Manhattan Project Timeline

(1939 - 1946)

The Manhattan Project was the top-secret U.S. government research and development program, led by General Leslie Groves with scientific direction from J. Robert Oppenheimer, that produced the world's first nuclear weapons. Spanning from 1939 to 1946, it involved over 130,000 workers at sites including Los Alamos, Oak Ridge, and Hanford, culminating in the atomic bombings of Hiroshima and Nagasaki in August 1945. More Less

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Scientific Origins

Discovery of nuclear fission

Dec 1938

German chemists Otto Hahn and Fritz Strassmann, working with physicist Lise Meitner's theoretical interpretation, discovered that uranium atoms could be split when bombarded with neutrons, releasing enormous energy. This discovery of nuclear fission laid the scientific foundation for the development of atomic weapons and nuclear power.

Image source: Nuclear fission

Einstein–Szilárd letter warns Roosevelt

Aug 2, 1939

Physicists Leo Szilárd and Albert Einstein co-signed a letter to President Franklin D. Roosevelt warning that Nazi Germany might develop atomic weapons and urging the United States to accelerate its own uranium research. The letter helped prompt the creation of the Advisory Committee on Uranium.

Image source: Einstein–Szilard letter

MAUD Committee report on bomb feasibility

Jul 1941

The British MAUD Committee concluded that a fission bomb was scientifically feasible and could likely be built within two years. Its report, shared with American officials, galvanized U.S. efforts and provided key technical direction for the eventual Manhattan Project.

Image source: MAUD Committee

Organization and Research

Creation of the Advisory Committee on Uranium

Oct 21, 1939

President Roosevelt established the Advisory Committee on Uranium, chaired by Lyman Briggs, to investigate the military potential of atomic energy. The committee's initial modest funding marked the first official American step toward developing nuclear weapons.

Image source: S-1 Executive Committee

Formation of the S-1 Executive Committee

Dec 6, 1941

Just before Pearl Harbor, the U.S. reorganized its atomic research under the S-1 Executive Committee of the Office of Scientific Research and Development, chaired by James B. Conant. This body coordinated early research into isotope separation and reactor design.

Manhattan Engineer District established

Aug 13, 1942

The U.S. Army Corps of Engineers created the Manhattan Engineer District to manage the atomic bomb program. Colonel (later General) Leslie Groves was appointed director in September 1942, bringing military discipline and massive resources to the effort.

Image source: Manhattan Project

Oak Ridge site selected for uranium production

Sep 19, 1942

A vast tract of land in eastern Tennessee was chosen for large-scale uranium enrichment facilities. Oak Ridge grew into a secret city housing tens of thousands of workers operating gaseous diffusion, electromagnetic separation, and thermal diffusion plants.

Image source: Oak Ridge, Tennessee

Oppenheimer appointed to lead weapons laboratory

Oct 1942

Physicist J. Robert Oppenheimer was selected by General Leslie Groves to direct the project's secret bomb design laboratory. Despite his left-wing associations, Oppenheimer's scientific brilliance and leadership made him the ideal choice to coordinate America's top physicists.

Image source: J. Robert Oppenheimer

Los Alamos laboratory founded in New Mexico

Nov 1942

A secret weapons laboratory was established on a remote mesa site in Los Alamos, New Mexico, acquired from the Los Alamos Ranch School. Scientists from across the country arrived with their families to design the atomic bombs in an isolated, purpose-built community.

Image source: Project Y

Hanford site selected for plutonium production

Dec 1942

The Hanford area along the Columbia River in Washington State was selected for plutonium production reactors and chemical separation plants. DuPont oversaw construction of what became one of the largest industrial complexes in the world, employing tens of thousands.

Image source: Hanford Site

First self-sustaining chain reaction at Chicago Pile-1

Dec 2, 1942

Under Enrico Fermi's direction, a team at the University of Chicago achieved the world's first controlled, self-sustaining nuclear chain reaction in a squash court beneath Stagg Field. Chicago Pile-1 proved that reactors could produce plutonium, validating a key path to an atomic bomb.

Image source: Chicago Pile-1

Testing and Deployment

Trinity nuclear test succeeds

Jul 16, 1945

At 5:29 a.m. near Alamogordo, New Mexico, the world's first nuclear explosion lit up the desert sky as the plutonium implosion device known as 'the Gadget' detonated with a yield of about 20 kilotons. The successful Trinity test confirmed the implosion design and opened the atomic age.

Truman informed of the atomic bomb at Potsdam

Jul 24, 1945

President Truman casually informed Soviet leader Joseph Stalin at the Potsdam Conference that the United States possessed 'a new weapon of unusual destructive force.' Stalin, already aware through espionage, showed little surprise, foreshadowing the postwar nuclear rivalry.

Image source: Potsdam Conference

Potsdam Declaration calls for Japan's surrender

Jul 26, 1945

President Harry Truman, British Prime Minister Winston Churchill, and Chinese leader Chiang Kai-shek issued the Potsdam Declaration demanding Japan's unconditional surrender or face 'prompt and utter destruction.' Japan rejected the ultimatum, setting the stage for the atomic bombings.

Image source: Potsdam Declaration

USS Indianapolis delivers Little Boy components

Jul 30, 1945

The heavy cruiser USS Indianapolis delivered the uranium core and components for the Little Boy bomb to Tinian Island in the Pacific. Days later, after leaving port, the ship was sunk by a Japanese submarine, resulting in one of the worst disasters in U.S. Navy history.

