Processes
Uranium Mining, Milling, and Refining
TESTING THE BOMB
(1945)
Processes > Bomb Testing and Weapon Effects
The Manhattan Project scientists detonated the first atomic bomb at the Alamogordo Bombing Range in the New Mexico desert on July 16, 1945. This test, named "Trinity," used an implosion design with a plutonium core, much like the "Fat Man" bomb dropped on Nagasaki. Trinity was not only a demonstration that the complicated implosion device actually worked, it was also an important opportunity to learn about the properties of the atomic bomb before one could be prepared for actual wartime use. Initially, Manhattan Project officials and laboratory scientists had no intention of testing the bomb. The relatively simple gun method would be used for both uranium-235 and plutonium. With fissionable material in scarce supply and scientists possessing sufficient certitude that the gun device would provide a useable combat weapon, officials and scientists envisioned foregoing proof testing. The increasing likelihood that the implosion method would be required for a plutonium bomb, however, made them reconsider. Implosion was technically much more difficult to achieve, and prospects for a workable and useable implosion bomb without proof testing were uncertain at best. In late December 1943, John von Neumann, the Hungarian émigré mathematician and physicist who served as a part-time consultant to Los Alamos, suggested that implosion "fizzles," using "too small" quantities of "active material," that is, actual plutonium, would provide for testing "under much more realistic conditions than anything else—except the full-size gadget." The nuclear explosion would be "negligible compared to the imploding HE," and von Neumann suggested that "if this could be confined within a box of reasonable dimensions and thickness, which would not break, then the active material would be recovered by washing the inner surface of the box." He thought that a box with a ten-foot diameter made of eleven-inch armor plate would "do the trick." The idea of testing drew immediate—if qualified—support. In January 1944, General Leslie Groves reluctantly agreed to test the device as long as the plutonium could be recovered. The test would be a scaled-down explosion, along the lines of von Neumann's proposal, using a containment vessel. Los Alamos officials soon reconsidered this approach. Contending that performance would be easier to predict for a full-scale explosion, laboratory director J. Robert Oppenheimer in February recommended carrying out a full test in a remote location inside a containment vessel. Groves remained unenthusiastic. A successful test would consume significant amounts of precious plutonium. A failed or partially successful test might scatter plutonium across the countryside and, as he later put it, create "a health hazard that would make it necessary to guard the area against trespassers for many years." Without agreeing unequivocally to the test, Groves in March allowed the laboratory staff under the leadership of the Harvard physicist Kenneth T. Bainbridge to study the possibilities and move forward in procuring a suitable containment vessel, soon to be code-named "Jumbo." The determination in July 1944 that the plutonium gun would not work left implosion as the only short-term alternative for utilizing plutonium in a weapon and significantly increased the likelihood of a full-scale test. Site selection for the test began in spring 1944. Remote siting was a priority, with Los Alamos itself soon ruled out. Security dictated that any test blast must not be too closely linked with the laboratory, and insufficient space existed on the mesa to accommodate a possible explosion in the kiloton range. Bainbridge scoured maps of the western United States searching for the optimum site. Appropriate distance from Los Alamos was important, far enough away to avoid ready linkage with the laboratory but close enough to allow for ease of travel back and forth. Proper terrain and climate were critical. The site needed to be flat with infrequent haze and light winds so that the blast would not be hindered and prevent accurate measurements. Desert areas were preferable so that storms and rainfall could be avoided. Security and safety both demanded an isolated and sparsely settled region. "The area had to be remote," Bainbridge later observed, "so that people could be evacuated in the event of a low-order detonation, which would distribute poisonous plutonium, or a high-level explosion, which would be accompanied by dangerous radioactive fallout." Bainbridge and his site selection committee, which included Oppenheimer, initially considered eight different locations. Four sites were in New Mexico, two—the Tularosa and Jornada del Muerto