Trinity ( nuclear test ) Trinity was the code name of the first detonation of a nuclear device , conducted by the United States Army on July 16 , 1945 , as a result of the Manhattan Project , in the Jornada del Muerto desert about southeast of Socorro , New Mexico , at the new White Sands Proving Ground , which incorporated the Alamogordo Bombing and Gunnery Range . ( The site is now the White Sands Missile Range . ) Trinity used an implosion - design plutonium device , informally nicknamed " The Gadget " . Using the same conceptual design , the Fat Man device was detonated over Nagasaki , Japan , on August 9 , 1945 . The Trinity detonation produced the explosive power of about . Although nuclear chain reaction s had been hypothesized in 1933 and the first artificial self - sustaining nuclear chain reaction ( Chicago Pile - 1 or CP - 1 ) had taken place in December 1942 , the date of the Trinity test is usually considered to be the beginning of the Atomic Age . History . The creation of atomic weapons arose out of political and scientific developments of the late 1930s . The rise of fascist governments in Europe , new discoveries about the nature of atoms and the fear that Nazi Germany was working on developing atomic bombs converged in the plans of the United States , the United Kingdom , and Canada to develop powerful weapons using nuclear fission as their primary source of energy . Nuclear chain reaction s had been hypothesized in 1933 and the first artificial self - sustaining nuclear chain reaction ( Chicago Pile - 1 or CP - 1 ) had taken place in December 1942 , In 1939 a letter was sent by prominent physicists Leo Szilard and Albert Einstein to President Franklin D . Roosevelt warning of the possibility that Nazi Germany might be attempting to build an atomic bomb . In 1942 , Roosevelt authorized the Manhattan Project , as the American nuclear physics effort was called , to research and develop a nuclear device . Although Nazi Germany was defeated in May 1945 , the Manhattan Project was not disbanded , and culminated in the test explosion of a nuclear device at what is now called the Trinity Site on July 16 , 1945 , and the atomic bombings of Hiroshima and Nagasaki a few weeks later . The Manhattan Project . U . S . and British researchers were investigating the feasibility of nuclear weapons as early as 1939 . Practical development began in earnest in 1942 when these efforts were transferred to the authority of the U . S . Army and became the Manhattan Project . The weapons - development portion of this project was located at the Los Alamos Laboratory in northern New Mexico , though much other development and production work was carried out at the Clinton Engineer Works near Oak Ridge , Tennessee ( the separation of uranium - 235 ) ; the Hanford Engineer Works near Hanford , Washington ( the production and separation of plutonium - 239 ) ; in and near Chicago , Illinois ( at the University of Chicago and the Argonne National Laboratories ) ; and at the University of California , Berkeley . These research , development , and production efforts focused both on the development of the necessary fissile materials to power the nuclear chain reaction s in the atomic bombs and on the design , testing , and manufacture of the bombs themselves . From January 1944 until July 1945 , large - scale production plants were set in operation , and the fissile material thus produced was then used to determine the features of the weapons . Multi - pronged research was undertaken to pursue several possibilities for bomb design . Early decisions about weapon design had been based on minute quantities of uranium - 235 and plutonium that had been created in pilot plants and in physics - laboratory cyclotrons . From these experimental results , it was thought that the creation of a bomb was as simple as forming a critical mass of fissile material . The production of both uranium - 235 and plutonium - 239 were enormous undertakings given the technology of the 1940s and accounted for 80 % of the total costs of the project . Theoretically , enriching uranium was feasible through pre - existing techniques in physics ( e . g . , modifying particle accelerator technology ) , though it proved difficult to scale to industrial levels and was extremely costly . Plutonium , by contrast , could theoretically be produced most easily in nuclear reactors , but the technology and science involved was wholly new . The first experimental nuclear reactor had been developed and constructed by Enrico Fermi and his team of co - workers by the end of 1942 at the University of Chicago ( Chicago Pile - 1 ) , which proved that there were no obvious physical limitations to producing a slow - neutron nuclear chain reaction . Work began on constructing large plutonium - breeding reactors at Hanford , Washington , in October 1943 . The first reactor - bred plutonium was produced in the B - Reactor , the first full - scale plutonium - production reactor in the world . The first large batch of plutonium was refined at Hanford in the " 221 - T plant " , using the