero. Concrete bunkers to house cameras and other diagnostic equipment popped up in a rough circle around ground zero. Many of these bunkers were given names pegged to their proximity to the shot tower, such as "North 10,000." In March 1945, a July date was set for the Trinity test. However the actual day, July 16th, was not selected until the end of June, when the last of the technical issues had been addressed. In addition, a commitment had been made to test the gadget "as soon after July 15th as possible," and before or during the upcoming Potsdam Conference.

Oppenheimer Groves at Ground Zero

The plutonium was driven to Trinity site on July 11th in the back of Plymouth sedan. The high-explosive sphere, approximately five feet in diameter, followed on July 13th, lashed to the bed of an Army truck. Norris Bradbury, who would succeed Oppenheimer as Director of Los Alamos, wrote the procedures for assembling the gadget. His timetable called for the gadget to be completely assembled and lifted to the top of the tower on Saturday, July 14th. Bradbury’s timetable for Sunday, July 15th, reflected both Bradbury’s sense of humor as well as the strain everyone felt on the eve of the test. Bradbury wrote, "Look for rabbit’s feet and four-leaved clovers. Should we have the Chaplain down there? Period for inspection available from 0900-1000." The timetable for July 16th had just one word – "Bang!"

"A foul and awesome display"

Delayed for a time by a worrisome thunderstorm, the test erupted over the desert floor with what Bainbridge termed "a foul and awesome display." For observers standing from six to ten miles away, the site was fearsome. Enrico Fermi, not wanting to wait hours and days for the complex diagnostic data to be evaluated, decided to conduct an ad-hoc experiment to calculate the yield of the gadget. Wrote Fermi, "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, at the time, there was no wind, I could observe very distinctly and actually measure the displacement of the pieces of paper that were in the process of falling while the blast wave was passing. The shift was about two and a half meters, which at the time, I estimated to correspond to the blast that would be produced by ten thousand tons of TNT." While Fermi’s estimate was on the low side, his calculation did prove the enormous energy release was demonstrably more than could be achieved by conventional bombs.

Related Reading

The Test Director's Report
(PDF 4.2 MB)

Groves to Oppenheimer on the upcoming Trinity test
April 27, 1945
(PDF 109 KB)

Scheduling the Trinity Test
June 14, 1945
(PDF 217 KB)

Memorandum on the Immediate After Effects of the Gadget, Hans Bethe and Robert Christy
(PDF 149 KB)

Enrico Fermi's Observations at Trinity
July 16, 1945
(PDF 94 KB)

Victor Weisskopf's Eyewitness Account of Trinity
July 24, 1945
(PDF 124 KB)

Visual Observations of Elizabeth and Alvin Graves
July 24, 1945
(PDF 57 KB)

Navy Captain Larkin's Description of the Trinity Test
July 27, 1945
(PDF 130 KB)

Ralph Carlisle Smith's Comments on Trinity
September 5, 1945
(PDF 242 KB)

50th Anniversary Article:

Trinity: Completion of the Wartime Mission

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