President Truman is briefed on Manhattan Project

Harry S. Truman (1884-1972) was the 33rd President of the United States of America.

Truman first learned of the Manhattan Project after the death of President Roosevelt in April of 1945, when he relinquished his role as Vice President and took the oath of office as the next president of the United States. Although he knew nothing about the project’s intricacies or nuclear politics in general before Roosevelt’s death, Truman ultimately became in charge of the most difficult moral and tactical decision of World War II: whether or not to drop the atomic bomb. His ultimate decision led to the bombings of Hiroshima and Nagasaki

America’s secret development of the atomic bomb began in 1939 with then-President Franklin Roosevelt’s support. The project was so secret that FDR did not even inform his fourth-term vice president, Truman, that it existed. (In fact, when Truman’s 1943 senatorial investigations into war-production expenditures led him to ask questions about a suspicious plant in Minneapolis, which was secretly connected with the Manhattan Project, Truman received a stern phone call from FDR’s secretary of war, Harry Stimson, warning him not to inquire further.)

When President Roosevelt died on April 12, 1945, Truman was immediately sworn in and, soon after, was informed by Stimson of a new and terrible weapon being developed by physicists in New Mexico. In his diary that night, Truman noted that he had been informed that the U.S. was perfecting an explosive great enough to destroy the whole world.

On April 24, Stimson and the army general in charge of the project, Leslie Groves, brought Truman a file full of reports and details on the Manhattan Project. They told Truman that although the U.S. was the only country with the resources to develop the bomb–eliminating fears that Germany was close to developing the weapon–the Russians could possibly have atomic weapons within four years. They discussed if, and with which allies, they should share the information and how the new weapon would affect U.S. foreign-policy decisions. Truman authorized the continuation of the project and agreed to form an interim committee that would advise the president on using the weapon

Although the war in Europe ended in May 1945, Stimson advised Truman that the bomb might be useful in intimidating Soviet leader Joseph Stalin into curtailing post-war communist expansion into Eastern Europe. On July 16, the team of scientists at the Alamogordo, New Mexico, research station successfully exploded the first atomic bomb. Truman gave Stimson the handwritten order to release when ready but not sooner than August 2 on July 31, 1945.

The first bomb was exploded over Hiroshima on August 6, 1945, and a second was dropped on Nagasaki on August 9. The Japanese quickly surrendered. Although other nations have developed atomic weapons and nuclear technology since 1945, Truman remains the only world leader to have ever used an atomic bomb against an enemy.

source: atomicheritage.org, history.com