The Manhattan ProjectIn the months following the bombing of Pearl Harbor the Manhattan Project–the
name given to the atomic bomb program because its original offices were in
Manhattan–grew very quickly. And although the Army had been involved since June of
1942, it was just beginning to realize that someone was going to have to be put in overall
charge. The man chosen was Leslie Richard Groves, a 46-year-old colonel in the Army
Corps of Engineers.
While he was a competent engineer, Groves was no scientist. He did not
understand the science behind building the atomic bomb, nor did he pretend to. He
needed someone who would be able to supervise the scientific side of the project. After
dismissing a number of candidates, Groves decided on who seemed like the most
improbable of candidate of all–38-year-old J. Robert Oppenheimer.
After he was officially given the job of laboratory director, Oppenheimer planned a
campaign of “absolutely unscrupulous recruiting of anyone we can lay our hands on.”1
He used his charismatic personality to recruit some of the greatest scientific talent in the
world to join the project. He then helped Groves find a location for his bomb-making
laboratory, tentatively called “Site Y.”
A number of southwestern sites were explored. On November 16, Oppenheimer,
Groves, and representatives from the Army Corps of Engineers were looking at a site at
Jemez Springs, New Mexico, a deep canyon about 40 mi. (64 km) northwest of Santa Fe.
Oppenheimer did not care too much for the site, nor did Groves. His main objection was
that there was no room for expansion. Oppenheimer then innocently remarked about
going back to Albuquerque via the Los Alamos Ranch School.
Groves liked Los Alamos at once, and began moving quickly. He called
Washington that very evening and began to buy the land. The Ranch School was having
financial trouble as a result of the war, and so it was more than happy to sell out. Within a
week, the land, the building, and other possessions of the school–including 1,600 books
and 60 horses–sold for $440,000.
Los Alamos, or “the Hill,” as it was commonly referred to, officially opened for
business on April 15, 1943.
All bombs, and especially those being developed at Los Alamos, release energy in
the form of light and heat.
A certain amount of energy, called the binding energy, is required to hold the
nucleus of an atom together. This energy is relatively small for light elements and steadily
increases for heavier elements as far as cobalt, iron, and nickel. After that, in still heavier
elements, it begins to decrease to the point that the binding energy of an extremely heavy
atom, such as uranium, is less than that of many, much lighter elements.
A small portion of the mass of each particle is lost when it enters a nucleus so that
a proton, for instance, actually weighs less inside the nucleus than outside. It must do this
to fit in. To do this, it converts some of its mass into energy. The combined mass loss of
all the particles of the nucleus equals the binding energy.
There are two processes by which particles can be made to lose weight. One,
called fission (the type of bombs dropped on Japan), happens when a heavy nucleus splits
apart into two lighter nuclei. These newly formed nuclei have a higher binding energy
than their heavier “parent” nucleus; therefore, they demand a further weight loss on the
part of their particles. The other process, called fusion, occurs when two light nuclei fuse
together to form a single heavier nucleus with a higher binding energy. In both cases the
particles must lose mass and release energy. Certain types of atoms with many protons
and neutrons in their nucleus are radioactive; they are unstable and may break apart
spontaneously. Other types, upon absorbing neutrons, break apart. In this process, the
entire nucleus falls apart into two pieces, releasing energy in the process, but only after the
nucleus temporarily increases its’ mass number by one. Two atoms, P-239 and U-235,
undergo this type of division and release energy at the same time. U-235 emits two or
three neutrons in the process, while P-239 emits many more. Either of these two atoms
may be used in an atomic bomb. After absorbing a neutron, an atom of these elements
emits several more neutrons, making a chain reaction possible. If the surrounding
structure is properly designed, the result is an explosion.
The amount of fissionable material needed to make an explosion is called the
critical mass, or the trigger quantity. Because a chain reaction would begin immediately,
the material cannot be place all together. It must be broken up and contained in pieces
that are smaller than the critical size. These pieces are then brought together in one
supercritical lump, and at the moment of detonation, neutrons are fired into it. Although
the energy released by each fissioning atom is tiny, an explosion results from the
cumulative energy of trillions of such atoms. However, the equivalent of this energy in
mass is miniscule. The bomb that leveled Nagasaki in 1945 released an amount of energy
equal to that of a third of the weight of a penny.