bismuth phosphate process , from December 26 , 1944 , to February 2 , 1945 . This was delivered to Oppenheimer ' s team at the Los Alamos laboratory on February 5 , 1945 . In the meantime , the X - 10 Graphite Reactor , a scaled - down version of the Hanford reactors , was built in Oak Ridge , Tennessee , and went into operation in November 1943 . Plutonium is a synthetic element not found in nature in appreciable quantities . It also has relatively complicated physics , chemistry , and metallurgy compared to most other elements . The only prior plutonium isolated for the project had been produced in cyclotrons in very minute amounts . In April 1944 , Emilio Segrè received the first sample of reactor - bred plutonium from the X - 10 reactor and discovered that it was not as pure as cyclotron - produced plutonium by a significant degree . Specifically , the longer the plutonium remained irradiated inside the reactor — which is necessary for high yields of the metal — the greater its content of the isotope plutonium - 240 . Pu - 240 undergoes spontaneous fission at an appreciable rate , and that releases excess neutrons . These extra neutrons implied a high probability that a gun - type bomb with plutonium would detonate too early , before a critical mass was formed , scattering the plutonium and producing a small " fizzle " of a nuclear explosion many times smaller than a full explosion . The practical result was that a simple gun - type atomic bomb ( the proposed Thin Man ) would not work as had been hoped . The impossibility of solving this problem of a gun - type bomb with plutonium was decided upon in a meeting in Los Alamos on June 17 , 1944 . This forced a search for a different , more practical design for a plutonium - fueled bomb , and an implosion - type atomic - bomb design ( " i . e . " , the Fat Man design ) was selected as the most practical one at that time . This required a great deal of research work and experimentation in engineering and hydrodynamics before a practical design could be worked out . In an implosion bomb , a small spherical core of plutonium would be surrounded by high explosives that burned with different speeds . By alternating the faster and slower burning explosives in a carefully calculated spherical configuration , they would produce a compressive wave upon their simultaneous detonation . This " lensing " effect focused the explosive force inward with enough force to compress the plutonium core to several times its original density . This would rapidly reduce the necessary size of the critical mass of the material , making it supercritical . It would also activate a small neutron source at the center of the core , which would assure that the chain reaction began in earnest . The advantage of the implosion method was that it was far more efficient in use of material — only 6 . 2 kg of plutonium would be needed for a full explosion , compared to the 64 kg of enriched uranium used in the " Little Boy " weapon . The engineering difficulties , though , were daunting . Though explosive lenses had been pursued during the war , the art was still very new , and the tolerances required in terms of timing and symmetry were unprecedented . Should the timing or symmetry be off , the bomb would not detonate fully , and instead just disperse the plutonium into the surrounding area . The entire Los Alamos laboratory was reorganized in 1944 to focus on designing a workable implosion bomb . Scientists were confident that an implosion device would work , but these new design difficulties were great . It was decided that a full - sized test would be required before any military use , even though it would sacrifice one of a very small number of bombs . In early 1945 , plans for a July 1945 test were finalized . The uranium weapon would not be tested ; its success could be more or less guaranteed by measurements ahead of time . The date of the Trinity test , Monday July 16 , was established in the belief that a successful test would enhance the position of President Truman , who was scheduled to meet with Allied leaders Winston Churchill and Joseph Stalin in Potsdam , Germany on Tuesday July 17 . The actual Fat Man atomic bomb , which used the same design as in the Trinity test , was exploded over Nagasaki on August 9 , 1945 , after the Trinity test had proven its operability in an atomic explosion . A third Fat Man bomb was expected to be ready by mid - August , if needed . " The gadget " was the code name given to the first bomb tested . It was so called because it was not a deployable weapon and because revealing words like " bomb " were not used during the project for fear of espionage . It was an implosion - type plutonium device , similar in design to the Fat Man bomb used three weeks later in the atomic bombing of Nagasaki , Japan . In the Fat Man design , a subcritical sphere of plutonium was placed in the center of a hollow sphere of high explosive . Numerous exploding - bridgewire detonator s located on the surface of the high explosive were fired simultaneously to produce a powerful inward pressure