Manhattan Project

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This article is about the atomic bomb project. For other uses, see Manhattan Project (disambiguation).

Manhattan District
The Manhattan Project created the first nuclear bombs. The Trinity test is shown.
Active	1942–1946
Country	United States  United Kingdom  Canada
Branch	United States Army Corps of Engineers
Garrison/HQ	Oak Ridge, Tennessee
Anniversaries	13 August 1942
Engagements	Allied Invasion of Italy Allied Invasion of France Allied Invasion of Germany Atomic bombings of Hiroshima and Nagasaki Allied Occupation of Japan
Disbanded	15 August 1947
Commanders
Notable commanders	Kenneth Nichols
Insignia
Shoulder patch that was adopted in 1945 for the Manhattan District
Manhattan Project emblem (unofficial)

The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army Corps of Engineers. The Army component of the project was designated theManhattan District; "Manhattan" gradually superseded the official codename, "Development of Substitute Materials", for the entire project. Along the way, the Manhattan Project absorbed its earlier British counterpart, Tube Alloys.

The Manhattan Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly US$2 billion (roughly equivalent to $25.8 billion as of 2012^[1]). Over 90% of the cost was for building factories and producing the fissionable materials, with less than 10% for development and production of the weapons. Research and production took place at more than 30 sites, some secret, across the United States, the United Kingdom and Canada. Two types of atomic bomb were developed during the war. A relatively simple gun-type fission weapon was made using uranium-235, an isotope that makes up only 0.7 percent of natural uranium. Since it is chemically identical to the main isotope,uranium-238, and has almost the same mass, it proved difficult to separate. Three methods were employed for uranium enrichment: electromagnetic,gaseous and thermal. Most of this work was performed at Oak Ridge, Tennessee.

In parallel with the work on uranium was an effort to produce plutonium. Reactors were constructed at Hanford, Washington, in which uranium was irradiated and transmuted into plutonium. The plutonium was then chemically separated from the uranium. The gun-type design proved impractical to use with plutonium so a more complex implosion-type weapon was developed in a concerted design and construction effort at the project's weapons research and design laboratory in Los Alamos, New Mexico. The first nuclear device ever detonated was an implosion-type bomb at the Trinity test, conducted at New Mexico's Alamogordo Bombing and Gunnery Range on 16 July 1945. Little Boy, a gun-type weapon, and the implosion-type Fat Man were used in the atomic bombings of Hiroshima and Nagasaki, respectively.

The Manhattan Project operated under a blanket of tight security, but Sovietatomic spies still penetrated the program. It was also charged with gathering intelligence on the German nuclear energy project. Through Operation Alsos, Manhattan Project personnel served in Europe, sometimes behind enemy lines, where they gathered nuclear materials and rounded up German scientists. In the immediate postwar years the Manhattan Project conducted weapons testing atBikini Atoll as part of Operation Crossroads, developed new weapons, promoted the development of the network of national laboratories, supported medical research into radiology and laid the foundations for the nuclear navy. It maintained control over American atomic weapons research and production until the formation of the United States Atomic Energy Commission in January 1947.

Contents   [hide]  1 Origins 2 Feasibility 2.1 Proposals 2.2 Bomb design concepts 3 Organization 3.1 Manhattan District 3.2 Military Policy Committee 3.3 Collaboration with the United Kingdom 4 Project sites 4.1 Oak Ridge 4.2 Los Alamos 4.3 Argonne 4.4 Hanford 4.5 Canadian sites 4.6 Heavy water sites 5 Uranium 5.1 Ore 5.2 Isotope separation 5.2.1 Centrifuges 5.2.2 Electromagnetic separation 5.2.3 Gaseous diffusion 5.2.4 Thermal diffusion 5.3 Gun-type weapon design 6 Plutonium 6.1 X-10 Graphite Reactor 6.2 Hanford reactors 6.3 Separation process 6.4 Weapon design 6.5 Trinity 7 Personnel 8 Espionage 9 Foreign intelligence 10 Bombing of Hiroshima and Nagasaki 10.1 Preparations 10.2 Bombings 11 After the war 12 Cost 13 Legacy 14 Notes 15 References 16 External links

Origins

In August 1939, prominent physicists Leó Szilárd and Eugene Wigner drafted the Einstein–Szilárd letter, which warned of the potential development of "extremely powerful bombs of a new type". It urged the United States to take steps to acquire stockpiles of uranium ore and accelerate the research of Enrico Fermi and others into nuclear chain reactions. They had it signed by Albert Einstein and delivered to President Franklin D. Roosevelt. Roosevelt called on Lyman Briggs of the National Bureau of Standards to head the Advisory Committee on Uranium to investigate the issues raised by the letter. Briggs held a meeting on 21 October 1939, which was attended by Szilárd, Wigner and Edward Teller. The committee reported back to Roosevelt in November that uranium "would provide a possible source of bombs with a destructiveness vastly greater than anything now known."^[2]

Briggs proposed that the National Defense Research Committee (NDRC) spend $167,000 on research into uranium, particularly theuranium-235 isotope, and the recently discovered plutonium.^[3] On 28 June 1941, Roosevelt signed Executive Order 8807, which created the Office of Scientific Research and Development (OSRD),^[4] with Vannevar Bush as its director. The office was empowered to engage in large engineering projects in addition to research.^[3] The NDRC Committee on Uranium became the S-1 Uranium Committee of the OSRD; the word "uranium" was soon dropped for security reasons.^[5]

In Britain, Otto Frisch and Rudolf Peierls at the University of Birmingham had made a breakthrough investigating the critical mass of uranium-235 in June 1939.^[6] Their calculations indicated that it was within an order of magnitude of 10 kilograms (22 lb), which was small enough to be carried by a bomber of the day.^[7] Their March 1940 Frisch–Peierls memorandum initiated the British atomic bomb project and its Maud Committee,^[8] which unanimously recommended pursuing the development of an atomic bomb.^[7] One of its members, the Australian physicist Mark Oliphant, flew to the United States in late August 1941 and discovered that data provided by the Maud Committee had not reached key American physicists. Oliphant then set out to find out why the committee's findings were apparently being ignored. He met with the Uranium Committee, and visited Berkeley, California, where he spoke persuasively toErnest O. Lawrence. Lawrence was sufficiently impressed to commence his own research into uranium. He in turn spoke to James B. Conant, Arthur Compton and George Pegram. Oliphant's mission was therefore a success; key American physicists were now aware of atomic bomb's potential.^[9][10]

At a meeting between President Roosevelt, Vannevar Bush and Vice President Henry A. Wallace on 9 October 1941, the President approved the atomic program. To control it, he created a Top Policy Group consisting of himself—although he never attended a meeting—Wallace, Bush, Conant, Secretary of War Henry L. Stimson and the Chief of Staff of the Army, General George Marshall. Roosevelt chose the Army to run the project rather than the Navy, as the Army had the most experience with management of large-scale construction projects. He also agreed to coordinate the effort with that of the British, and on 11 October he sent a message to Prime Minister Winston Churchill, suggesting that they correspond on atomic matters.^[11]

Feasibility