September: Enrico Fermi suggests to Edward Teller that an atomic bomb might heat deuterium sufficiently to kindle a full-scale thermonuclear reaction. 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'ssupport 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
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
June 5: U.S. Secretary of State George Marshall announces aid plan for Europe. US
July: U.S. Chargé d'affaires in Moscow George Kennanoutlines 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.
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. Trumandisapproves. 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
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 Strausswrites to President Truman urging him to give highest priority to H-bomb development [hydrogen bomb decision] . US
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
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
March: The Royal Air Force and the Strategic Air Commandbegin 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
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
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 Tammare 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
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
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
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
October 10: Limited Nuclear Test Ban Treaty goes into effect.