Question: When were nuclear weapons developed?

Timeline of nuclear weapons development

This timeline of nuclear weapons development is a chronological catalog of the evolution of nuclear weapons rooting from the development of the science surrounding nuclear fission and nuclear fusion. In addition to the scientific advancements, this timeline also includes several political events relating to the development of nuclear weapons. The availability of intelligence on recent advancements in nuclear weapons of several major countries (such as United States and the Soviet Union) is limited because of the classification of technical knowledge of nuclear weapons development.
1930−1950
1933 - Leó Szilárd realizes the concept of the nuclear chain reaction, although no such reaction was known at the time. He invented the idea of an atomic bomb in 1933 while crossing a London street. He patented it in 1934. (British patent 630,726)
1938 - December - German Chemists, Otto Hahn and Fritz Strassman detect barium after bombarding uranium with neutrons. This is correctly interpreted by Lise Meitner and her nephew Otto Robert Frisch as nuclear fission.
1939 - January - Otto Robert Frisch experimentally confirms Otto Hahn and Fritz Strassman's discovery of nuclear fission.
1939 - April - Nazi Germany begins the German nuclear energy project.
1939 - October - US President Franklin Delano Roosevelt receives the Einstein–Szilárd letter and authorizes the creation of the Advisory Committee on Uranium. The Uranium Committee has its first meeting on October 21, and $6,000 was budgeted for conducting neutron experiments.
1940 - April - MAUD Committee (Military Application of Uranium Detonation) established by Henry Tizard to investigate feasibility of an atomic bomb.
1940 - May - The paper which Dr. Yoshio Nishina of Nuclear Research Laboratory of Riken and Professor of Chemical Institute, Faculty of Science, Imperial University of Tokyo, Kenjiro Kimura presented to Physical Review,[1][2] showed that they had produced Neptunium-237 by exposing Uranium oxide (U3O8) to fast neutrons for more than 50 hours.
1940 - July - The paper explaining that Dr. Yoshio Nishina and Kenjiro Kimura discovered symmetric fission on the previously described test, appeared in Nature.[3][4][5] The LibreTexts libraries based upon work supported by the National Science Foundation says, "Multiple combinations of symmetric fission products are possible for fission chain reactions."[6] And, again, it as fission product yield, is known that the higher the energy of the state that undergoes nuclear fission is more likely a symmetric fission.
1941 - February - Plutonium discovered by Glenn Seaborg and Arthur Wahl.
1941 - October - President Roosevelt receives MAUD report on the design and costs to develop a nuclear weapon. Roosevelt approves project to confirm MAUD's finding
1942 - April - Joseph Stalin was first informed of the efforts to develop nuclear weapons based on a letter sent to him by Georgii Flerov pointing out that there was nothing being published on nuclear fission since its discovery, and the prominent physicists likely involved had not been publishing at all. This urged the Soviet Union to start a nuclear weapons program.
1942 - July - The Heereswaffenamt (HWA, Army Ordance Office) relinquishes control of the German nuclear energy project to the Reichsforschungsrat (RFR, Reich Research Council), essentially making it only a research project with objectives far short of making a weapon.
1942 - July through September - A summer conference at University of California, Berkeley is convened by physicist Robert Oppenheimer and discusses the design of a fission bomb. Edward Teller introduces the "Super" hydrogen bomb as a major discussion point.
1942 - August through November - The Manhattan Project is established under command of General Leslie Groves. "Site X" is chosen in Tennessee, for isotopic separation of uranium-235 from natural uranium, and will later become Oak Ridge National Laboratory. "Hanford Site is chosen in Washington, for making plutonium in nuclear reactors. "Site Y" is chosen in New Mexico, for bomb design and manufacture, and will later become Los Alamos National Laboratory.
1943 - March - The Japanese Committee on Research in the Application of Nuclear Physics, chaired by Yoshio Nishina concludes in a report that while an atomic bomb was feasible, it would be unlikely to produce one during the war. Japan then concentrated on research into radar.
1943 - April - Introductory lectures begin at Los Alamos, which later are compiled into The Los Alamos Primer.
1943 - August - Quebec Agreement signed by President Roosevelt and Winston Churchill. A team of British scientists join the Manhattan Project, including Klaus Fuchs.
1944 - April - Emilio Segrè discovers that the spontaneous fission rate of plutonium is too high to be used in a gun-type fission weapon. Leads to change in priority to the design of an implosion-type nuclear weapon.
1945 - May - Nazi Germany formally surrenders to Allied Powers, marking the end of World War II in Europe.
1945 - July 16 - The first nuclear explosion, the Trinity test of an implosion-type plutonium-based nuclear weapon known as "the gadget", near Alamogordo, New Mexico.
1945 - August 6 - "Little Boy", a gun-type uranium-235 weapon, is dropped on Hiroshima, Japan.
1945 - August 9 - "Fat Man", an implosion-type plutonium-239 weapon, is dropped on Nagasaki, Japan.
1945 - August - The Smyth Report is published detailing the efforts of the Manhattan Project.