Image source: USS Indianapolis (CA-35)

Atomic bombing of Hiroshima

Aug 6, 1945

Colonel Paul Tibbets piloted the B-29 bomber Enola Gay, which dropped the uranium gun-type bomb Little Boy on Hiroshima, Japan. The explosion killed approximately 70,000 people instantly and tens of thousands more from radiation and injuries, devastating the city and shocking the world.

Image source: Atomic bombings of Hiroshima and Nagasaki

Soviet Union declares war on Japan

Aug 8, 1945

As promised at Yalta, the Soviet Union declared war on Japan and launched a massive invasion of Japanese-held Manchuria. The swift Soviet offensive, combined with the atomic bombings, shattered Japan's hopes for a negotiated peace through Moscow.

Image source: Soviet invasion of Manchuria

Atomic bombing of Nagasaki

Aug 9, 1945

Major Charles Sweeney flew the B-29 Bockscar, which dropped the plutonium implosion bomb Fat Man on Nagasaki after the primary target, Kokura, was obscured by clouds. The blast killed roughly 40,000 people immediately, compounding Japan's crisis and prompting surrender deliberations.

Japan announces surrender, ending World War II

Aug 15, 1945

Emperor Hirohito announced Japan's acceptance of the Potsdam terms in a radio broadcast, and the formal surrender was signed aboard the USS Missouri on September 2, 1945. World War II ended, with the atomic bombings widely credited with hastening Japan's capitulation.

Image source: Surrender of Japan

Aftermath and Legacy

Smyth Report released to the public

Aug 12, 1945

Physicist Henry DeWolf Smyth's official account of the Manhattan Project, 'Atomic Energy for Military Purposes,' was released days after the bombings. It provided the public with the first detailed explanation of the project's science and organization while withholding classified details.

Image source: Smyth Report

Operation Crossroads nuclear tests at Bikini Atoll

Jul 1, 1946 - Jul 25, 1946

The United States conducted a pair of nuclear tests at Bikini Atoll in the Pacific to assess the effects of atomic weapons on warships. The Able and Baker tests, witnessed by international observers and media, demonstrated the growing power and reach of the nuclear arsenal.

Image source: Operation Crossroads

McMahon Act creates Atomic Energy Commission

Aug 1, 1946

The Atomic Energy Act of 1946, sponsored by Senator Brien McMahon, transferred control of atomic energy from the military to a civilian agency, the Atomic Energy Commission. The act established a framework for both continued weapons development and peaceful nuclear applications.

Image source: United States Atomic Energy Commission

Soviet Union tests its first atomic bomb

Aug 29, 1949

The Soviet Union detonated RDS-1 ('First Lightning') at Semipalatinsk, Kazakhstan, ending the American nuclear monopoly years earlier than expected. The device was based partly on stolen Manhattan Project designs, ushering in the nuclear arms race of the Cold War.

Image source: RDS-1

Espionage revelations: Klaus Fuchs arrested

Feb 1950

British physicist Klaus Fuchs confessed to passing Manhattan Project secrets to the Soviet Union during his time at Los Alamos. His espionage, along with information from other spies like Theodore Hall, significantly accelerated the Soviet atomic program.

Image source: Klaus Fuchs

First Soviet hydrogen bomb test

Nov 1, 1952

The United States detonated Ivy Mike, the first full-scale thermonuclear weapon, at Enewetak Atoll, yielding over 10 megatons. The test demonstrated the enormous destructive potential of fusion weapons, escalating the arms race begun by the Manhattan Project.

Image source: Ivy Mike

Castle Bravo test exceeds expectations

Mar 1, 1954

The Castle Bravo test at Bikini Atoll produced a yield of 15 megatons, more than double predictions, spreading radioactive fallout over inhabited islands and a Japanese fishing vessel. The disaster drew global attention to the dangers of atmospheric nuclear testing.

Image source: Castle Bravo

Oppenheimer security clearance revoked

Apr 27, 1954

Following a contentious security hearing amid Cold War fears and rivalries within the scientific establishment, J. Robert Oppenheimer's security clearance was revoked. The decision effectively ended his government career and became a symbol of the era's anti-communist persecution.

Image source: Oppenheimer security clearance hearing

Partial Test Ban Treaty signed

Aug 5, 1963

The United States, Soviet Union, and United Kingdom signed the Limited Test Ban Treaty, prohibiting nuclear explosions in the atmosphere, outer space, and underwater. The treaty responded to decades of fallout concerns dating back to the Manhattan Project era.

Image source: Partial Nuclear Test Ban Treaty

Non-Proliferation Treaty enters into force

Mar 5, 1970

The Treaty on the Non-Proliferation of Nuclear Weapons came into effect, aiming to prevent the spread of nuclear weapons beyond the five recognized nuclear powers. It represented a global attempt to contain the proliferation risks unleashed by the Manhattan Project.

Image source: Treaty on the Non-Proliferation of Nuclear Weapons

Key Facts

The Manhattan Project began in 1939 after Albert Einstein and Leo Szilard warned President Roosevelt that Nazi Germany might develop an atomic bomb.
J. Robert Oppenheimer served as scientific director of the Los Alamos Laboratory in New Mexico, where the bombs were designed and assembled.
Major production facilities were located at Oak Ridge, Tennessee (uranium enrichment) and Hanford, Washington (plutonium production).
On July 16, 1945, the first successful nuclear test, code-named 'Trinity,' took place in New Mexico.
Atomic bombs were dropped on Hiroshima on August 6, 1945, and Nagasaki on August 9, 1945, leading to Japan's surrender and the end of World War II.

Source

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