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Trinity: First Test of the Atomic Bomb

The world's first nuclear (atomic) explosion took place on 16 July 1945, 5:29:45 AM Mountain War Time at the Trinity Test Site, Alamogordo Bombing and Gunnery Range, New Mexico.

The exact location is: Latitude 33 40' 31'' N, Longitude 106 28' 29'' W.

Gadget atomic device being readied for Trinity Test, 15 July 1945
"Gadget" atomic device being readied for Trinity Test, 15 July 1945.

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Background to the Trinity Test

Atomic weapons were developed by the U.S. War Department Manhattan Project, a top secret effort started in 1942. Material for bombs was manufactured at Oak Ridge, TN (uranium) and Hanford, WA (plutonium). Use against Japan was planned, but first a test was required to ensure the bomb would actually work. From a list of eight sites in California, Texas, New Mexico and Colorado, Trinity Site was chosen for the test, an area already controlled by the U.S. government as part of the Alamogordo Bombing and Gunnery Range established in 1942. The secluded Jornada del Muerto Valley was perfect as it provided isolation for secrecy and safety, but was still reasonably close to the Los Alamos Laboratory, the engineering and scientific base of the Manhattan Project, about 230 miles to the north.

On 20 December 1944 military police set up security checkpoints around the area and started using jeeps and trucks to patrol the site perimiter. Utilities such as generators, wells, pumps and power lines were installed. A fire station was set up and supplies were arranged from nearly Socorro, NM.

The Jumbo Trinity Test Container

The bomb design to be used at Trinity Site actually involved two explosions. First a conventional explosion involving 5,300 pounds of TNT would compress the 15 pound plutonium core into a critical mass, then, a tiny fraction of a second later, a nuclear explosion would occur from a chain reaction in the plutonium. The scientists were sure the TNT would explode, but the plutonium explosion was just a theory. If the chain reaction failed to occur, the TNT would blow the very rare and dangerous plutonium all over the countryside.

Jumbo was a container 25 feet long, 10 feet in diameter weighing 214 tons, built by Eichleay Corporation of Pittsburgh to contain an aborted nuclear explosion. Project scientists planned to put the atomic bomb in this huge steel jug because it could contain the TNT explosion if the chain reaction failed to materialize. This would prevent the plutonium from being lost. If the nuclear explosion occurred as theorized, Jumbo would be vaporized. Jumbo was brought to Pope, NM, by rail and unloaded. A specially built trailer with 64 wheels was used to move Jumbo the 25 miles to Trinity Site (photo, right).

As confidence in the plutonium bomb design grew, along with concern about adding tons of radioactive steel vapor to the results of a successful test, it was decided not to use Jumbo. Instead, Jumbo was placed in a steel tower about 800 yards from ground zero. The test blast destroyed the tower, but Jumbo survived intact and can be seen today at the Trinity site.

Instrument Test at Trinity

To calibrate the instruments which would be measuring the atomic explosion and to practice a countdown, the Manhattan Project scientists ran a simulated blast on 7 May 1945. They stacked 100 tons of TNT onto a 20-foot wooden platform just southeast of ground zero. A small amount of radioactive material from Hanford was inserted into tubes running through the stack of TNT crates. The scientists hoped to get a feel for how the radiation might spread in the real test by analyzing this test. The explosion destroyed the platform, leaving a small crater with trace amounts of radiation in it.

Assembling Gadget, the Trinity Bomb

On 12 July 1945 the two hemispheres of plutonium metal prepared at Los Alamos were carried to the George McDonald ranch house, 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. Farrell later said:

I recall that I asked them if I was going to sign for it shouldn't I take it and handle it. So I took this heavy ball in my hand and I felt it growing warm, I got a certain sense of its hidden power. It wasn't a cold piece of metal, but it was really a piece of metal that seemed to be working inside. Then maybe for the first time I began to believe some of the fantastic tales the scientists had told about this nuclear power.

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 509th Composite Group 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, 13 July 1945, the explosive assembly left Los Alamos for Trinity Site. Later that 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, called simply "the Gadget", was assembled under the tower on 13 July (top photo, and left). 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 5:00 PM on 14 July it was complete.

The Trinity Test, the First Atomic Bomb

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 personnel such as Dr. Robert Oppenheimer, Director of Los Alamos, watched.

Many scientists and support personnel, including Gen. Leslie Groves, military head of the Manhattan Project, watched the explosion from base camp which was ten miles southwest of ground zero. Most visiting VIPs watched from Compania Hill, 20 miles northwest of ground zero.

The test was scheduled for 4:00 AM on 16 July, but rain and lightning early that morning caused a postponement. 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 AM the crucial weather report came through announcing calm to light winds with broken clouds for the following two hours.

At 5:10 AM the twenty minute countdown started and at 5:29:45 AM the device exploded, fully successfully. To most observers the brilliance of the light from the explosion--watched through welders' glasses--overshadowed the shock wave and sound that arrived later.

Dr. Oppenheimer quoted from Hindu scripture, the Bhagavad-gita, "Now I am become death, the destroyer of worlds."

Hans Bethe, one of the Manhattan Project scientists, wrote " looked like a giant magnesium flare which kept on for what seemed a whole minute but was actually one or two seconds. The white ball grew and after a few seconds became clouded with dust whipped up by the explosion from the ground and rose and left behind a black trail of dust particles."

Joe McKibben, another scientist, said, "We had a lot of flood lights on for taking movies of the control panel. When the bomb went off, the lights were drowned out by the big light coming in through the open door in the back."

Others were impressed by the heat they immediately felt. Military policeman Marvin Davis said, "The heat was like opening up an oven door, even at 10 miles." Dr. Phillip Morrison said, "Suddenly, not only was there a bright light but where we were, 10 miles away, there was the heat of the sun on our faces....Then, only minutes later, the real sun rose and again you felt the same heat to the face from the sunrise. So we saw two sunrises."

The blast was estimated as equivalent to 19,000 tons of TNT. The tower was vaporized leaving only stubs of the legs in concrete pilings. The explosion did not make much of a crater. Most eyewitnesses describe the area as more of a small depression instead of a crater.

After the Trinity Explosion

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 released a previously prepared press statement saying that a munitions storage area had accidentally exploded at the Alamogordo Bombing Range.

The heat of the Trinity blast melted the desert sand and turned it into a green glassy substance immediately named 'Trinitite' that can still be seen in the area. At one time Trinitite completely covered the depression made by the explosion. In the 1950's, the Army bulldozed most of the Trinitite from the site and partially filled the crater with dirt to control radiation levels. Most of the Trinitite was put in containers and taken away by the Atomic Energy Commission (later renamed the Nuclear Energy Commission).

Trinity Test Site Today

In 1965, a modest monument was erected at Ground Zero. Built of black lava rock, this monument serves as a permanent marker for the site and as a reminder of the momentous event that occurred there. On the monument is a plain metal plaque with this simple inscription: "Trinity Site Where the World's First Nuclear Device Was Exploded on July 16, 1945." The site is open to the public two days a year.

In 1975, a second plaque was added below the first by The National Park Service, designating Trinity Site a National Historic Landmark.

Find More Information on the Internet

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