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The Manhattan Project

By Andrew Kimball


Click any of these links to go straight to the page:

The Plan



Page 1


Page 2

The Scientists




The Bomb



  • Identify the main members of the Manhattan Project
  • Recognize key events in the making of the atomic bomb

After this presentation, you should be able to:

The beginnings of the atomic bomb


Government Interest


American scientists, many of them refugees from fascist regimes in Europe, took steps in 1939 to organize a project to use the newly recognized fission process for military purposes.

In the summer of 1939, Albert Einstein was persuaded by his fellow scientists to use his influence to present the military potential of an uncontrolled fission chain reaction to Pres. Franklin D. Roosevelt.The government allocated $6,000 towards research on the possibilities an uncontrolled fission chain reaction could provide.

Entering the War



After the U.S. entered World War II, the War Department was given joint responsibility for the project, because by mid-1942 it was obvious that a vast array of pilot plants, laboratories, and manufacturing facilities would have to be constructed for the assembled scientists to carry out their mission.

In September 1942 Brig. Gen. Leslie R. Groves was placed in charge of all Army activities (chiefly engineering activities) relating to the project. “Manhattan Project” became the code name for research work that would extend across the country.

By 1943, a cooperative effort commitee had been set up with Canada and Great Britain. In that same year, numerous Canadian and British scientists moved to the U.S. to join the project.

Oppenheimer & more

The Scientists

The Scientists

American physicist J. Robert Oppenheimer headed the Manhattan Project, with the goal of developing the atomic bomb.

Edward Teller was among the first recruited for the project.

Leo Szilard and Enrico Fermi built the first nuclear reactor.

Ernest Orlando Lawrence was program chief in charge of the development of the electromagnetic process of separating uranium-235 (the most impportant element in the fission process).

Other notable researchers included Otto Frisch, Niels Bohr, Felix Bloch, James Franck, Emilio Segrè, Klaus Fuchs, Hans Bethe, and John von Neumann.

How did the bomb get completed?

The Production


The Plan

Uranium-235, plutonium-239, both needed for the fission process, had to be separated from their natural companions, which required huge amounts of power and large, complex facilities. The separation of the elements occured in Oak Ridge, Tennessee and Pasco, Washington, as well as at the University of Chicago.

Before 1943, work on the design and functioning of the bomb itself was largely theoretical, based on fundamental experiments carried out at a number of different locations.

A laboratory directed by J. Robert Oppenheimer was created on an isolated mesa at Los Alamos, New Mexico. This laboratory was tasked with developing methods to reduce the fissionable products of the production plants to pure metal and fabricate the metal to required shapes.


The Production

By the summer of 1945, amounts of plutonium-239 sufficient to produce a nuclear explosion had become available from Pasco, Washington.

Weapon development and design were sufficiently advanced so that an actual field test of a nuclear explosive could be scheduled.

Elaborate and complex equipment had to be assembled to provide a complete diagnosis of success or failure. By this time the original $6,000 authorized for the Manhattan Project had grown to $2 billion.

The Trinity

The Production

The first atomic bomb was exploded at 5:30 AM on July 16, 1945, at the Alamogordo air base 120 miles south of Albuquerque, New Mexico. Oppenheimer had called the site “Trinity” in reference to one of John Donne’s Holy Sonnets.

The bomb—a plutonium implosion device called Gadget—was raised to the top of a 100-foot steel tower that was designated “Zero.” The area at the base of the tower was marked as “Ground Zero,” a term that would pass into common parlance to describe the centre of an (often catastrophic) event.

The explosion came as an intense light flash, a sudden wave of heat, and later a tremendous roar as the shock wave passed and echoed in the valley. A ball of fire rose rapidly, followed by a mushroom cloud extending to 40,000 feet. The bomb generated an explosive power equivalent to 15,000 to 20,000 tons of TNT; the tower was completely vaporized and the surrounding desert surface fused to glass for a radius of 800 yards.

How did it all go down?

The Bomb

Little Boy

The Bomb

Hiroshima was selected as the primary target because of its military value; the city served as the headquarters of the Japanese Second Army.

The following month, two other atomic bombs produced by the project, the first using uranium-235 and the second using plutonium, were dropped on the Japanese cities of Hiroshima and Nagasaki.

On August 6, 1945, at about 8:15 AM local time, a U.S. B-29 bomber released a gun assembly fission bomb—dubbed Little Boy—above Hiroshima. The weapon detonated at an altitude of 1,900 feet, and the explosive yield was estimated to be the equivalent of 15,000 tons of TNT.

Some 70,000 people were killed instantly, and by the end of the year the death toll had surpassed 100,000. Two-thirds of the city area was destroyed.

Fat Man

The Bomb

By the morning of August 9, 1945, the Soviet Union had declared war on Japan, but the Japanese government had not yet communicated its intent to surrender to the Allies.

A B-29 carrying Fat Man—a plutonium implosion bomb similar to the one used in the Trinity test—was initially dispatched to Kokura.

Thick clouds and haze over Kokura prevented the bombardier from sighting the designated aimpoint, however, and the bomber proceeded to its secondary target, the port city of Nagasaki.

At 11:02 AM Fat Man exploded at an altitude of 1,650 feet northwest of the city centre. The bomb detonated with the explosive force of 21,000 tons of TNT. An estimated 40,000 people were killed instantly, and at least 30,000 more would die from their injuries and radiation poisoning by the end of the year.

The Japanese initiated surrender negotiations the next day. By this point, Groves had notified U.S. Pres. Harry S. Truman that another bomb would be ready for delivery within a week.


A quick quiz over what you have learned.

Who was the military official put in charge of the Manhattan Project?

Audie Murphy

Dwight D. Eisenhower

Leslie Groves

Question 1/5

Niels Bohr

Robert J. Oppenheimer

Edward Teller

Question 2/5


Who was the leading scientist in the creation of the atomic bomb?




Question 3/5


What was the name of the bomb site for the July 16, 1945 test?

August 9, 1945

August 13, 1945

August 6, 1945

Question 4/5

When was the first bomb, Little Boy, dropped on Hiroshima?


August 9, 1945

July 30, 1945

August 8, 1944

Question 5/5


When was the second bomb, Fat Man, dropped on Nagasaki?

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