Manhattan Project

President Franklin Delano Roosevelt receives a letter from Albert Einstein warning about Nazi Germany's attempts to develop an atomic weapon.

Albert Einstein sends a letter to President Franklin D. Roosevelt emphasizing the significance of studying chain reactions and the potential development of powerful bombs.

In response to the Einstein-Szilard letter, President Roosevelt assembles a group of civilian and military experts to investigate the potential military applications of uranium fission.

President Roosevelt establishes the NDRC under Vannevar Bush, absorbing the Uranium Committee.

Winston Churchill approves the Tube Alloys project, becoming the first national leader to endorse a nuclear weapons program.

The first meeting of the S-1 project took place on December 18, 1941, sponsored by the OSRD. The project was dedicated to the research and development of fission weapons on a full scale.

The Manhattan Project, which led to the development of the atomic bomb, began in 1942.

President Roosevelt gives approval for the development of an atomic bomb on January 19, 1942. Arthur Compton establishes the Metallurgical Laboratory (Met Lab) at the University of Chicago.

On May 18, 1942, Gregory Breit resigned from coordinating physics research on fast neutron phenomena, prompting Arthur H. Compton to appoint J. Robert Oppenheimer to take over the leadership role.

On June 18, 1942, the Army Corps of Engineers formally establishes the Manhattan District, a crucial step in the development of the atomic bomb during World War II.

The Manhattan Engineering District, also known as the Manhattan Project, is established with James C. Marshall as District Engineer by Major General Eugene Reybold.

On September 17, 1942, US Army Brigadier General Leslie Groves, who was still a Colonel until September 23, was appointed as the head of the Manhattan Engineer District, which was responsible for the development of the atomic bomb.

On September 19, 1942, General Leslie Groves approved Oak Ridge, Tennessee as a secret site for uranium enrichment, a crucial step in the Manhattan Project's efforts to develop the atomic bomb.

Colonel Leslie Groves is promoted to brigadier general and becomes the director of the Manhattan Project. The Military Policy Committee, consisting of key officials, is created to oversee the project.

The Manhattan Project is granted permission to use the highest wartime priority rating by the War Production Board.

Under Secretary of War Robert P. Patterson authorizes the acquisition of land in Tennessee for Site X, which will later become the Oak Ridge laboratory and production site.

On November 16, 1942, construction of the Chicago Pile-1 (CP-1), the world's first experimental nuclear reactor, commenced at the University of Chicago under the Manhattan Project's research on nuclear fission.

The Military Policy Committee, based on Groves and Conant's advice, opts to bypass the pilot plant phase and move directly to large-scale production for plutonium, electromagnetic, and gaseous diffusion projects.

On November 25, 1942, General Groves chose Los Alamos, New Mexico as the site for the bomb laboratory, known as Project Y, with J. Robert Oppenheimer appointed as the laboratory director.

On December 1, 1942, after 17 days of work, Enrico Fermi’s group completes Chicago Pile-1, containing uranium oxide, uranium metal, and graphite. Fermi halts construction when a critical configuration is reached.

On December 2, 1942, Enrico Fermi and his team of scientists achieved the first self-sustained nuclear chain reaction in Chicago, a crucial milestone in the development of nuclear weapons.

The Los Alamos laboratory is officially established on April 1, 1943.

In 1943, J. Robert Oppenheimer invited John von Neumann to contribute to the Manhattan Project. Von Neumann played a role in the hydrodynamics and implosion design for an atomic bomb.

The first nuclear reactor, Chicago Pile-1, achieves a self-sustaining reaction at the University of Chicago under the leadership of Enrico Fermi, just one month after construction began.

On July 4, 1944, J. Robert Oppenheimer reveals Emilio Segre’s measurements on the high spontaneous fission rate of reactor-produced plutonium to the Los Alamos staff. This discovery leads to a significant shift in research priorities and strategies within the Manhattan Project.

Otto Frisch conducts the Dragon experiment where a U-235 hydride slug is dropped through a barely subcritical U-235 hydride assembly, creating the world's first assembly critical through prompt neutrons alone.

Harry S. Truman was inaugurated as President after the death of Franklin D. Roosevelt and was briefed about the Manhattan Project.

The Target Committee of the Manhattan Project chooses Kyoto, Hiroshima, Kokura, and Niigata as potential cities to drop the atomic bomb during World War II.

Nazi Germany surrenders to Allied powers, signifying the end of World War II in Europe. Additionally, a 100-ton test explosion takes place at Alamogordo, New Mexico.

The Gadget, the first atomic test device, successfully detonated on July 16, 1945, at the Trinity Site in New Mexico, marking a significant milestone in the development of nuclear weapons.

President Harry S. Truman discloses to Soviet leader Joseph Stalin that the United States possesses atomic weapons, with Stalin showing little surprise due to prior espionage knowledge.

President Truman orders the use of atomic bombs.

A typhoon approaching Japan on August 1st prevents the launching of an attack with the atomic bomb Little Boy. The weather conditions require several days to clear before the mission can proceed.

The B-29 Enola Gay drops the Little Boy uranium-235 bomb on Hiroshima, causing widespread destruction and casualties.

The implosion model plutonium bomb, known as Fat Man, is dropped on Nagasaki, Japan during World War II.

On August 10, 1945, President Truman ordered that no additional atomic bombs could be used without his express authority, stating his reluctance to wipe out more people. This decision halted further atomic bombings.

General Leslie Groves, in charge of the Manhattan Project, halts the shipment of materials for a third atomic bomb without consulting higher authorities due to concerns about sending ingredients overseas. This decision is made as U-235 needed for a second bomb is not available until December.

Bernard Baruch unveils the American proposal for global supervision of atomic research on June 14, 1946.

Operation Crossroads kicks off with the detonation of Shot Able, a plutonium bomb, at Bikini Atoll on July 1, 1946.

The Manhattan Project concluded on August 25, 1947, after years of operation. It was a significant endeavor that forever changed the course of history with its development of the atomic bomb.

The Soviet Union conducts its first atomic bomb test near Semipalatinsk, Asia. The RDS-1 explosion yields 22 kilotons of TNT, similar to the bombs dropped on Hiroshima and Nagasaki.