on the core , squeezing it and increasing its density , resulting in a supercritical condition and a nuclear explosion . The actual eventual Fat Man and the " gadget " devices were not strictly " Fat Man type " , as the design was modified into a production design , and both were strictly one - off prototypes . The gadget was tested at Trinity Site , New Mexico , near Alamogordo . For the test , the gadget was lifted to the top of a bomb tower . It was feared by some that the Trinity test might " ignite " the earth ' s atmosphere , eliminating all life on the planet , although calculations had determined this was unlikely . Less wild estimates thought that New Mexico would be incinerated . Calculations showed that the yield of the device would be between 0 ( if it did not work ) and . In the aftermath of the test , it appeared to have been a blast equivalent to . Test planning . In March 1944 , planning for the test was assigned to Kenneth Bainbridge , a professor of physics at Harvard University , working under explosives expert George Kistiakowsky . A site had to be located that would guarantee secrecy of the project ' s goals even as a nuclear weapon of unknown strength was detonated . Proper scientific equipment had to be assembled for retrieving data from the test itself , and safety guidelines had to be developed to protect personnel from the unknown results of a highly dangerous experiment . Official test photographer Berlyn Brixner set up dozens of cameras to capture the event on film . Test site . The heads of the project considered eight candidate sites , including San Nicolas Island ( California ) , Padre Island ( Texas ) , San Luis Valley , El Malpais National Monument , and other parts of New Mexico . A Mojave Desert Army base near Rice , California was considered the best location , but was opted against because General Leslie Groves , military head of the project , did not wish to have any dealings with the commander of the base , whom he disliked . The site finally chosen was at the northern end of the White Sands Proving Ground , in Socorro County between the towns of Carrizozo and San Antonio , in the Jornada del Muerto in the southwestern United States ( ) . In late 1944 , soldiers started arriving at Trinity Site to prepare for the test . Sgt . Marvin Davis and his military police unit arrived at the site from Los Alamos on December 30 , 1944 . This unit set up initial security checkpoints around the area , with plans to use horses for patrols . The distances around the site proved too great , so they resorted to using jeeps and trucks for transportation . Throughout 1945 , other personnel arrived at Trinity Site to help prepare for the bomb test . As the soldiers at Trinity Site settled in , they became familiar with Socorro County . They tried to use water out of the ranch wells , but found the water so alkaline they could not drink it . They were forced to use U . S . Navy saltwater soap and hauled drinking water in from the firehouse in Socorro . Gasoline and diesel fuel were purchased from the Standard Oil bulk plant in Socorro . Three bunker s were set up to observe the test . Oppenheimer and Brig . Gen . Thomas Farrell watched from the South bunker from the detonation , while Gen . Leslie Groves watched from the base camp away . Name . The exact origin of the name " Trinity " for the test is unknown , but it is often attributed to laboratory leader J . Robert Oppenheimer as a reference to the poetry of John Donne . In 1962 , General Groves wrote to Oppenheimer about the origin of the name , asking if he had chosen it because it was a name common to rivers and peaks in the West and would not attract attention , and elicited this reply : Test predictions . The observers set up a betting pool on the results of the test , with predictions ranging from zero ( a complete dud ) to . Physicist I . I . Rabi won the pool with a prediction of . In addition Fermi personally offered to take wagers among the top physicists and military present on whether the atmosphere would ignite , and if so whether it would destroy just the state , or incinerate the entire planet . This last result had been previously calculated to be almost impossible , although for a while it had caused some of the scientists some anxiety . Rhodes speculates that Fermi may have been making a point about a " new force being loosed on the Earth " , and how little really was known about it . Bainbridge was furious with Fermi for scaring the guards who , unlike the physicists , did not have the advantage of their knowledge about the scientific possibilities . Test preparation . A pre - test calibration explosion of , spiked with of fission products from the Hanford B Reactor , was detonated on a wooden platform to the south - east of Trinity ground zero ( ) on May 7 . The fireball of the conventional explosion was visible away . The smaller explosion proved an invaluable experiment that helped scientists prepare instruments in time to study the atomic bomb explosion two months later . For the actual test , the plutonium - core nuclear