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United States
Location of United States
Nuclear program start date21 October 1939
First nuclear weapon test16 July 1945
First fusion weapon test1 November 1952
Last nuclear test23 September 1992
Largest yield test15 Mt (1 March 1954)
Total tests1,054 detonations
Peak stockpile32,040 warheads (1967)
Current stockpile (usable and not)6,185 total6,185
(2019)
Current strategic arsenal1,600 methods of delivery (including ICBMs, Bombers, and including MIRVed warheads on SLBMs)
(2019)
Cumulative strategic arsenal in megatonnage≈1430 (2014)
Maximum missile range13,000 km (8,078 mi) (land)
12,000 km (7,456 mi) (sub)
NPT partyYes (1968, one of five recognized powers)

The United States is known to have possessed three types of weapons of mass destruction: nuclear weapons, chemical weapons, and biological weapons. The U.S. is the only country to have used nuclear weapons in combat, when it detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki during World War II. It had secretly developed the earliest form of the atomic weapon during the 1940s under the title "Manhattan Project". The United States pioneered the development of both the nuclear fission and hydrogen bombs (the latter involving nuclear fusion). It was the world's first and only nuclear power for four years (1945–1949), until the Soviet Union managed to produce its own nuclear weapon. The United States has the second largest number of nuclear weapons in the world, after Russia.

Nuclear weapons