United States and weapons of mass destruction
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.
U.S. nuclear weapons in Japan
In December 2015 the United States Government acknowledged officially for the first time that it had stored nuclear weapons in Okinawa prior to 1972. That U.S. nuclear weapons had been located in Okinawa had long been an open secret. The fact had been widely understood or strongly speculated since the 1960s and was subsequently revealed by the U.S. military in apparently unnoticed photographs of nuclear weapons and delivery systems on Okinawa that were declassified and released to the U.S. National Archives in 1990.