Summary

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TIME PERIODS

1890s-1939:

Atomic Discoveries

1939-1942:

Early

Government Support

1942:

Difficult Choices

1942-1944:

The Uranium

Path to the Bomb

1942-1944:

The Plutonium

Path to the Bomb

1942-1945:

Bringing It All Together

1945:

Dawn of the Atomic Era

1945-present:

Postscript --

The Nuclear

Age

FINAL APPROVAL TO BUILD THE BOMB (Washington, D.C., December 1942)

Anxious as he was to get moving, Leslie Groves decided to

make one final quality control check. On November 18,

1942, Groves appointed Warren K. Lewis of the

Massachusetts Institute of Technology to head a final review

committee, comprised of himself and three DuPont

representatives. During the final two weeks of November,

the committee traveled from New York

to Chicago to Berkeley and back again through Chicago. It

endorsed the work on gaseous diffusion at Columbia,

though it made some organizational recommendations; in

fact, the Lewis committee advocated elevating gaseous

diffusion to first priority and expressed reservations about the electromagnetic

program despite an impassioned presentation by Ernest Lawrence in Berkeley. Upon

returning to Chicago, Crawford H. Greenewalt, a member of the Lewis committee, was

present at Stagg Field when CP-1 (Chicago Pile #1) first went critical. (For more on

CP-1, skip ahead to "Early Pile Design, 1942.") Significant as this moment was in the

history of physics, it came after the Lewis committee endorsed moving piles to the pilot

stage and one day after Groves instructed DuPont to move into pile design and construction.

The S-1 Executive Committee (left)

met to consider the Lewis report on

December 9, 1942. 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 Lawrence's

calutrons could provide enriched

samples quickly, the committee supported the construction of a small electromagnetic

plant. James 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 Vannevar Bush to send to President Franklin D.

Roosevelt. The draft 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

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December 10 and reached a compromise on an intermediate-scale electromagnetic plant, Groves’ draft was amended and forwarded to Bush.

On December 28, 1942, President Roosevelt approved

what ultimately became a government investment in

excess of $2 billion, $0.5 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 almost

inevitable in light of numerous earlier ones that, in

incremental fashion, committed the United States to the

pursuit of atomic weapons. In fact, the essential pieces

were in place when Roosevelt approved Bush's

November 9, 1941 report on January 19,

1942 (left). 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.