September 1 - World War II begins when the Germans invaded Poland. The official declaration of war by the British and French was made on September 3, 1939.

October 9 - Vannevar Bush, head of the National Defense Research Committee, briefs President Roosevelt and Vice President Henry A. Wallace about atomic bomb research. Roosevelt asks for further research.

December 7 - Pearl Harbor, the largest U.S. naval base in the Pacific, is attacked by Japanese warplanes commanded by Vice Admiral Chuichi Magumo. Over 2,400 people were killed in the unexpected attack.
(Photo: © Getty Images)

December 8 - President Franklin Roosevelt gives a speech to Congress and urges them to declare war on Japan. Great Britain also declared war on Japan.

December 19 - Germany and Italy declare war on the United States.

March 18 - The War Relocation Authority is established in the United States. They will gather about 120,000 Japanese Americans and taken them to internment camps. However, 17,000 Japanese Americans still sign up to fight for the United States in World War II.

June 4-5 - Battle of Midway was a turning point in the war where the United States gained a major victory against Japan.

August 7 - The United States begins the initiative on the Pacific islands, landing at Guadalcanal.

August 13 - The Manhattan Engineer District, later known as the Manhattan Project, is established in New York City.
(Photo: Atomic Energy Commission)

September 17 - Colonel Leslie R. Groves is appointed head of the Manhattan Engineer District.

November 25 - Col. Groves chooses Los Alamos, New Mexico as the bomb laboratory. J. Robert Oppenheimer is named the laboratory director.

December 28 - President Roosevelt approves the production details to begin producing atomic weapons.

September 8 - Italy surrenders to Allied forces

June 6 - Allied forces invade Normandy.
(Photo: AFP / © Getty Images)

August 7 - Vannevar Bush informs General George C. Marshall that a uranium bomb could be ready by August 1, 1945.

September - President Roosevelt and Prime Minister Winston Churchill agree to continue research on atomic technology by signing an "aide memoire."

March - Firebombing in Tokyo results with 100,000 casualties.

April 12 - President Roosevelt dies and Harry Truman is named President.
(Photo: AFP / © Getty Images)

April 27 - Four target cities are named by the Target Committee of the Manhattan Project: Kyoto, Hiroshima, Kokura, and Niigata.

May 7 - The German forces in Europe surrender.

May 23 - Firebombing in Tokyo leaves 83,000 dead.

June 6 - Secretary of War Henry Stimson advises President Truman the Interim Committee recommends keeping the atomic bomb a secret and using it without warning.

July 16 - Scientists in Los Alamos successfully test the world's first atomic bomb detonation, known as the Trinity test, in Alamogordo, New Mexico.

July 21 - President Truman orders atomic bombs to be used.

July 26 - Leaders of the United States, China, and Great Britain asks for Japan to surrender unconditionally in the Potsdam Declaration but the Japanese refuse on July 29.

August 6 - The uranium based atomic bomb named "Little Boy" was dropped on Hiroshima by the Enola Gay, a Boeing B-29 bomber, at 8:15 in the morning. Estimates vary; approximately 80,000 - 100,000 people were killed immediately.

August 8 - Russia declares war on Japan.

August 9 - The plutonium based atomic bomb, "Fat Man," is dropped on Nagasaki. The bomb's original target was Kokura but due to bad weather it was changed to Nagasaki.

August 14 - Japan surrenders.
(Photo: AFP / © Getty Images)

September 2 - The Japanese officially surrenders signing the Instrument of Surrender on the U.S.S. Missouri In Tokyo Bay.

October - Edward Teller, referred to as the "father of the hydrogen bomb," asked J. Robert Oppenheimer to help build a new hydrogen bomb but Oppenheimer refused.

December 31 - The National Defense Research Committee and the Office of Scientific Research and Development is abolished and their responsibilities are given to the Department of Defense.

Nagasaki Atomic Bomb Museum

National Atomic Museum, NM

National Testing

Children of the Manhattan Project

Atomic Archives

NHK Peace Archives