He was also instrumental in overseeing the Manhattan Project, as his obit in the New York Times in 1950 makes clear: "When he was in his late seventies Mr. Stimson was the civilian administrative head of a victorious army of more than 10,000,000, the largest ever raised by the United States. It was in this post that he was largely responsible for bringing to an abrupt end over Hiroshima and Nagasaki the violence that had frustrated his diplomacy in the Nineteen Thirties when he was President Hoover's Secretary of State. Mr. Stimson later disclosed that he had not hesitated in recommending to the recently sworn in President Truman the first use of the atomic bomb.
" 'My chief purpose was to end the war in victory with the least possible cost in the lives of the men in the armies which I had helped to raise,' Mr. Stimson wrote in the February, 1947, issue of Harper's magazine. 'In the light of the alternatives which, on a fair estimate, were open to us, I believe that no man in our position and subject to our responsibilities, holding in his hand a weapon of such possibilities for accomplishing this purpose and saving those lives, could have failed to use it and afterward looked his countrymen in the face.' "