The Need to develop an A-bomb In 1939, the Nazis were rumored to be developing an atomic bomb. The United States initiated its own program under the Army Corps of Engineers in June 1942.

General Leslie R. Groves General Leslie R. Groves directed the Manhattan Project. Groves established three large engineering and production centers at remote U.S. sites The Clinton Engineer Works at Oak Ridge, Tenn.; the Hanford Engineer Works in eastern Washington State; and Project Y, a code-named site 100 miles north of Albuquerque at Los Alamos, N.M.

University of Chicago Italian physicist Enrico Fermi managed the University of Chicago reactor, called Chicago Pile 1 (CP-1). On the afternoon of December 2, 1942, it happened. Under the abandoned west stands of Stagg Field, the first controlled nuclear reaction occurred.

Oak Ridge, Tennessee Scientists now had to create the fuel for an atomic bomb. The Oak Ridge facility separated the nuclear fuel from natural uranium

Hanford, Washington The Hanford Engineer Works produced plutonium To build the facility, the townships of Richland, White Bluffs, and Hanford vanished. As at Oak Ridge, 1,500 people were relocated in the process. Close to a half-million acres were purchased for more than $5.1 million by the spring of 1943.

Los Alamos, New Mexico At Los Alamos, an international team of scientists and engineers labored around the clock to create the first atomic weapons.

Known as "the hill," Los Alamos produced two bombs. One, nicknamed “Little Boy” The second bomb, “Fat Man”

J. Robert Oppenheimer Theoretical physicist Oppenheimer, who would direct Los Alamos research, identified top scientists and engineers from universities nationwide.

Trinity The first atomic test device was nicknamed Trinity

The First Atomic Device On Monday, July 16, 1945, at 5:29:45 a.m., the first atomic device was detonated

The World's First Atomic Blast J. Robert Oppenheimer, who had directed the project, said: "We waited until the blast had passed, walked out of the shelter and then it was extremely solemn. We knew the world would not be the same. A few people laughed, a few people cried. Most people were silent. “I remembered the line from the Hindu scripture, 'Now I am become Death, the destroyer of worlds.' I suppose we all thought that, one way or another." - J. Robert Oppenheimer

The decision to drop President Truman was attending the Potsdam Conference at the time of the test. He was informed via telegraph that the test was a success Truman and his advisors decided not to tell the other world leaders at the conference any details about the weapon. Truman proceeded with military plans for an invasion Great Britain and the Soviet Union approved the Potsdam declaration which warned Japan of an invasion if they do not surrender. No mention of the bomb was made. Japan announced that they would ignore the declaration

Little Boy and Fat Man Little Boy was the first nuclear weapon used in warfare. It exploded approximately 1,800 feet over Hiroshima, Japan, on the morning of August 6, 1945, with a force equal to 13,000 tons of TNT. Immediate deaths were between 70,000 to 130,000. Fat Man was the second nuclear weapon used in warfare. Dropped on Nagasaki, Japan, on August 9, 1945, Fat Man devastated more than two square miles of the city and caused approximately 45,000 immediate deaths.