valleys—in the arid southern part of the state, and two—the lava region south of Grants and the area southwest of Cuba and north of Thoreau—over the mountains to the west of the laboratory. Two sites were in California: on San Nicolas Island about seventy-five miles off the southern coast and at an Army tank training ground in the Mojave Desert near Rice. The remaining two sites were in the San Luis Valley near the Great Sand Dunes National Monument in southern Colorado and on a barrier island ten miles off the Texas Gulf Coast. After several exploratory expeditions, on one of which to the western New Mexico sites Oppenheimer participated in, Bainbridge and his committee narrowed the choices to either the California desert or the southern New Mexico valleys. Groves rejected the California location, reportedly because General George S. Patton was using the site and Groves refused to deal with him, and, in early September 1944, the Bainbridge committee settled on the Jornada del Muerto in the northwest corner of the Alamogordo Bombing Range about 100 miles south of Albuquerque. Plans for blast containment and possible recovery of plutonium in event of a failed or partially successful test proceeded apace. Los Alamos scientists settled on Jumbo's design in early August 1944. A hollow cylinder with dome ends and 15-inch thick steel walls, Jumbo measured 25 feet long and 12 feet in diameter and weighed 214 tons. In the end, no blast containment was used for the Trinity test. Planners, pressed by time and resource considerations to decide on test procedures, abandoned all recovery methods in March 1945 when Oppenheimer established Project TR (for Trinity) to oversee the test. Several factors influenced the decision to go with an unimpeded blast. The rate of plutonium production at Hanford had been higher than expected, and Oppenheimer concluded that sufficient plutonium would be available for a second test should the first one fail. There was also some fear that Jumbo might create safety problems of its own. A blast yielding over 500 tons, scientists calculated, would vaporize Jumbo, but an explosion in the region of 100 to 300 tons would, as Groves later put it, hurl "jagged pieces of steel… for great distances." An additional consideration was that use of blast containment would alter the blast characteristics of even a fully successful test and prevent the collection of accurate and easily analyzed blast data. Finally, scientists were becoming increasingly convinced that an implosion device would actually work. There would be, they now thought, no recoverable amounts of plutonium following a test.
Construction of a base camp at the Trinity site with barracks, officers' quarters, a mess hall, and other support facilities began in fall 1944.
Construction accelerated in early 1945 with the building of warehouses, repair shops, bomb-proof structures, an explosives magazine,
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a stockroom to house equipment shipped from Los Alamos, an unloading platform on the railroad siding at Pope 25 miles west of the site,
a commissary, and more barracks. Throughout May and June 1945 an entire laboratory grew in the desert, charged with designing a wide
variety of instruments to measure various bomb effects and capture images of the explosion in progress. One team of scientists needed
to study the design of the implosion mechanism itself, including the timing mechanisms of the
conventional 
The text for this page is original to the Department of Energy's Office of History and Heritage Resources. Portions were adapted or taken directly from OHHR's draft manuscript: Terrence R. Fehner and F. G. Gosling, Creating the Nuclear Environment, 1942-1954, chapter 4, and 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), 478-480. Also used were Richard G. Hewlett and Oscar E. Anderson, Jr., The New World, 1939-1946: Volume I, A History of the United States Atomic Energy Commission (Washington: U.S. Atomic Energy Commission, 1972); Lillian Hoddeson, et. al., Critical Assembly: A Technical History of Los Alamos during the Oppenheimer Years, 1943-1945 (Cambridge: Cambridge University Press, 1993); Kenneth T. Bainbridge, "Prelude to Trinity," Bulletin of Atomic Scientists (April 1975); and Bainbridge, "Trinity," LA-6300-H (Los Alamos: LASL, May 1976 [written in 1946, classified version internally published as LA-1012]). Von Neumann quote is found in Hoddeson, et. al., Critical Assembly, 157. Groves quotes are from Leslie M. Groves, Now It Can Be Told: The Story of the Manhattan Project (New York: Harper, 1962), 288-89. Bainbridge quote is from Bainbridge, "Prelude to Trinity," 44. The photographs of the Gadget arriving at the test site and being hoisted up the tower are courtesy of LANL.