The Gadget
When the Manhattan Project began finalizing atomic bomb designs in 1944, the scientists, led by J. Robert Oppenheimer, settled on two designs--one using uranium-235, the other using plutonium-239. The U-235 bomb, codenamed Little Boy, used a very simple detonation device: a gun essentially fired a "bullet" of U-235 into a block of more U-235, resulting in a nuclear explosion. Oppenheimer and the other scientists knew Little Boy would work; it didn't even need to be tested.
It was thought that the Pu-239 device--codenamed Thin Man--would be able to operate in the same fashion, but Manhattan Project scientists at Los Alamos, New Mexico, learned that the Thin Man design actually would detonate too early, and "fizzle": it would explode, but with the same force as a conventional bomb. The Project scrambled to figure something else out, and found that the Pu-239 bomb would work by detonating several conventional explosives around a plutonium core, essentially bombarding the core with shockwaves until it reached critical mass and exploded. Codenamed Fat Man for its size, in theory this design would work--in theory.
Oppenheimer and the Project's military commander, Leslie Groves, were not interested in theory: the bomb had to work. If it was dropped on the Axis and fizzled, not only would the United States look foolish, they would waste what little plutonium was available. The Fat Man design had to be tested with a ground explosion that would simulate an air-dropped bomb. This led to building a similar design to Fat Man, simply called the "Gadget." The Gadget lacked Fat Man's external casing and used a less efficient but simpler core design, since this was just a test device. The first half of 1945 was used figuring out the details of the Gadget, but by mid-July, it was ready. Oppenheimer codenamed the test Trinity.
The Gadget was hoisted up a 100-foot tower in the middle of the Jornada del Muerto ("Dead Man's Journey") desert in central New Mexico; as it was part of the Alamagordo Bombing Range, there was no need to evacuate anyone. It was armed on July 15, with detonation planned early on July 16, when it was hoped there would be fewer civilians to notice. There was still considerable concerns that the Gadget would either not work at all or fizzle. The scientists took bets, and Enrico Fermi amused himself by terrifying the guards, telling them that the atmosphere might ignite if they got the calculations wrong. Rain delayed the test, but at 5:29 AM, the Gadget was detonated.
It worked exactly as planned. The 24 kiloton blast vaporized the bomb and its tower, fused the desert sand into a green glasslike mineral named trinitite, and lit up the mountains around the detonation with light brighter than the sun. So bright was the explosion that it was noticed by an aircraft flying 30 miles away, and reportedly a blind girl traveling with her family 40 miles away near Socorro remarked "What was that?" Many of the scientists cheered, and Groves remarked "That's the end of the war." Oppenheimer was proud of his achievement at the time, but he later reflected that he was reminded of a line from the Hindu Bhagavad Gita: "I am become Death, the destroyer of worlds."
President Harry Truman was at the Potsdam Conference when he was informed of a successful detonation. The Fat Man type plutonium bomb would go on to be the main type of early aerial nuclear weapon; it would be used to frightening effect over Nagasaki, Japan on 9 August 1945--Little Boy had already annihilated Hiroshima three days before. As Groves predicted, it ended World War II, but left a world forever changed.
This very accurate replica of the Gadget is at the National Atomic Testing Museum in Las Vegas, Nevada, though this is the way the Gadget would have appeared before a casing was placed around it at the Trinity site. It's the centerpiece of a very informative exhibit about the Manhattan Project and the atomic bombings of Japan.
The Gadget
When the Manhattan Project began finalizing atomic bomb designs in 1944, the scientists, led by J. Robert Oppenheimer, settled on two designs--one using uranium-235, the other using plutonium-239. The U-235 bomb, codenamed Little Boy, used a very simple detonation device: a gun essentially fired a "bullet" of U-235 into a block of more U-235, resulting in a nuclear explosion. Oppenheimer and the other scientists knew Little Boy would work; it didn't even need to be tested.
It was thought that the Pu-239 device--codenamed Thin Man--would be able to operate in the same fashion, but Manhattan Project scientists at Los Alamos, New Mexico, learned that the Thin Man design actually would detonate too early, and "fizzle": it would explode, but with the same force as a conventional bomb. The Project scrambled to figure something else out, and found that the Pu-239 bomb would work by detonating several conventional explosives around a plutonium core, essentially bombarding the core with shockwaves until it reached critical mass and exploded. Codenamed Fat Man for its size, in theory this design would work--in theory.
Oppenheimer and the Project's military commander, Leslie Groves, were not interested in theory: the bomb had to work. If it was dropped on the Axis and fizzled, not only would the United States look foolish, they would waste what little plutonium was available. The Fat Man design had to be tested with a ground explosion that would simulate an air-dropped bomb. This led to building a similar design to Fat Man, simply called the "Gadget." The Gadget lacked Fat Man's external casing and used a less efficient but simpler core design, since this was just a test device. The first half of 1945 was used figuring out the details of the Gadget, but by mid-July, it was ready. Oppenheimer codenamed the test Trinity.
The Gadget was hoisted up a 100-foot tower in the middle of the Jornada del Muerto ("Dead Man's Journey") desert in central New Mexico; as it was part of the Alamagordo Bombing Range, there was no need to evacuate anyone. It was armed on July 15, with detonation planned early on July 16, when it was hoped there would be fewer civilians to notice. There was still considerable concerns that the Gadget would either not work at all or fizzle. The scientists took bets, and Enrico Fermi amused himself by terrifying the guards, telling them that the atmosphere might ignite if they got the calculations wrong. Rain delayed the test, but at 5:29 AM, the Gadget was detonated.
It worked exactly as planned. The 24 kiloton blast vaporized the bomb and its tower, fused the desert sand into a green glasslike mineral named trinitite, and lit up the mountains around the detonation with light brighter than the sun. So bright was the explosion that it was noticed by an aircraft flying 30 miles away, and reportedly a blind girl traveling with her family 40 miles away near Socorro remarked "What was that?" Many of the scientists cheered, and Groves remarked "That's the end of the war." Oppenheimer was proud of his achievement at the time, but he later reflected that he was reminded of a line from the Hindu Bhagavad Gita: "I am become Death, the destroyer of worlds."
President Harry Truman was at the Potsdam Conference when he was informed of a successful detonation. The Fat Man type plutonium bomb would go on to be the main type of early aerial nuclear weapon; it would be used to frightening effect over Nagasaki, Japan on 9 August 1945--Little Boy had already annihilated Hiroshima three days before. As Groves predicted, it ended World War II, but left a world forever changed.
This very accurate replica of the Gadget is at the National Atomic Testing Museum in Las Vegas, Nevada, though this is the way the Gadget would have appeared before a casing was placed around it at the Trinity site. It's the centerpiece of a very informative exhibit about the Manhattan Project and the atomic bombings of Japan.