device , referred to as " the gadget , " was hoisted to the top of a steel tower for detonation — the height would give a better indication of how the weapon would behave when dropped from an airplane , as detonation in the air would maximize the amount of energy applied directly to the target ( as it expanded in a spherical shape ) and would generate less nuclear fallout . General Groves had ordered the construction of a steel canister code - named " Jumbo " to recover valuable plutonium if the of conventional explosives failed to compress it into a chain reaction . The container was constructed at great expense in Pittsburgh , Pennsylvania , and brought to the test site by rail , but by the time it arrived , the confidence of the scientists was high enough that they decided not to use it . Instead , it was hoisted up in a steel tower from the gadget as a rough measure of how powerful the explosion would be . In the end Jumbo survived , although its tower did not . The detonation was initially planned for 4 : 00 am but was postponed because of rain and lightning from early that morning . It was feared that the danger from radiation and fallout would be greatly increased by rain , and lightning had the scientists concerned about accidental detonation . Explosion . At 04 : 45 , a crucial weather report came in favorably , and , at 05 : 10 , the twenty - minute countdown began . Most top - level scientists and military officers were observing from a base camp southwest of the test tower . Many other observers were around away , and some others were scattered at different distances , some in more informal situations ( physicist Richard Feynman claimed to be the only person to see the explosion without the dark glasses provided , relying on a truck windshield to screen out harmful ultraviolet wavelengths ) . The final countdown was read by physicist Samuel K . Allison . At 05 : 29 : 21 ( plus or minus 2 seconds ) local time ( Mountain War Time ) , the device exploded with an energy equivalent to around . It left a crater of radioactive glass in the desert deep and wide . At the time of detonation , the surrounding mountains were illuminated " brighter than daytime " for one to two seconds , and the heat was reported as " being as hot as an oven " at the base camp . The observed colors of the illumination ranged from purple to green and eventually to white . The roar of the shock wave took 40 seconds to reach the observers . The shock wave was felt over away , and the mushroom cloud reached in height . After the initial euphoria of witnessing the explosion had passed , test director Kenneth Bainbridge commented to Los Alamos director J . Robert Oppenheimer , " Now we are all sons of bitches . " Oppenheimer later stated that , while watching the test , he was reminded of a line from the Bhagavad Gita , a Hindu scripture : " Now I am become Death , the destroyer of worlds . " Physicist Isidor Rabi noticed Oppenheimer ' s disconcerting triumphalism : " I ' ll never forget his walk ; I ' ll never forget the way he stepped out of the car . . . his walk was like " High Noon " . . . this kind of strut . He had done it . " In the official report on the test , General Farrell wrote , " The lighting effects beggared description . The whole country was lighted by a searing light with the intensity many times that of the midday sun . It was golden , purple , violet , gray , and blue . It lighted every peak , crevasse and ridge of the nearby mountain range with a clarity and beauty that cannot be described but must be seen to be imagined . . . " News reports quoted a forest ranger west of the site as saying he saw " a flash of fire followed by an explosion and black smoke . " A New Mexican north said , " The explosion lighted up the sky like the sun . " Other reports remarked that windows were rattled and the sound of the explosion could be heard up to away . John R . Lugo was flying a U . S . Navy transport at , east of Albuquerque , en route to the west coast . " My first impression was , like , the sun was coming up in the south . What a ball of fire ! It was so bright it lit up the cockpit of the plane . " Lugo radioed Albuquerque . He got no explanation for the blast but was told , " Don ' t fly south . " In the crater , the desert sand , which is largely made of silica , melted and became a mildly radioactive light green glass , which was named trinitite . The crater was filled in soon after the test . The Alamogordo Air Base issued a 50 - word press release in response to what it described as " several inquiries " that had been received concerning an explosion . The release explained that " a remotely located ammunitions magazine containing a considerable amount of high explosives and pyrotechnics exploded , " but that " there was no loss of life or limb to anyone . " A newspaper article published the same day stated that " the blast was seen and felt throughout an area extending from El Paso to Silver City , Gallup , Socorro , and Albuquerque . " An Associated Press article quoted a blind woman away who asked " What ' s that