The basic principle of a self-containing chain reaction had first been demonstrated
in an experiment devised by the brilliant scientist Enrico Fermi on December 2, 1942.
On that day, at the squash courts of the University of Chicago’s Stagg Field was
the “atomic pile”–a nearly 500-ton pile of graphite bricks, stacked in 57 layers into which
cubes of uranium or uranium oxide were embedded which two shifts of workers had
labored for sixteen days to build. The twenty foot (6 m)-high structure had no blueprints,
or even plans, except for what existed in Fermi’s head. “Long control rods, plated with
the element cadmium, were set up so they could be inserted into holes in the graphite
bricks and withdrawn when required. The graphite would slow down the neutrons
emitted by the uranium and the cadmium would absorb them. As the control rods were
withdrawn, however, fewer of the neutrons from the uranium, resulting in greater
fission–more atoms split. At some point as the rods were withdrawn, fission would
produce neutrons faster than the cadmium could absorb them. The result would be a
self-sustaining chain reaction.”2
Stuffed into the balcony overlooking the squash court were about forty senior
scientists, while three young men were poised on a platform above the pile. They were
dubbed the “Suicide Squad,” because it was their job to douse the pile with a cadmium salt
solution if the experiment went out of control.
The only man on the floor was George Weil, a young physicist who would be the
one to slowly pull the last control rod out of the pile. There was a safety rod controlled by
a solenoid-activated catch designed to automatically fall into place and stop the chain
reaction if neutron activity surpassed a preset level. There was a project leader, armed
with an ax, ready to cut the rope so the rod would fall into place and hopefully stop the
reaction if things went wrong.
At exactly 10:37 am, the experiment began when Fermi instructed Weil to remove
the last cadmium rod. The neutron counters were then activated. Fermi had his six-inch
(15 cm) slide rule and was carefully calculating the rate of increase. It met his
expectation, so he then instructed Weil to move the rod out another six-inches. Once
again the counter was activated. Fermi began calculating again, and he seemed pleased.
The process continued for about an hour, when the safety rod was automatically
released with a loud crash. The release was unexpected, but Fermi knew the pile was still
At 2 o’clock that afternoon the safety rod was reset and the experiment continued.
At 3:25 Fermi told Weil to pull the control rod out another 12 inches (30 cm). “This is
going to do it,” he said. Moments later, Fermi announced to all that the pile had gone
At 3:53 P.M. the control rod was reinstated. This was the first controlled released
from the atomic nucleus. Many consider that moment in the freezing squash court the key
step in the development of the atomic bomb. After all that, the only thing left was the”engineering.”
There were really two types of bombs being developed at Los Alamos. The first
used U-235. It was to be detonated by using a modified artillery gun inside a bomb casing
to fire a lump of uranium onto a uranium target at 2,000 feet (610 m) per second. The
impact would produce a nuclear explosion. The only problem was that U-235 was so rare
that there would probably be enough of it to produce only one bomb over two years.
The second type was the theoretical bomb built from the artificial element
plutonium. No one there had actually seen the element, but they were reasonably sure that
there was enough of it to make multiple bombs. By July, however, the scientists
discovered that the tow subcritical masses of plutonium could not be brought together fast
enough to prevent premature explosion, thus ruling out the simple “gun assembly method
The solution, as suggested by one of Oppenheimer’s former students, physicist
Seth Neddermeyer, was “implosion.” He proposed that the plutonium should be
surrounded by a layer of high explosives that, when detonated, focused the blast so as to
compress the plutonium instantly into a supercritical mass. Being a much more
complicated procedure, most of the scientists who first heard it, including Oppenheimer,
did not think it could be made to work. The implosion theory became much more feasible
when the mathematician Jon von Neumann showed them his calculations that it could be
done, and would in fact require less of the precious fissionable material than the gun
By early 1944 a crisis had developed at Los Alamos–they were having difficulties
in getting adequate quantities of fissionable material.
General Groves had built a half-billion dollar secret factory in Oak Ridge,
Tennessee. It was only producing tiny amounts of pure U-235, and Oppenheimer was
informed he could count on enough of it for just one bomb by mid-1945.
