<P> By investing heavily in breeding plutonium in early nuclear reactors and in the electromagnetic and gaseous diffusion enrichment processes for the production of uranium - 235, the United States was able to develop three usable weapons by mid-1945 . The Trinity test was a plutonium implosion - design weapon tested on 16 July 1945, with around a 20 kiloton yield . Faced with an imminent invasion of the Japanese home islands and with Japan not surrendering, President Harry S. Truman ordered the atomic raids on enemy cities . On 6 August, a uranium - gun design bomb, Little Boy, was detonated over the Japanese city of Hiroshima with an energy of about 15 kilotons of TNT, destroying nearly 50,000 buildings (including the 2nd General Army and Fifth Division headquarters) and killing approximately 70,000 people, among them 20,000 Japanese combatants and 20,000 Korean slave laborers . On 9 August, a plutonium implosion - design bomb, Fat Man, was used against the Japanese city of Nagasaki with the explosion equivalent to about 20 kilotons of TNT, destroying 60% of the city and killing approximately 35,000 people, among them 23,200--28,200 Japanese munitions workers, 2,000 Korean slave laborers, and 150 Japanese combatants . </P> <P> Between 1945 and 1990, more than 70,000 total warheads were developed, in over 65 different varieties, ranging in yield from around . 01 kilotons (such as the man - portable Davy Crockett shell) to the 25 megaton B41 bomb . Between 1940 and 1996, the U.S. spent at least $8.89 trillion in present - day terms on nuclear weapons development . Over half was spent on building delivery mechanisms for the weapon . $557 billion in present - day terms was spent on nuclear waste management and environmental remediation . </P> <P> Richland, Washington was the first city established to support plutonium production at the nearby Hanford nuclear site, to power the American nuclear weapons arsenals . It produced plutonium for use in cold war atomic bombs . </P> <P> After the end of the Cold War following the dissolution of the Soviet Union in 1991, the U.S. nuclear program was heavily curtailed, halting its program of nuclear testing, ceasing production of new nuclear weapons, and reducing its stockpile by half by the mid-1990s under President Bill Clinton . Many of its former nuclear facilities were shut down, and their sites became targets of extensive environmental remediation . Much of the former efforts towards the production of weapons became involved in the program of stockpile stewardship, attempting to predict the behavior of aging weapons without using full - scale nuclear testing . Increased funding was also put into anti-nuclear proliferation programs, such as helping the states of the former Soviet Union eliminate their former nuclear sites, and assist Russia in their efforts to inventory and secure their inherited nuclear stockpile . By February 2006, over $1.2 billion had been paid under the Radiation Exposure Compensation Act of 1990 to U.S. citizens exposed to nuclear hazards as a result of the U.S. nuclear weapons program, and by 1998 at least $759 million had been paid to the Marshall Islanders in compensation for their exposure to U.S. nuclear testing, and over $15 million was paid to the Japanese government following the exposure of its citizens and food supply to nuclear fallout from the 1954 "Bravo" test . In 1998, the country spent an estimated total of $35.1 billion on its nuclear weapons and weapons - related programs . </P>

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