Query: Project Y's goal was to invent the first nukes.

Relevant passages:
Project Y <=SEP=> The Los Alamos Laboratory , also known as Project Y , was a secret laboratory established by the Manhattan Project and operated by the University of California during World War II . Its mission was to design and build the first atomic bombs . Robert Oppenheimer was its first director , from 1943 to December 1945 , when he was succeeded by Norris Bradbury . For scientists freely to discuss their work while preserving security , the laboratory was located in a remote part of New Mexico . The wartime laboratory occupied buildings that had once been part of the Los Alamos Ranch School .   The development effort initially concentrated on a gun-type fission weapon using plutonium called Thin Man . In April 1944 , the Los Alamos Laboratory determined that the rate of spontaneous fission in plutonium bred in a nuclear reactor was too great due to the presence of plutonium-240 and would cause a predetonation , a nuclear chain reaction before the core was fully assembled . Oppenheimer then reorganized the laboratory and orchestrated an all-out and ultimately successful effort on an alternative design proposed by John von Neumann , an implosion-type nuclear weapon , which was called Fat Man . A variant of the gun-type design known as Little Boy was developed using uranium-235 .   Chemists at the Los Alamos Laboratory developed methods of purifying uranium and plutonium , the latter a metal that only existed in microscopic quantities when Project Y began . Its metallurgists found that plutonium had unexpected properties , but were nonetheless able to cast it into metal spheres . The laboratory built the Water Boiler , an aqueous homogeneous reactor , the third reactor in the world to become operational . It also researched the Super , a hydrogen bomb that would use a fission bomb to ignite a nuclear fusion reaction in deuterium and tritium .   The Fat Man design was tested in the Trinity nuclear test in July 1945 . Project Y personnel formed pit crews and assembly teams for the bombing of Hiroshima and Nagasaki and participated in the bombing as weaponeers and observers . After the war ended , the laboratory supported the Operation Crossroads nuclear tests at Bikini Atoll . A new Z Division was created to control testing , stockpiling and bomb assembly activities , which were concentrated at Sandia Base . The Los Alamos Laboratory became Los Alamos Scientific Laboratory in 1947 .

Nuclear weapon <=SEP=> A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions , either fission ( fission bomb ) or a combination of fission and fusion ( thermonuclear weapon ) . Both reactions release large quantities of energy from relatively small amounts of matter . The first test of a fission ( `` atomic '' ) bomb released the same amount of energy as approximately 20,000 tonTNT . The first thermonuclear ( `` hydrogen '' ) bomb test released the same amount of energy as approximately 10 e6tonTNT . A thermonuclear weapon weighing little more than 2400 lb can produce an explosive force comparable to the detonation of more than 1.2 e6tonTNT . A nuclear device no larger than traditional bombs can devastate an entire city by blast , fire , and radiation . Nuclear weapons are weapons of mass destruction , and their use and control have been a major focus of international relations policy since their debut .   Nuclear weapons have been used twice in war , both times by the United States against Japan near the end of World War II . On August 6 , 1945 , the U.S. Army Air Forces detonated a uranium gun-type fission bomb nicknamed `` Little Boy '' over the Japanese city of Hiroshima ; three days later , on August 9 , the U.S. Army Air Forces detonated a plutonium implosion-type fission bomb codenamed `` Fat Man '' over the Japanese city of Nagasaki . The bombings resulted in the deaths of approximately 200,000 civilians and military personnel from acute injuries sustained from the explosions . The ethics of the bombings and their role in Japan 's surrender are subjects of debate .   Since the atomic bombings of Hiroshima and Nagasaki , nuclear weapons have been detonated over two thousand times for testing and demonstration . Only a few nations possess such weapons or are suspected of seeking them . The only countries known to have detonated nuclear weapons -- and acknowledge possessing them -- are ( chronologically by date of first test ) the United States , the Soviet Union ( succeeded as a nuclear power by Russia ) , the United Kingdom , France , the People 's Republic of China , India , Pakistan , and North Korea . Israel is also believed to possess nuclear weapons , though , in a policy of deliberate ambiguity , it does not acknowledge having them . Germany , Italy , Turkey , Belgium and the Netherlands are nuclear weapons sharing states . South Africa is the only country to have independently developed and then renounced and dismantled its nuclear weapons .   The Treaty on the Non-Proliferation of Nuclear Weapons aims to reduce the spread of nuclear weapons , but its effectiveness has been questioned , and political tensions remained high in the 1970s and 1980s . Modernisation of weapons continues to occur .