Groves other secret factory, near Hanford, Washington, was working to produce
the other fissionable material, P-239. By 1945 it was estimated that Hanford was
producing enough of the plutonium for multiple bombs.
Everyone was absolutely convinced that the detonation of a uranium bomb by the
gun-method would work. However, by early 1944, it became increasingly obvious that
this would not work with the plutonium bomb. This meant that Neddermeyer’s implosion
method would have to be used. The problem with this, though, was that the plutonium
bomb’s technology was much newer and much more advanced, so it absolutely had to be
tested before it was used. And that meant that someplace in America had to be found to
test the most potentially awesome bomb that the world had ever seen.
The search for a suitable site to test the bomb began in May of 1944. The
requirements were very strict: it had to be relatively flat, both to minimize the effects of
the terrain on the bomb and to maximize the opportunities for a variety of experiments and
observations. The weather had to be basically good. The site had to be isolated from any
centers of population, yet close enough to Los Alamos to allow for the easy movement of
men and equipment.
That September, an area called the “Jornada del Muerto was finally settled on. It
is a stretch of desert lying between present-day Socorro and El Paso. It is bounded by the
San Andres and San Mateo mountains. The sandy soil supports only sparse vegetation,
and the summer temperatures often reach well over 100 degrees Fahrenheit (38 degrees
Celsius). Once the war started, the government leased several hundred miles to be used
for test bombing, and this test site became known as Trinity.
Construction on this site was full steam ahead by November. But, the construction
company did not even know what they were working on. The workers concluded that,
based on the fact they were building enormous concrete bunkers and reinforced steel
towers, the area had to do with powerful explosives.
Mid-July was not an ideal time for a test-bombing, as temperatures were often well
over 100 degrees Fahrenheit, and severe thunderstorms were common. The weather was
not the only problem the scientists encountered. The plutonium for the bomb did not
arrive at Los Alamos from Hanford until May 31, and prior to that no one had even seen
the artificial element. Up to that day, the bomb was all theory, existing only in the notes
and calculations of the scientists.
The plutonium core finally arrived as a syrupy nitrate, but still had to be purified
and transformed into metal. Two thirteen-and-a-half pound (6 kg) spheres, which had to
be exactly identical and completely smooth, were to be formed from the metal and used in
the core of the bomb.
On July 12, the plutonium core was taken to Trinity. It was in a rubber-studded
case in the backseat of an old army sedan, while up ahead a carload of armed guards
cleared the way, while assembly specialists brought up the rear.
On July13, the core was driven to the base of the 100 foot (30 m) tower at Trinity
for the final assembly. The heat caused the plutonium core to expand, though, and there
was a momentary panic when it would not click into its base. It finally cooled down and
was then clicked into place, then hoisted to the top of the tower with a power winch.
The test date was scheduled for 4:00 A.M. on July 16, 1945, but that time was
scratched because of approaching thunderstorms. At 2 A.M., Groves and Oppenheimer
drove from their observation post to a much nearer one and rescheduled the test for 5:30
AM.., weather permitting.
Shortly after 3 that morning the rain stopped, and at about 4 the clouds parted and the
winds began to die. At approximately 5 A.M., explosives expert George Kiatkowsky
checked the tower’s electrical connections, threw the final switches, and drove five miles
away to the South 10,000 control bunker. The countdown began at zero minus
The two-minute warning rocket failed, but the one-minute warning rocket and sire
went off as planned.
At 5:29 A.M., Sam Allison, the University of Chicago physicist who had
conducted the countdown, yelled “Zero!!”
Nothing happened. Then the sky suddenly ignited with an explosion of such a
magnitude the world had never seen before. The flash, as bright as twenty suns, was seen
in three states and threw up a multicolored mushroom cloud that surged 38,000 feet
(11,582 m) into the atmosphere in seven minutes. The heat at the center of the blast was
as great as that at the center of the sun. Where the fireball touched the ground there was a
crater a half-mile across, and it had fused the sand into a greenish-gray glass. Every living
thing within a radius of a mile–plants, snakes, ground squirrels, lizards, and even
The test that changed the world was a complete success, and said by Oppenheimer
to be “technically sweet.”
