The United States and weapons of mass destruction

United States of America

Nuclear program start date	21 October 1939
First nuclear weapon test	16 July 1945
First fusion weapon test	1 November 1952
Last nuclear test	23 September 1992
Largest yield test	15 Mt (1 March 1954)
Total tests	1,054 detonations
Peak stockpile	32,040 warheads (1967)
Current stockpile (usable and not)	4,670 total (2016)
Current strategic arsenal	1,890 methods of delivery (including ICBMs, Bombers, and including MIRVed warheads on SLBMs ) (2016)
Cumulative strategic arsenal in megatonnage	≈490 (2016)
Maximum missile range	13,000 km (8,078 mi) (land) 12,000 km (7,456 mi) (sub)
NPT party	Yes (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 deployed nuclear weapons in the world, after Russia.

Nuclear weapons have been used twice in combat: two nuclear weapons were used by the United States against Japan during World War II in the atomic bombings of Hiroshima and Nagasaki. Altogether, the two bombings killed 120,000 people and injured another 130,000 while devastating hundreds or thousands of military bases, factories, and cottage industries.