1945

US

April 25: Two weeks into his presidency, President Truman is briefed on the Manhattan Project, the U.S. wartime effort to build an atomic bomb. US

May 7: Germany surrenders to Allies in WWII ending the war in Europe.

July 16: U.S. detonates the first A-bomb near Alamogordo, New Mexico. Called the "Trinity" test, it explodes with a force equivalent to 18,000 tons of TNT. US

July 25: U.S. General Carl Spaatz, Commander of the Strategic Air Force in the Pacific, receives directive to drop atomic bomb. US

August 6: The "Little Boy" A-bomb explodes 1,900 feet above Hiroshima with a force equivalent to 12,500 tons of TNT. By the end of the year, bomb-related deaths in Japan total 140,000. US

August 9: The "Fat Man" A-bomb explodes at 1,650 feet over Nagasaki with a yield equivalent to 22,000 tons of TNT. 70,000 die in Nagasaki by the end of 1945 from the effects of the bomb. US

September 20: U.S. Joint Chiefs of Staff embrace "first-strike" atomic warfare policy. US

October: At the Los Alamos scientific laboratory in New Mexico, physicist Edward Teller seeks Robert Oppenheimer's support on a full tilt effort to build a hydrogen bomb. Oppenheimer refuses. US

October 18: Lavrentii Beria, head of the Soviet secret police and in charge of the Soviet nuclear program, is provided top-secret details on the U.S. plutonium bomb by a spy working inside Los Alamos. USSR

November 23: The USSR concludes a secret agreement with Czechoslovakia granting the Soviet Union exclusive rights to all uranium mined within Czechoslovakia. USSR

December 24: U.S. Embassy in Moscow warns of an all-out effort by USSR to build atomic bomb. US

1946

February 9: Joseph Stalin gives a speech at the Bolshoi Theater which marks a deterioration in relations with the U.S. USSR

February 22: U.S. Chargé d'affaires in Moscow George Kennan sends historic 8,000 word telegram to the State Department. It analyzes Soviet foreign policy in alarming terms. US

February 16: Columbia faculty, including physicist Isidor Rabi, urges President Truman to stop production of atomic bombs. US

March 5: Winston Churchill delivers "iron curtain" speech at Fulton, Missouri.

April 18: The secret, three-day Super Conference at , New Mexico examines feasibility of developing the hydrogen bomb. US

April: Soviet scientist Iulii Khariton chooses Sarov/Arzamas as the secret location for Soviet weapons lab. USSR

June 14: British physicist Klaus Fuchs leaves Los Alamos, New Mexico to return to England.

July: U.S. conducts atomic tests at Bikini Atoll in the Pacific. US

August 1: President Truman signs Atomic Energy Act which establishes the Atomic Energy Commission. US

September 5: FBI questions U.S. scientist Robert Oppenheimer [Oppenheimer Hearings] about his contacts with a Communist, Professor Haakon Chevalier. US

November 10: Team of Soviet scientists, headed by Igor Kurchatov, begins assembly of first full-scale nuclear reactor. USSR

December 25: Soviet scientists achieve nuclear chain reaction, one of the first steps in building the atomic bomb. USSR

December 31: Soviet scientists review espionage accounts of U.S. physicist Edward Teller's "classical super," his design for the hydrogen bomb. USSR

1947

June 5: U.S. Secretary of State George Marshall announces aid plan for Europe. US

July: U.S. Chargé d'affaires in Moscow George Kennan outlines a policy of containment of Soviet expansion. US

September 28: British physicist Klaus Fuchs meets with his agent Alexander Feklisov in London. Fuchs describes certain structural characteristics of the superbomb.

October: Joint Chiefs of Staff declare that 150 "Nagasaki type" bombs will suffice to defend the U.S. and defeat the USSR. Stockpile of weapons is still small (20-50) but growing. US

December 3: The British philosopher and outspoken pacifist, Bertrand Russell, calls for preventive war against USSR.

1948

January 7: U.S. and Great Britain revoke wartime pact on nuclear cooperation.

February 25: Soviet forces occupy Prague. USSR

March 13: British physicist Klaus Fuchs gives his agent Alexander Feklisov a detailed description of the "classical super", a design to build the H-bomb.

