The Manhattan Project

Manhattan District
The Trinity test of the Manhattan Project was the first detonation of a nuclear weapon.
Active	1942–1946
Country	United States of America  United Kingdom  Canada
Branch	U.S. Army Corps of Engineers
Garrison/HQ	Oak Ridge, Tennessee, U.S.
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	James C. Marshall 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 undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U.S. Army Corps of Engineers. Nuclear physicist J. Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the actual bombs. The Army component of the project was designated the Manhattan District; "Manhattan" gradually superseded the official codename, Development of Substitute Materials, for the entire project. Along the way, the 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 (about $27 billion in 2016 dollars). Over 90% of the cost was for building factories and to produce fissile material, with less than 10% for development and production of the weapons. Research and production took place at more than 30 sites across the United States, the United Kingdom, and Canada.

Two types of atomic bombs were developed concurrently during the war: a relatively simple gun-type fission weapon and a more complex implosion-type nuclear weapon. The Thin Man gun-type design proved impractical to use with plutonium so a simpler gun-type called Little Boy was developed that used uranium-235, an isotope that makes up only 0.7 percent of natural uranium. Chemically identical to the most common isotope, uranium-238, and with almost the same mass, it proved difficult to separate the two. Three methods were employed for uranium enrichment: electromagnetic, gaseous and thermal. Most of this work was performed at the Clinton Engineer Works at Oak Ridge, Tennessee.