Pokhran-II (Operation Shakti) was a series of five nuclear weapon tests conducted by India in May 1998. The bombs were detonated at the Indian Army's Pokhran Test Range in Rajasthan. It was the second instance of nuclear testing conducted by India, after the first test, code-named Smiling Buddha, was conducted in May 1974.

The test consisted of five detonations, the first of which was a high yield fusion bomb while the remaining four were fission bombs. One fusion and two fission bombs were detonated on 11 May 1998 and two more fission bombs were detonated two days later on 13 May 1998. The tests were collectively called Operation Shakti, and the five nuclear bombs were designated as Shakti-I through to Shakti-V.

The tests achieved their main objective of giving India the capability to build fission and thermonuclear weapons with yields up to 200 kilotons. Then chairman of the Indian Atomic Energy Commission described each one of the explosions to be equivalent to several tests carried out over the years by various nations. The Indian government convened a press conference to announce the tests and declared India as a full-fledged nuclear state. As a consequence of the tests, United Nations Security Council Resolution 1172 was enacted and economic sanctions were imposed by a number of countries including Japan and the United States.

Efforts towards building a nuclear bomb, infrastructure, and research on related technologies have been undertaken by India since the end of Second World War. The origins of India's nuclear program can be traced back to 1945 when nuclear physicist Homi Bhabha established the Tata Institute of Fundamental Research (TIFR) with the aid of Tata Group. After Indian Independence, the Atomic Energy Act was passed on 15 April 1948, that established the Indian Atomic Energy Commission (IAEC). In 1954, Department of Atomic Energy (DAE) was established which was responsible for the atomic development programme and was allocated a significant amount of the defence budget in the subsequent years. In 1956, the first nuclear reactor became operational at Bhabha Atomic Research Centre (BARC), becoming the first operating reactor in Asia. In 1961, India commissioned a reprocessing plant to produce weapon grade Plutonium. In 1962, India was engaged in a war with China and with China conducting its own nuclear test in 1964, it accelerated India's need to develop nuclear weapons.

With two reactors operational in early 1960s, research progressed in learning and development of know-how to manufacture nuclear weapons. With the unexpected deaths of then Prime Minister Nehru in 1964 and Bhabha in 1966, the programme slowed down. The incoming prime minister Lal Bahadur Shastri appointed physicist Vikram Sarabhai as the head of the nuclear programme and the direction of the programme changed towards utilizing nuclear energy peaceful purposes rather than military development.

After Shastri's death in 1966, Indira Gandhi became the prime minister and work on the nuclear programme resumed. The design work on the bomb proceeded under physicist Raja Ramanna, who continued the nuclear weapons technology research after Bhabha's death in 1966. The project employed 75 scientists and progressed in secrecy. During the Indo-Pakistani War, the U.S. government sent a carrier battle group into the Bay of Bengal in an attempt to intimidate India, who were aided by the Soviet Union, who responded by sending a submarine armed with nuclear missiles. The Soviet response demonstrated the deterrent value and significance of nuclear weapons to India. After India gained military and political initiative over Pakistan in the war, the work on building a nuclear device continued. The hardware began to be built in early 1972 and the Prime Minister authorized the development of a nuclear test device in September 1972.

On 18 May 1974, India tested a implosion-type fission device at the Indian Army's Pokhran Test Range under the code name Smiling Buddha. The test was called as a Peaceful Nuclear Explosive (PNE) and the yield was estimated to be between 6 and 10 kilotons.

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While India continued to state that the test was for peaceful purposes, it encountered opposition from many countries. The Nuclear Suppliers Group (NSG) was formed in reaction to the Indian tests to check international nuclear proliferation. The technological embargo and sanctions affected the development of India's nuclear program. It was crippled by the lack of indigenous resources and dependence on imported technology on certain areas. Though India declared to the International Atomic Energy Agency (IAEA) that India's nuclear program was intended only for peaceful purposes, preliminary work on a fusion bomb was initiated. In the aftermath of the state emergency in 1975 that resulted in the collapse of the government, the program continued under M.R. Srinivasan, but made slow progress. Though the nuclear program did not receive much attention from incoming Prime Minister Morarji Desai at first, the program gained impetus when Ramanna was appointed to the Ministry of Defence.