1945 - August - Surrender of Japan to the Allied Powers.
1946 - January - The Atomic Energy Act of 1946 takes effect, officially turning over the Manhattan Project to the United States Atomic Energy Commission.
1946 - June - First meeting of the United Nations Atomic Energy Commission is held.
1946 - Soviet Union rejects the Baruch Plan.
1949 - August - The Soviet Union conducts its first atomic test, First Lightning (nicknamed Joe 1 by the Americans).
1950−1970
1951 - China and the Soviet Union sign an agreement whereby China would supply uranium ore in exchange for technical assistance in producing nuclear weapons.
1952 - October - The United Kingdom conducts Operation Hurricane, the first test of a British nuclear weapon. The plutonium implosion-type nuclear weapon was detonated in a lagoon between the Montebello Islands, Western Australia.
1952 - November - The United States test the first fusion bomb, "Ivy Mike".
1953 - The first nuclear-tipped rockets are deployed by the United States. The MGR-1 Honest John is such as example.
1953 - August - The Soviet Union conducts its first test of a hydrogen bomb, nicknamed Joe 4 by the Americans.
1954 - March - The United States detonates its first deliverable thermonuclear weapons at Bikini Atoll, Marshall Islands. One device had a yield almost three times as large as expected, leading to the worst radiological disaster in US history.
1956 - France establishes a secret committee for the Military Applications of Atomic Energy.
1956 - The Pakistan Atomic Energy Commission is established. This commission is responsible for the development of both the nuclear reactors and nuclear weapons in Pakistan.
1957 - July - The International Atomic Energy Agency is founded.
1958 - The United States and the United Kingdom sign the 1958 US-UK Mutual Defence Agreement. This is a bilateral treaty on nuclear weapons cooperation signed after the United Kingdom successfully tested a hydrogen bomb during Operation Grapple.
1960 - February - France successfully tests a nuclear weapon, called "Gerboise bleue", in the French Sahara.
1961 - The Israeli Prime Minister David Ben-Gurion informed the Canadian Prime Minister John Diefenbaker that a pilot plutonium-separation plant would be built at Dimona, the location of the nuclear reactor built with the aid of France and Great Britain. Intelligence would indicate from this and other information that Israel intended to produce nuclear weapons.
1961 - October - The Soviet Union detonates Tsar Bomba, the largest, most powerful nuclear weapon ever detonated.
1963 - August - The Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water opens for signatures. The treaty limited nuclear weapons tests to underground detonations.
1964 - October - China successfully tests an atomic bomb at Lop Nur.
1965 - January - The Soviet Union detonates Chagan as part of their Nuclear Explosions for the National Economy series to study the peaceful use of nuclear explosions.
1967 - June - China successfully tests a hydrogen bomb.
1967 - December - Japan, under Prime Minister Eisaku Satō, adopts the Three Non-Nuclear Principles.
1968 - July - The Nuclear Non-Proliferation Treaty opens for signatures. This treaty is intended to limit the spread of nuclear weapons. To date, 189 countries have signed the treaty, including the five permanent members of the UN Security Council. Only India, Israel, Pakistan, and North Korea have not signed the treaty (as sovereign states).
1970−1990
1972 - Zulfikar Ali Bhutto launched Pakistan's atomic program by making Munir Ahmad Khan as the program head.
1974 - May - India tests its first nuclear device, "Smiling Buddha", at Pokhran.
1974 - May - Pakistan's Project-706 is established under command of General Zahid Ali Akbar.
1986 - September - Mordechai Vanunu divulges secrets about the Israeli nuclear weapons program to The Sunday Times in London.
1990−present
1991 - South Africa signs the Nuclear Non-Proliferation Treaty; they also announce that from 1979 to 1989, they had built and then dismantled a number of nuclear weapons.
1991 - June - The Brazilian-Argentine Agency for Accounting and Control of Nuclear Materials is established to play an active role in verifying the pacific use of nuclear materials that could be used for the manufacture of nuclear weapons in Argentina and Brazil.
1996 - January - France performs its last nuclear tests to date on Moruroa atoll.
1998 - May - India tests five more nuclear weapons as part of Operation Shakti at the Pokhran test site. This was India's second round of nuclear weapons testing.
1998 - May - Pakistan detonates five high-enriched uranium nuclear weapons in the Chagai Hills. A sixth nuclear test, at Kharan, was a plutonium device.
2003 - North Korea announces that it has several nuclear explosives.
2005 - August - In Iran, Ayatollah Ali Khamenei issued a fatwa forbidding the production, stockpiling and use of nuclear weapons.
2006 - October - North Korea tests a nuclear weapon for the first time.
2016 - January - North Korea Hydrogen bomb is 'tested' and confirmed by North Korea leader Kim Jong-Un
2017 - September - North Korea conducted its seventh nuclear test with a yield between fifty and two hundred fifty kilotons.
See also
History of Nuclear Weapons
Nuclear Weapons
Nuclear Fission
Nuclear Fusion