After nearly a quarter-century of atomic silence, on May 11, 1998, India detonated three nuclear devices at an underground testing site, followed by two more tests two days later.
India said the tests, known as "Operation Shatki," involved both fission and fusion designs. They were carried out in the desert state of Rajasthan, close to the Pakistani border.
Pakistan responded two weeks later by conducting five of its own nuclear tests on May 28 in the southwestern province of Baluchistan.
India said the Pakistani tests proved the need for its own. "They have vindicated our policy," Indian Prime Minister Atal Bihari Vajpayee said. "They have confirmed our doubts. India is ready to meet any challenge."
The United States immediately imposed sanctions on both India and Pakistan.
Having confirmed each possesses a bomb, the two nuclear-armed countries have focused on developing and testing missile systems since then, even as they engage in peace talks over the disputed Kashmir region.
In December 2004, Pakistan tested a surface-to-surface ballistic missile capable of hitting targets deep inside India. Later that month, India successfully hit a test target with a new surface-to-surface missile with a range of 180 miles, Reuters reported.
India started its nuclear power program in 1958. The country of more than 1 billion people acquired dual-use technologies under U.S. President Eisenhower's "Atoms for Peace" nonproliferation program, which aimed to encourage the civilian use of nuclear technologies in exchange for assurances they would not be used for military purposes, according to the Federation of American Scientists.
Under the program, India acquired a 40-megawatt research reactor from Canada and heavy water -- used to control nuclear fission -- from the United States.
In 1964, India commissioned a reprocessing facility at Trombay, which was used to separate out the plutonium produced by the research reactor. The plutonium was used in India's first nuclear test on May 18, 1974, which the country claimed was for peaceful purposes.
The weapons effort had entered high gear after the South Asian
nation was soundly defeated in a 1962 war with China. A growing
concern over China's nuclear weapons capabilities and a desire
to be recognized as the dominant power in the region spurred India's
nuclear growth, according to the World Nuclear Association.
But the 1974 test helped spur historic rival Pakistan to gear
up its nuclear program. This new threat, which came to include
weapons delivery systems that can reach deep into India, served
as a further impetus to India's atomic effort.
detonated five nuclear devices on May 11-13, 1998. Analysts at
the Lawrence Livermore Laboratory determined that, based on seismic
and other data, India had tried to detonate a thermonuclear device
but the second stage of the two-stage bomb failed to ignite.
According to Joseph Cirincione at the Carnegie Endowment for International Peace, India has produced enough weapons-grade plutonium for 50-90 nuclear weapons and a smaller but unknown quantity of weapons-grade uranium.
India has insisted it has nuclear weapons for deterrence only and will only use them in retaliation if deterrence fails.
Although a member of the International Atomic Energy Agency, India has not signed the Comprehensive Test Ban Treaty or the nuclear Non-Proliferation Treaty.
Four of its 13 nuclear reactors are subject to IAEA safeguards.