Under the Manhattan Project three large facilities were constructed. At Oak Ridge, Tenn., huge gas diffusion and electromagnetic process plants were built to separate uranium 235 from its more common form, uranium 238. Hanford, Wash. became the home for nuclear reactors which produced a new element called plutonium. Both uranium 235 and plutonium are fissionable and can be used to produce an atomic explosion.
Los Alamos was established in northern New Mexico to design and build the bomb. At Los Alamos many of the greatest scientific minds of the day labored over the theory and actual construction of the device. The group was led by Dr. J. Robert Oppenheimer who is credited with being the driving force behind building a workable bomb by the end of the war.
Los Alamos scientists devised two designs for an atomic bomb--one using the uranium and another using the plutonium. The uranium bomb was a simple design and scientists were confident it would work without testing. The plutonium bomb worked by compressing the plutonium into a critical mass which sustains a chain reaction. The compression of the plutonium ball was to be accomplished by surrounding it with lens-shaped charges of conventional explosives. They were designed to all explode at the same instant. The force is directed inward, thus smashing the plutonium from all sides.
In an atomic explosion, a chain reaction picks up speed as atoms split, releasing neutrons plus great amounts of energy. The escaping neutrons strike and split more atoms, thus releasing still more neutrons and energy. In a nuclear explosion this all occurs in a millionth of a second with billions of atoms being split.
Project leaders decided a test of the plutonium bomb was essential before it could be used as a weapon of war. From a list of eight sites in California, Texas, New Mexico and Colorado, Trinity Site was chosen as the test site. The area already was controlled by the government because it was part of the Alamogordo Bombing and Gunnery Range which was established in 1942. The secluded Jornada del Muerto was perfect as it provided isolation for secrecy and safety, but was still close to Los Alamos.
In the fall of 1944 soldiers started arriving at Trinity Site to prepare for the test. Marvin Davis and his military police unit arrived from Los Alamos at the site on Dec. 30, 1944. The unit set up security checkpoints around the area and had plans to use horses to ride patrol. According to Davis the distances were too great and they resorted to jeeps and trucks for transportation.
On July 12 the two hemispheres of plutonium were carried to the George McDonald ranch house just two miles from ground zero. At the house, Brig. Gen. Thomas Farrell, deputy to Maj. Gen. Leslie Groves, was asked to sign a receipt for the plutonium.
At the McDonald ranch house the master bedroom had been turned into a clean room for the assembly of the bomb core. According to Robert Bacher, a member of the assembly team, they tried to use only tools and materials from a special kit. Several of these kits existed and some were already on their way to Tinian, the island in the Pacific which was the base for the bombers. The idea was to test the procedures and tools at Trinity as well as the bomb itself.
At one minute past midnight on Friday, July 13, the explosive assembly left Los Alamos for Trinity Site. Later in the morning, assembly of the plutonium core began. According to Raemer Schreiber, Robert Bacher was the advisor and Marshall Holloway and Philip Morrison had overall responsibility. Louis Slotin, Boyce McDaniel and Cyril Smith were responsible for the mechanical assembly in the ranch house. Later Holloway was responsible for the mechanical assembly at the tower.
In the afternoon of the 13th the core was taken to ground zero for insertion into the bomb mechanism. The bomb was assembled under the tower on July 13. The plutonium core was inserted into the device with some difficulty. On the first try it stuck. After letting the temperatures of the plutonium and casing equalize the core slid smoothly into place. Once the assembly was complete many of the men took a welcome relief and went swimming in the water tank east of the McDonald ranch house.
The next morning the entire bomb was raised to the top of the 100 foot steel tower and placed in a small shelter. A crew then attached all the detonators and by 5 p.m. it was complete.
Three observation points were established at 10,000 yards from ground zero. These were wooden shelters protected by concrete and earth. The south bunker served as the control center for the test. The automatic firing device was triggered from there as key men such as Dr. Robert Oppenheimer, head of Los Alamos, watched. None of the manned bunkers are left.
Many scientists and support personnel, including Gen. Leslie Groves, head of the Manhattan Project, watched the explosion from base camp which was ten miles southwest of ground zero. All the buildings at base camp were removed after the test. Most visiting VIPs watched from Compania Hill, 20 miles northwest of ground zero.
The test was scheduled for 4 a.m. July 16, but rain and lightning early that morning caused it to be postponed. The device could not be exploded under rainy conditions because rain and winds would increase the danger from radioactive fallout and interfere with observation of the test. At 4:45 a.m. the crucial weather report came through announcing calm to light winds with broken clouds for the following two hours.
At 5:10 the countdown started and at 5:29:45 the device exploded successfully. To most observers the brilliance of the light from the explosion--watched through dark glasses--overshadowed the shock wave and sound that arrived later.
Although no information on the test was released until after the atomic bomb was used as a weapon against Japan, people in New Mexico knew something had happened. The shock broke windows 120 miles away and was felt by many at least 160 miles away. Army officials simply stated that a munitions storage area had accidentally exploded at the Alamogordo Bombing Range.
The explosion did not make much of a crater. Most eyewitnesses describe the area as more of a small depression instead of a crater. The heat of the blast did melt the desert sand and turn it into a green glassy substance. It was called Trinitite and can still be seen in the area. At one time Trinitite completely covered the depression made by the explosion. Afterwards the depression was filled and much of the Trinitite was taken away by the Nuclear Energy Commission.
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| Los Alamos Main Gate |
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| Trinity Site Base Camp |
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| Base Camp |
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| Jumbo |
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| Jumbo |
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| Jumbo being raised |
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| Jumbo, post test |
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| 100 ton test |
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| Unloading the Pu239 Core |
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| Sgt. Herbert Lehr delivering the plutonium core |
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| Raising the Gadget |
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| Raising the Gadget |
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| The Gadget and Norris Bradbury |
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| Observation bunker |
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| Trinity Mushroom Fireball |
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| Trinity Mushroom Cloud |
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| Trinity Mushroom Cloud |
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| Trinity Mushroom Cloud |
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| Trinity Site monument |
On July 13, the explosive was put together underneath the skyscraper. With some effort, the plutonium core was placed into the gadget. It stuck on the first attempt. After letting the temperatures of the plutonium and casing equalize the core slid smoothly into place
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