Manhattan Project

MANHATTAN PROJECT

MANHATTAN PROJECT, the secret American effort during World War II to construct an atomic bomb. Following the discovery of nuclear fission in Nazi Germany in late 1938, physicists the world over recognized the possibility of utilizing the enormous energy released by the splitting of an atom. If enough neutrons could be emitted by any given "broken" atom, such that at least one neutron struck another atom, causing it to break apart, a self-perpetuating "chain reaction" would result. Such a process, if controlled at a suitable rate, could serve as a power source, or "reactor." If a chain reaction proceeded unchecked, it could result in an explosion of unprecedented magnitude.

Several European scientists who had fled Nazi persecution in Europe felt it was their duty to alert the U.S. government to this new danger. In August 1939, the Hungarian émigré physicist Leo Szilard convinced Albert Einstein to write President Franklin D. Roosevelt and urge increased government support for research on the element most likely to support a chain reaction, uranium. By early 1940, government funding had commenced on a variety of related subjects, and in 1941 a series of studies confirmed the potential that uranium research held to create a usable weapon before the end of the war. In January 1942—only weeks after the Japanese attack on Pearl Harbor—Roosevelt gave the go-ahead to proceed with a full-scale effort to develop the atomic bomb.

By this time it was obvious that large factories would eventually have to be built. Because the work was now being done in secrecy, and considerable construction was foreseen, the Manhattan Engineer District of the U.S. Army Corps of Engineers was created in August 1942 to oversee the entire atomic bomb program. (It was initially headquartered in New York in order to be close to the fission research then being conducted at Columbia University.) The following month, Colonel Leslie R. Groves was promoted to brigadier general and given command of what was coming to be known as the Manhattan Project. Groves quickly brought in major contractors such as Stone and Webster and the Dupont Chemical Company. Less than four years after the discovery of fission, the program to build an atomic bomb had grown from a primarily academic pursuit to what was becoming, by September 1942, a prototypical example of what Dwight D. Eisenhower would later dub the "military-industrial complex." At its height a mere three years later, the Manhattan Project employed more than 130,000 men and women, having already spent more than $2 billion.

The most pressing problem immediately facing Groves was the acquisition, in an extremely short amount of time, of a quantity of fissionable material sufficient first for experimentation and thereafter for the production of at least one bomb. The kind of uranium needed to generate a chain reaction, the isotope U-235, comprised only 0.7 percent of all naturally occurring uranium, and a variety of exotic and unproven techniques were proposed for "enriching" uranium, or increasing the amount of U-235 contained in a sample. Following a period of intense debate, the scientists in November 1942 made their best guess as to which of these methods showed the most promise, choosing gaseous diffusion and electromagnetic separation. Groves immediately ordered the construction of two massive, full-scale uranium-enrichment plants. In less than three years their site at Oak Ridge, Tennessee, grew from remote farmland to the fifth largest town in the state.

In early 1941, a second path to the atomic bomb was pioneered by the discovery of a new element: plutonium. This substance did not occur in nature but could be created by irradiating common uranium. In December 1942, Enrico Fermi demonstrated this by producing the world's first controlled nuclear chain reaction in a "pile," or reactor, constructed beneath the west stands of the University of Chicago's Stagg Field. Soon, three gigantic reactors were under construction on the banks of the Columbia River near Hanford, Washington, to mass produce plutonium.

The final task remaining was to devise the actual means by which these "special nuclear materials" could be transformed into practical weapons. In late 1942, Groves placed J. Robert Oppenheimer in charge of the

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new weapons laboratory to be built on an isolated mesa in the desert at Los Alamos, New Mexico. Oppenheimer soon managed to assemble a virtual "dream team" of scientists drawn from around the world. Relatively little difficulty was encountered in the design of a uranium weapon. One piece of U-235 could be fired at another in a gun barrel, such that together they would form a critical, or explosive, mass. For technical reasons this crude method was unsuitable for plutonium, however, and, ultimately, a new technique called implosion was conceived, wherein a small sphere of plutonium was rapidly compressed to critical mass by conventional high explosives.

There had never been much doubt that "Little Boy," the gun-type uranium weapon, would work, and on 14 July 1945 it was shipped from Los Alamos to begin its journey westward toward Japan. Because the implosion process was so novel, however, a test of the plutonium design was held near Alamagordo, New Mexico, on 16 July 1945. This test, named "Trinity" by Oppenheimer, exceeded the expectations of almost every scientist at Los Alamos by exploding with a force equivalent to more than 18,000 tons of TNT. Oppenheimer later reported that the blast reminded him of a line from the Bhagavad-Gita: "Now I am become Death, the destroyer of worlds." The reaction of the test director, Kenneth Bainbridge, was more succinct: "Now we are all sons of bitches." On the morning of 6 August 1945, an American B-29 bomber dropped the uranium bomb on the Japanese port city of Hiroshima; three days later the second, plutonium device "Fat Man," was dropped on Nagasaki. Japan offered to surrender the following day. Although estimates vary, it is likely that by the end of 1945, there were at least 200,000 deaths directly attributable to the two bombings. Most were civilians. The total number of deaths after five years, including radiation and other secondary effects, may have been well over 300,000. At the beginning of 1947, control of the growing U.S. nuclear arsenal was formally transferred to the civilian Atomic Energy Commission, and in August of that year, the Manhattan Engineer District was formally disbanded.

BIBLIOGRAPHY

Gosling, F. G. The Manhattan Project: Making the Atomic Bomb. Washington, D.C.: History Division, Department of Energy, 1999.

Hewlett, Richard G., and Oscar E. Anderson Jr. A History of the United States Atomic Energy Commission. Vol. 1: The New World, 1939–1946. University Park: Pennsylvania State University Press, 1962. Comprehensive official history.

Rhodes, Richard. The Making of the Atomic Bomb. New York: Simon and Schuster, 1986. Pulitzer Prize–winning account focusing on the activities at Los Alamos.

David Rezelman

Lawrence Badash

See also Nuclear Weapons ; World War II .