With the discovery of Pakistan's clandestine atomic bomb program, India realized that it was very likely to succeed in its project in a few years. With the return of Indira Gandhi in 1980, the nuclear program gained momentum. Two new underground shafts were constructed at the Pokhran test range by 1982 and Gandhi approved further nuclear tests in 1982. But the decision was reversed owing to pressure from the United States as it might end-up in nuclear brinkmanship with Pakistan and potential foreign policy implications. But work continued towards weaponizing the nuclear bomb under V. S. R. Arunachalam and the Indian missile programme was launched under A. P. J. Abdul Kalam. Ramanna pushed forward with a Uranium enrichment program and despite the sanctions, India imported heavy water required as a neutron moderator in the nuclear reactors, from countires like China, Norway and Soviet Union through a middleman. Though Rajiv Gandhi, who became the Prime Minister in 1984, supported technological development and research, he was skeptical about nuclear testing as he believed it would result in further technological alienation from the developed countries. Dhruva, a new reactor with a capability to produce larger quantities of weapon grade material, was commissioned at BARC in 1985. Other components for a nuclear fusion bomb were developed during the time with capabilities to air drop nuclear weapons. In late 1985, a study group commissioned by the Prime Minister outlined a plan for the production of 70 to 100 nuclear warheads and a strict no first use policy.

In 1989, V.P. Singh formed the government, which collapsed within two years and this period of instability caused a snag in the nuclear weapons programme. Foreign relations between India and Pakistan severely worsened when India accused Pakistan of supporting the Insurgency in Jammu and Kashmir. During this time, the Indian Missile Program succeeded in the development of the Prithvi missiles. India decided to observe the temporary moratorium on the nuclear tests for fear of inviting international criticism. The NSG decided in 1992 to require full-scope IAEA safeguards for any new nuclear export deals, which effectively ruled out nuclear exports to India.

Though India had stock-piled material and components to be able to construct a dozen nuclear fission bombs, the deliverance mechanism was still under development. With the successful testing of Agni missile and successful trials involving dropping of similar bombs without fissionable material from bomber aircraft in 1994, the weaponization became successful. With the Comprehensive Nuclear-Test-Ban Treaty under discussion and global pressure pushing India to sign, then Indian Prime Minister Narasimha Rao ordered preparations for further nuclear tests in 1995. Based on the direction of the director of DAE R. Chidambaram, S. K. Sikka was tasked with the development of a thermo-nuclear fusion device. In August, K. Santhanam, the chief technical adviser of DRDO, was appointed the director for carrying out the tests. While water was being pumped out of the shafts constructed more than ten years earlier, American spy satellites picked up the signs. With pressure from US President Bill Clinton, the test never progressed.

With Rao's term ending in 1996, the next two years saw multiple governments being formed. Atal Bihari Vajpayee, who was a strong advocate of nuclear weaponization, came to power following the 1998 general elections. Vajpayee had earlier declared that if re-voted to power, his government would induct nuclear weapons and declare India's might to gather respect. Soon after assuming power in March 1998, Vajpayee organized a discussion with Abdul Kalam and Chidambaram to conduct nuclear tests. On 28 March 1998, he asked to make preparations for a test.

The Indian Intelligence Bureau had been aware of the capability of the United States spy satellites in detecting Indian test preparations. Therefore, the tests required complete secrecy and the 58th Engineer Regiment of the Indian Army Corps of Engineers was tasked with preparing the test sites without being detected. Work was mostly done during night, and equipment was returned to the original place during the day to give the impression that it was never moved. Bomb shafts were dug under camouflage netting and the dug-out sand was shaped like natural sand dunes. Cables and sensors were either covered with sand or concealed using native vegetation. A select group was involved in the detonation process with all personnel required to wear uniforms to preserve the secrecy of the tests. They were given pseudo-names and they traveled in smaller groups to avoid detection.