April: Atomic Energy Commission begins "Operation Sandstone" at Eniwetok Atoll in the Pacific to test the improved designs of fission bombs. US

May 5: President Truman is briefed on the Joint Chiefs of Staff's nuclear war plan. Dubbed "Halfmoon," the plan calls for dropping 50 atomic bombs on 20 Russian cities. Truman disapproves. US

June 7: Reactor A at Chelyabinsk reaches full criticality, enabling the USSR to produce plutonium. USSR

June 24: USSR blocks rail and road connections to West Berlin. USSR

June: Soviet physicist Igor Tamm enlists his graduate student Andrei Sakharov to study fusion problem. USSR

July: Soviet physicist Andrei Sakharov begins development of "Layer Cake" concept for hydrogen bomb. USSR

October 19: General Curtis LeMay assumes command of the Strategic Air Command. US

1949

January: Soviet physicist Andrei Sakharov moves to Arzamas, the secret weapons lab. USSR

February: Secret negotiations between the USSR and Western allies begin to solve Berlin crisis.

February 27: Plutonium separation begins at reactor in Chelyabinsk. USSR

March: The first General Curtis LeMay war plan for the Strategic Air Command envisions attacks on 70 Soviet cities with 133 bombs. US

May 15: Communists win election in Hungary.

July: U.S. physicist Edward Teller rejoins the staff at Los Alamos, New Mexico. US

August 29: First Soviet atomic bomb [first Soviet Test] is exploded in Kazakhstan. USSR

September 3: A U.S. weather plane flying off the coast of Siberia picks up evidence of radioactivity. US

September 23: President Truman announces explosion of first Soviet atomic bomb. US

October: U.S. government approves program to expand production of uranium and plutonium. US

October 29: General Advisory Committee to the Atomic Energy Commission argues against a crash program to develop the hydrogen bomb [hydrogen bomb decision]. US

November 25: Atomic Energy Commissioner Lewis Strauss writes to President Truman urging him to give highest priority to H-bomb development [hydrogen bomb decision] . US

1950

January 27: In London British physicist Klaus Fuchs confesses to being a Soviet spy.

January 31: President Truman announces his decision to develop the hydrogen bomb [hydrogen bomb decision]. US

February 5: Twelve leading U.S. physicists, including Hans Bethe, speak out against President Truman's decision to build the hydrogen bomb. US

February: Joint Intelligence Committee predicts build up of Soviet atomic arsenal and possible attack against U.S. "at earliest possible moment". US

February 24: U.S. Joint Chiefs of Staff request "all out effort to build H-bomb." US

March 1: U.S. physicist Klaus Fuchs is tried at the Old Bailey in London for being a Soviet spy.

April 7: National Security Council document NSC-68 warns of surprise attack by Soviet Union once "it has sufficient atomic capability." US

June 16: U.S. mathematicians Stanislaw Ulam and Cornelius Everett conclude their calculations on "classical super", Edward Teller's H-bomb design. The plan appears not to work. US

June 25: North Korea invades South Korea.

September 30: The NSC-68 document that warns of surprise attack by the Soviet Union is adopted as statement of policy. Defense spending is increased by more than 350%. US

November 30: President Truman confirms during press conference that use of nuclear weapons in Korea had been under consideration. US

December 16: With the Chinese army having entered the Korean war, President Truman declares national emergency and signs order to increase armed forces by 3.5 million men. US

1951

January: U.S. mathematician Stanislaw Ulam proposes radically new design for H-bomb. Edward Teller embraces and refines the concept. US

January 12: President Truman establishes the Federal Civil Defense Administration. US

April 4: U.S. physicist Edward Teller submits report on new design for H-bomb. US

April 5: U.S. Joint Chiefs of Staff order atomic retaliation against air bases in case of "a major attack" against UN forces in Korea. US

May 9: U.S. conducts the "George" test in the Pacific: a large fission bomb that triggers the first thermonuclear reaction. US

September 17: U.S. physicist Marshall Holloway is named leader of H-bomb project. Edward Teller leaves Los Alamos, New Mexico shortly afterwards. US

September 24: Soviet Union conducts its second nuclear test, an improved plutonium bomb. USSR

December: A four-man team at RAND begins to study the likely effects of the H-bomb. US

1952

March: The Royal Air Force and the Strategic Air Command begin flying photographic and radar reconnaissance missions over Soviet Union.

