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.
Pakistan and weapons of mass destruction
Pakistan is one of nine states to possess nuclear weapons. Pakistan began development of nuclear weapons in January 1972 under Prime Minister Zulfikar Ali Bhutto, who delegated the program to the Chairman of the Pakistan Atomic Energy Commission (PAEC) Munir Ahmad Khan with a commitment to having the bomb ready by the end of 1976. Since PAEC, consisting of over twenty laboratories and projects under nuclear engineer Munir Ahmad Khan, was falling behind schedule and having considerable difficulty producing fissile material, Abdul Qadeer Khan was brought from Europe by Bhutto at the end of 1974. As pointed out by Houston Wood, Professor of Mechanical & Aerospace Engineering, University of Virginia, Charlottesville, in his article on gas centrifuges, "The most difficult step in building a nuclear weapon is the production of fissile material"; as such, this work in producing fissile material as head of the Kahuta Project was pivotal to Pakistan developing the capability to detonate a nuclear bomb by the end of 1984.