Manhattan Project

Manhattan Project. The Manhattan Project refers to the Army Corps of Engineers' “Manhattan Engineer District,” the code name of the military project established in June 1942 for atomic‐bomb research and development.In the years leading up to World War II, many scientists pondered building nuclear weapons, particularly after Lise Meitner's and Otto Frisch's startling interpretation in 1938 of earlier uranium and neutron bombardment experiments (by Enrico Fermi and others) as nuclear fission.

Albert Einstein's August 1939 letter to President Franklin Delano Roosevelt (actually written by the Hungarian‐born emigré physicist Leo Szilard [1898–1964]) was one means by which the U.S. government became aware of the atomic potential. In late 1940, the British and American governments joined forces to establish an atomic‐bomb project in the industrially stronger and more protected country. Vannevar Bush, director of the government's new Office of Scientific Research and Development, drafted plans for the Manhattan Project, whose urgency was underscored by Japan's attack on Pearl Harbor on 7 December 1941. On 2 December 1942, less than three months after the appointment of Colonel (later Brigadier General) Leslie Groves as director of the Manhattan Project, Fermi demonstrated the first chain reaction at the University of Chicago. The Manhattan Project eventually grew into a three‐billion‐dollar conglomeration, which included the Chicago Metallurgical Laboratory; the Berkeley Radiation Laboratory; the Oak Ridge, Tennessee, and Hanford, Washington, materials‐production facilities; and the Los Alamos, New Mexico, laboratory, where the first atomic bombs were built.

Centralizing the many separate research efforts devoted to atomic‐bomb research was essential, both for efficiency and to maintain secrecy. J. Robert Oppenheimer, whom Groves appointed in 1942 to head the project, selected a site on a high mesa in New Mexico, the Los Alamos Ranch School. Here a large community of scientists, engineers, and military personnel worked behind a security fence in a town identified only by its post‐office box number (1663). Everyone at Los Alamos—even scientific luminaries, such as Fermi, Hans Bethe, Edward Teller, Richard Feynman, John von Neumann, George Kistiakowsky, Stanislav Ulam, and Niels Bohr—was assigned and reassigned as needed and required to work collaboratively in the mode later known as “big science.”

The technical program, geared initially toward “gun‐type” uranium and plutonium bombs (in which the fissionable material would be shot together), was abruptly realigned after the April 1944 discovery of a high level of spontaneous fission in reactor‐made plutonium. Attention then turned to the more rapid, and technically complex, assembly known as implosion. Despite enormous hurdles, an implosion bomb was successfully detonated at the “Trinity” test at Alamogordo, New Mexico, on 16 July 1945.

Told of the successful test while at the Potsdam Conference, President Harry S. Truman authorized dropping the uranium bomb that fell on Hiroshima on 6 August and the plutonium bomb dropped on Nagasaki on 9 August. These weapons, which killed more than 120,000 Japanese, are widely believed to have led directly to the Japanese surrender on 14 August. They marked the start of the nuclear age and touched off an arms race that persisted throughout the Cold War Era.
See also Hiroshima and Nagasaki, Atomic Bombing of; Nuclear Power; Nuclear Strategy; Physical Sciences; Science: From 1914 to 1945; Science: Since 1945.

Bibliography

Richard Rhodes , The Making of the Atomic Bomb, 1986.
Lillian Hoddeson,, Paul W. Henriksen,, Roger A. Meade,, and and Catherine Westfall , Critical Assembly: A Technical History of Los Alamos during the Oppenheimer Years, 1943–1945, 1993.

Lillian Hoddeson