The Manhattan Project all but ended that day, after the bomb’s successful
detonation. Although there was still months of work to be done at Los Alamos, the real
action moved elsewhere.
As the Trinity test was being planned, so too was the bombing of Japan. After
Trinity the center of operations had moved to the island of Tinian, part of the Marshall
Islands chain in the Pacific Ocean. During the summer of 1945 the planners drew up a list
of potential targets for the bomb–Hiroshima, Kokura, Niigata, and Nagasaki. Hiroshima
was moved to the top of the list because it had a large military depot, an industrial area,
and was surrounded by hill which would help focus the blast. It was also the only place on
the list that did not contain Allied prisoner-of-war camps.
On July 26, President Truman issued what he called the Potsdam Declaration on
behalf of himself, the president of Nationalist China, and the Prime Minister of Great
Britain. There was no mention of the atomic bomb, but Truman included the threat of”utter destruction.” As was expected, Japan rejected President Truman’s declaration, so
the plan to drop an atomic bomb on Japan continued.
The plan called to first drop the reliable Little Boy uranium bomb. That would be
followed by the dropping of the plutonium based Fat Man bomb on a second, undecided
target. The plans also called for the production and use of as many plutonium bombs as
necessary to bring about the surrender of Japan. More and more bomb-making materials
were arriving at Tinian everyday, and B-29’s had already been modified to carry the new
weapon. Crews had been chosen and specially trained, though they were not actually told
what sold sort of weapon they were going to drop until the very last minute.
The plane that was going to carry the bomb had been known only as B-29 number
82. The day the bomb was loaded the mission pilot, Paul Tibbets, had his mother’s given
names “Enola Gay” painted on the fuselage.
The original plan called for the bomb to be fully armed at takeoff, but Captain
William “Deke” Parsons had seen too many B-29’s roll off the runway and catch fire. He
was afraid that if that happened to Enola Gay, it could trigger the bomb and blow up half
of the island. This worry made him decide to arm the bomb after takeoff.
The “Enola Gay” had been flying toward Japan for several hours before the bomb
was fully armed. The bomb bay doors swung open over Hiroshima on August 14, at 8:15
A.M. local time, and, lightened by nearly 10,000 pounds (4,540 kg) the plane lurched
upward. There was what seemed like a long delay and suddenly a bright light filled the
plane. First one shockwave, then another rattled it. Groves phoned Oppenheimer at Los
Alamos to tell him the bomb had gone off “with a very big bang.” Oppenheimer was not
as excited as Truman, but he was both pleased and happy.
The Japanese, both literally and figuratively, did not know what had hit them, but
before they could find out, they were hit again. On August 9, Fat Man, the plutonium
bomb, was dropped over the city of Nagasaki. More bombs were ready to go, but
Washington decided that they may not be necessary, as it looked like Japan was ready to
surrender. On August 15 the Japanese emperor went on the radio to announce that the
government had already notified the Allied powers of its’ surrender. It also happened to
be the first time that the Japanese people had ever heard their emperor’s voice.
The war was finally and completely over.
It was not until the bombing of Hiroshima that the entire world learned of the
existence of the atomic bomb. For most Americans it came as wonderful news. However,
to most people, the atomic bomb seemed like nothing more than a big bomb–they had no
idea of its’ destructive force, nor of the radiation.
Not even the scientists knew of the amount of radiation that would be released.
They knew that some dangerous radiation would be released by the blast, but the effects
of it were far from worse than anyone had imagined. Postwar censorship kept many of the
grisly details away from the American people for at least a year. And the worst effects of
the radiation–the leukemia, the cancer, the genetic damage–did not really show up for
several years. The atomic bomb was not just a bigger bomb; it totally changed the face of
“Atomic Bomb.” Encyclopedia Brittanica: Science and Tecnology Illustrated. 1984.
“Atomic Bomb.” McGraw-Hill Encyclopedia of Science and Technology. 1992.
Cohen, Daniel. The Manhattan Project. Brookfield, Connecticut: The Millbrook Press,
Kunetka, James W. City of Fire: Los Alamos and the Birth of the Atomic Age,
1943-1945. Englewood, New Jersey: Prentice-Hall, Inc., 1978