Harold C. Urey discovers deuterium (heavy hydrogen) which is present (0.014%) in all natural hydrogen compounds including water. Later contributes to U235 isotope separation.

James Chadwick proves the existence of neutrons. Not being repelled by similarly-charged particles, the neutron made an ideal "bullet" for bombarding other nuclei.

Adolf Hitler becomes chancellor of Germany. Due to anti-semitism, many prominent scientists flee central Europe. They felt Hilter's Germany would create the bomb first.

Hungarian physicist Leo Szilard realizes that, "if we could find an element which is split by neutrons, and which would emit two neutrons when it absorbs one, such an element could sustain a nuclear chain reaction."

Enrico Fermi of Italy irradiates uranium with neutrons. He believes he has produced the first transuranic element, but unknowingly achieves the world's first nuclear fission.

Leo Szilard files a patent application for the atomic bomb. The patent described the concept of using neutron induced chain reactions to create explosions.

Otto Hahn, Fritz Strassman and Lise Meitner produce Uranium nuclear fission at Germany's Kaiser Wilhelm Institute.

Albert Einstein's first letter to President Franklin Roosevelt. The letter, originally drafted by Leo Szilard states "that the element uranium may be turned into a new and important source of energy in the immediate future."

With "Operation Weiss", Germany invades Poland and World War II begins. American papers call it a Blitzkrieg or "lightening war" because of the speed and efficiency of the attack.

The University of California begins building a giant cyclotron under the direction of Ernest O. Lawrence.

The day before the bombing of Pearl Harbor, President Roosevelt authorizes the Manhattan Engineering District with $2 billion to build the atom bomb.

September 23, 1942

Colonel Leslie Groves is promoted to Brigadier-General and put in charge of the Manhattan Project. He recruits J. Robert Oppenheimer as Scientific Director.

At the University of Chicago, in a squash court under Stagg Field, Enrico Fermi and his team produce the world's first controlled and self-sustained nuclear fission reaction.

November 29, 1943

The US Military begin remodeling the B-29 bomber for the delivery of the A-bomb. Bomb's sizes are decided: "Thin Man" representing Roosevelt and "Fat Boy" for Churchill.

July 17, 1944

Important military port in the San Francisco Bay goes up in a horrific explosion killing 323 men, disintegrating two ships and an entire train. Calculations and declassified documents lead to a possible US test firing of a nuclear weapon.

Franklin Roosevelt dies, and Harry S. Truman becomes the 33rd President of the United States. April 25th, Truman is briefed about the Manhattan Project and the development of the bomb.

May 7, 1945

Soon after Adolf Hitler killed himself, German General Alfred Johl signed the unconditional surrender of all German forces on all fronts, ending tWorld War II for Europe.

The Franck Committee Report - with its request that the bomb be demonstrated to Japan before being used on civilians - is taken to Fermi, Lawrence and Oppenheimer.

July 16, 1945

Trinity Test at Alamogordo, New Mexico: exploding with a 18,000 Ton TNT equivalence.

Little Boy explodes over Hiroshima killing over 100,000 people. Three days later, Fat Man explodes over Nagasaki killing 75,000. Japan surrenders soon after.