On June 17, 1943, President Franklin D. Roosevelt’s secretary of war, Henry Stimson, phones then-Missouri Senator Harry S. Truman and politely asks him not to make inquiries about a defense plant in Pasco, Washington.
World War II was in full swing in 1943 and Truman was chairing a Senate committee on possible war profiteering committed by American defense plants. In the process of investigating war-production expenditures, Truman stumbled upon a suspicious plant in the state of Washington and asked the plant managers to testify in front of the committee. Unbeknownst to Truman, this particular plant was secretly connected with a program to develop an atomic bomb—”the Manhattan Project.” When Stimson, one of a handful of people who knew about the highly classified Manhattan Project, heard about Truman’s line of questioning, he immediately acted to prevent the Missouri senator from blowing the biggest military secret in world history.
On June 17, Truman received a phone call from Stimson, who told him that the Pasco plant was “part of a very important secret development.” Fortunately, Stimson did not need to explain further: Truman, a veteran and a patriot, understood immediately that he was treading on dangerous ground. Before Stimson could continue, Truman assured the secretary “you won t have to say another word to me. Whenever you say that [something is highly secret] to me that’s all I want to hear. If [the plant] is for a specific purpose and you think it’s all right, that’s all I need to know.” Stimson replied that the purpose was not only secret, but “unique.”
America’s secret development of the atomic bomb began in 1939, with then-President Franklin Roosevelt’s support. Even after Truman became Roosevelt’s fourth-term vice president in 1944, the project remained such a tightly controlled secret that Roosevelt did not even inform Truman that it existed. Only after Roosevelt died from a stroke, in early April 1945, did Stimson inform Truman of the nature of the Manhattan Project. The night Truman was sworn in as Roosevelt’s successor he noted in his diary that Stimson told him the U.S. was “perfecting an explosive great enough to destroy the whole world.”
On April 24, 1945, Stimson and the Army general in charge of the project, Leslie Groves, gave President Truman a full briefing on the development status of the atomic bomb. Before the year was out, the new president would be faced with a decision: whether or not to use the most powerful weapon then known to man.