The Manhattan Project: Making the Atomic Bomb

No Turning Back: Final Decisions and Presidential Approval

The S-1 Executive Committee met to consider the Lewis report on December 9, 1942, just weeks after Allied troops landed in North Africa. Most of the morning session was spent evaluating the controversial recommendation that only a small electromagnetic plant be built. Lewis and his colleagues based their recommendation on the belief that Lawrence could not produce enough uranium-235 to be of military significance. But since the calutron could provide enriched samples quickly, the committee supported the construction of a small electromagnetic plant. Conant disagreed with the Lewis committee's assessment, believing that uranium had more weapon potential than plutonium. And since he knew that gaseous diffusion could not provide any enriched uranium until the gaseous diffusion plant was in full operation, he supported the one method that might, if all went well, produce enough uranium to build a bomb in 1944. During the afternoon, the S-1 Executive Committee went over a draft Groves had prepared for Bush to send to the President. It supported the Lewis committee's report except that it recommended skipping the pilot plant stage for the pile. After Conant and the Lewis committee met on December 10 and reached a compromise on the electromagnetic method, Groves' draft was amended and forwarded to Bush. ²⁸

On December 28, 1942, President Roosevelt approved the establishment of what ultimately became a government investment in excess of $2 billion, $.5 billion of which was itemized in Bush's report submitted on December 16. The Manhattan Project was authorized to build full-scale gaseous diffusion and plutonium plants and the compromise electromagnetic plant, as well as heavy water production facilities. In his report, Bush reaffirmed his belief that bombs possibly could be produced during the first half of 1945 but cautioned that an earlier delivery was unlikely. No schedule could guarantee that the United States would overtake Germany in the race for the bomb, but by the beginning of 1943 the Manhattan Project had the complete support of President Roosevelt and the military leadership, the services of some of the nation's most distinguished scientists, and a sense of urgency driven by fear. Much had been achieved in the year between Pearl Harbor and the end of 1942.

No single decision created the American atomic bomb project. Roosevelt's December 28 decision was inevitable in light of numerous earlier ones that, in incremental fashion, committed the United States to pursuing atomic weapons. In fact, the essential pieces were in place when Roosevelt approved Bush's November 9, 1941, report on January 19, 1942. At that time, there was a science organization at the highest level of the federal government and a Top Policy Group with direct access to the President. Funds were authorized, and the participation of the Corps of Engineers had been approved in principle. In addition, the country was at war and its scientific leadership-as well as its President-had the belief, born of the MAUD report, that the project could result in a significant contribution to the war effort. Roosevelt's approval of $500 million in late December 1942 was a step that followed directly from the commitments made in January of that year and stemmed logically from the President's earliest tentative decisions in late 1939.

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