September: A second weapons lab is established in Livermore, California. US

October 3: First British nuclear test, code-named "Hurricane," is conducted off the northwest coast of Australia.

November 1: "Mike," the first H-bomb, is successfully tested at Eniwetok in the Pacific. US

December: President-elect Eisenhower and staff develop "New Look" defense policy relying primarily on power of atomic forces. US

1953

January: In his final State of the Union address, President Truman declares nuclear war impossible for "rational men." US

March 5: Soviet leader Joseph Stalin dies. USSR

March 20: Nikita Khrushchev becomes first secretary of Communist party. USSR

June 26: Nikita Khrushchev authorizes arrest of Lavrentii Beria, head of the secret police and the Soviet bomb project. USSR

July: In a "Foreign Policy" article U.S. physicist Robert Oppenheimer calls for greater openness in atomic policy debate. US

July 27: Armistice is signed ending the war in Korea.

August: General Edmundson leads "Operation Big Stick." The mission requires him to take twenty B-36s, armed with nuclear weapons, to Okinawa in Japan. US

August 8: Soviet Premier Georgii Malenkov announces that USSR possesses hydrogen bomb. USSR

August 12: First test of Soviet thermonuclear device (Andrei Sakharov's "Layer Cake") takes place. USSR

November 7: Lawyer William L. Borden sends letter to FBI Director J. Edgar Hoover accusing U.S. physicist Robert Oppenheimer [Oppenheimer Hearings] of being a Soviet spy. US

December 3: President Eisenhower orders a "blank wall" be placed between U.S. physicist Robert Oppenheimer [Oppenheimer Hearings] and atomic secrets. US

December 23: Atomic Energy Commission sends letter with charges to U.S. physicist Robert Oppenheimer[Oppenheimer Hearings] . US

December 23: Nikita Khrushchev authorizes the execution of Lavrentii Beria, the former head of Soviet secret police and the Soviet bomb project. USSR

1954

January 7: In his State of the Union address, President Eisenhower claims that 2,200 employees have been fired as security risks. US

January 12: Secretary of State John Foster Dulles announces administration policy of "massive retaliation'" in response to Communist attacks. US

February: Soviet physicists Andrei Sakharov and Igor Tamm are presented with the Hero of Socialist Labor and the Stalin Prize for their work on the "Layer Cake." USSR

March 1: "Bravo" hydrogen bomb test in the Pacific, at Bikini Atoll. US

March 4: U.S. physicist Robert Oppenheimer [Oppenheimer Hearings] sends written response to the Atomic Energy Commission charges against him. US

April 12: U.S. physicist Robert Oppenheimer's security hearings [Oppenheimer Hearings] begin at Atomic Energy Commission. US

June 28: Atomic Energy Commissioners vote against U.S. physicist Robert Oppenheimer [Oppenheimer Hearings] and uphold withdrawal of security clearance. US

September 14: 44,000 Soviet troops take part in a military exercise involving

the dropping of an atomic bomb. USSR

1955

May 10: The Soviet Union unexpectedly accepts UN proposal for nuclear disarmament. USSR

May 14: Warsaw Pact is signed.

June 15: President Eisenhower evacuates the White House in Operation Alert air raid drill. US

July 18: Big Four summit begins in Geneva. President Eisenhower unveils his proposal for "open skies" and an exchange of military secrets. US

August 8: In Geneva, the first UN conference begins on the peaceful use of atomic energy.

September 6: U.S. delegate Harold Stassen announces that America no longer supports UN plan calling for complete nuclear disarmament. US

November 22: First Soviet thermonuclear bomb [Soviet Two Stage Weapon Test] is dropped in Kazakhstan from an aircraft in test, with a force equivalent to 1.6 megatons of TNT. USSR

1956

February 14: Nikita Khrushchev attacks Stalin and "cult of personality." USSR

March: U.S. explains its opposition to nuclear disarmament at UN stating that atomic weapons are a "powerful deterrent to war." US

1960

December: The Joint Strategic Target Planning Staff complete SIOP 62. This war plan calls for the launch of more than 3,000 nuclear weapons--including hundreds of hydrogen bombs--to attack in the first few hours of conflict 1,000 separate targets in the Communist bloc. US

May 3: Mass protest against the civil defense drill Operation Alert takes place in City Hall Park of New York city. US

1963

October 10: Limited Nuclear Test Ban Treaty goes into effect.