brilliant light ? " Such articles appeared in New Mexico , but East coast newspapers ignored them . The air base press release was written by William L . Laurence of " The New York Times " , who was aware of the Manhattan Project . He had prepared four releases for a variety of outcomes , ranging from an account of a successful test ( the one which was used ) to more catastrophic scenarios involving serious damage to surrounding communities , evacuation of nearby residents , and a placeholder for the names of those killed in the explosion . As Laurence was a witness to the test he knew that the last release , if used , would be his obituary . Around 260 personnel were present , none closer than . At the next test series , Operation Crossroads in 1946 , over 40 , 000 people were present . The official technical report ( LA - 6300 - H ) on the history of the Trinity test was released in May 1976 . Test results . The results of the test were conveyed to President Harry S . Truman , who was eagerly awaiting them at the Potsdam Conference ; the coded message ( " Operated this morning . Diagnosis not complete but results seem satisfactory and already exceed expectations . . . Dr . Groves pleased . " ) arrived at 7 : 30 p . m . on July 16 and was at once taken to the president and Secretary of State James F . Byrnes at the " Little White House " in the Berlin suburb of Babelsberg by Secretary of War Henry L . Stimson . Information about the Trinity test was made public shortly after the bombing of Hiroshima . The Smyth Report , released on August 12 , 1945 , gave some information on the blast , and the hardbound edition released by Princeton University Press a few weeks later contained the famous pictures of a " bulbous " Trinity fireball . Oppenheimer and Groves posed for reporters near the remains of the mangled test tower shortly after the war . In the years after the test , the pictures have become a potent symbol of the beginning of the so - called Atomic Age , and the test has often been featured in popular culture . First deployment . Following the success of the Trinity test , two bombs were prepared for use against Japan during World War II . The first , dropped on Hiroshima , Japan , on August 6 , was code - named " Little Boy " , and used the " gun " design and uranium - 235 as its fission source . It was an untested design but was considered very likely to work and was considerably simpler than the implosion model . It could not be tested , because there was only enough uranium - 235 for one bomb . The second bomb , dropped on Nagasaki , Japan , on August 9 , was code - named " Fat Man " and was a plutonium bomb of the type tested at Trinity . The atomic bombings of Hiroshima and Nagasaki killed at least 148 , 000 people and many more over time . By 1950 , the death toll was over 340 , 000 . They were followed days later by the surrender of Japan . Debate over the justification of the use of nuclear weapons against Japan persists to this day , both in scholarly and popular circles . Site today . In 1952 , the site of the explosion was bulldozed , and the remaining trinitite was disposed of . On December 21 , 1965 , the area Trinity Site was declared a National Historic Landmark district and , on October 15 , 1966 , was listed on the National Register of Historic Places . The landmark includes the base camp , where the scientists and support group lived ; ground zero , where the bomb was placed for the explosion ; and the Schmidt / McDonald ranch house , where the plutonium core to the bomb was assembled . Visitors to a Trinity Site open house are allowed to see the ground zero and ranch house areas . In addition , one of the old instrumentation bunkers is visible beside the road just west of ground zero . In September 1953 , about 650 people attended the first Trinity Site open house . In 1967 , the inner oblong fence was added . In 1972 , the corridor barbed wire fence that connects the outer fence to the inner one was completed . Jumbo was moved to the parking lot in 1979 ; it is missing its ends from an attempt to destroy it in 1946 using eight bombs . More than sixty years after the test , residual radiation at the site measured about ten times higher than normal . The amount of radioactive exposure received during a one - hour visit to the site is about half of the total radiation exposure which a U . S . adult receives on an average day from natural and medical sources . The Trinity monument , a rough - sided , lava - rock obelisk around high , marks the explosion ' s hypocenter , and Jumbo is still kept nearby . On July 16 , 1995 , a special tour of the site was conducted to mark the 50th anniversary of the Trinity test , and about 5 , 000 visitors arrived to commemorate the occasion , the largest crowd for any open house . Since that large crowd , the open houses usually average two to three thousand visitors . The site is still a popular destination for those interested in atomic tourism , though it is only open to the public once a year during the Trinity Site Open House on the first Saturday in April .