Scientists and engineers of BARC, the Atomic Minerals Directorate for Exploration and Research (AMDER), and DRDO were involved in the development and assembly of the bombs. Three laboratories of the DRDO were involved in designing, testing and producing components for the bombs, including the detonators, the implosion and high-voltage trigger systems. These were also responsible for systems engineering, aerodynamics and safety. The bombs were transported moved from BARC at 3 am on 1 May 1998 to Bombay airport, then flown in an Indian Air Force's AN-32 aircraft to Jaisalmer Airport. It was then transported to Pokhran in an army convoy of four trucks, and this required three trips. The devices were delivered to the device preparation building, which was designated as Prayer Hall'.

Following were the main personnel involved in the testing:

• Chief Coordinators :
  • A.P.J. Abdul Kalam, scientific adviser to the defence minister and head of the DRDO
  • R. Chidambaram, chairman of the Atomic Energy Commission and the Department of Atomic Energy
• Defence Research & Development Organization (DRDO):
  • K. Santhanam, director of test site preparations
• Bhabha Atomic Research Centre (BARC) :
  • Anil Kakodkar, director
  • Satinder Kumar Sikka, lead for thermonuclear weapon development
  • M. S. Ramakumar, Director of Nuclear Fuel and Automation Manufacturing Group; lead for manufacture of nuclear components
  • D.D. Sood, director of Radiochemistry and Isotope Group; director of nuclear materials acquisition
  • S.K. Gupta, Solid State Physics and Spectroscopy Group; director of device design and assessment
  • G. Govindraj, associate director of Electronic and Instrumentation Group; director of field instrumentation

The test was organized into two groups to be fired separately, with all devices in a group fired at the same time. Five nuclear devices were tested during the operation.
Group-I:

• Shakti I: Two stage thermonuclear device with fusion boosted primary, test design yield 45 kt, but designed for up to 200 kt deployed yield
• Shakti II: A light-weight plutonium implosion fission device yielding 12 kt and intended as a warhead that could be delivered by bomber or missile
• Shakti III: An experimental linear implosion fission device that used reactor-grade plutonium, yielding 0.3 kt

Group-II:

• Shakti IV: A 0.5 kt experimental fission device
• Shakti V: A 0.2 kt Thorium/U-233 experimental fission device

An additional, sixth device (Shakti VI) was developed but not detonated. The first test was planned on 11 May. The high yield thermonuclear device was placed in a shaft code named White House, which was approximately 230 metres [m] (750 ft) deep, the fission bomb was placed in a 150 metres (490 ft) deep shaft code named Taj Mahal, and the first sub-kiloton device in shaft Kumbhkaran. The first three devices were placed in their respective shafts on 10 May. The first device to be placed was the sub-kiloton device, which was sealed by the army engineers by 8:30 PM. The thermonuclear device was lowered and sealed by 4 AM on the next day with the fission device being placed by 7:30 AM. The shafts were L-shaped, with a horizontal chamber used for the test devices. The timing of the tests was pursuant to the local weather conditions, and the test sequence was initiated in the afternoon. Santhanam, in-charge of the test site, handed over the site to M. Vasudev, the range safety officer, who was responsible for verifying the test indicators. After the safety clearance, the countdown system was activated and at 3:45 PM IST, the three devices were detonated simultaneously. On 13 May, at 12.21 PM IST, two sub-kiloton devices (Shakti IV and V) were detonated. Due to their very low yield, these explosions were not detected by any seismic station.

Having tested weaponized nuclear warheads, India became the sixth country to join the nuclear club. Shortly after the tests, Prime Minister Vajpayee appeared before the press corps and made the following short statement:

Today, at 15:45 hours, India conducted three underground nuclear tests in the Pokhran range. The tests conducted today were with a fission device, a low yield device and a thermonuclear device. The measured yields are in line with expected values. Measurements have also confirmed that there was no release of radioactivity into the atmosphere. These were contained explosions like the experiment conducted in May 1974. I warmly congratulate the scientists and engineers who have carried out these successful tests.

On 13 May 1998, India declared the series of tests to be over after this.

News of the tests were greeted with jubilation and large-scale approval by general public in India. The Bombay Stock Exchange registered significant gains. The media praised the government for its decision and advocated the development of an operational nuclear arsenal for the country's armed forces. The opposition led by Indian National Congress criticized the Vajpayee administration for carrying out the series of nuclear tests, accusing the government of trying to use the tests for political ends rather than to enhance the country's national security.

By the time India had conducted tests, the country had a total of $44bn in loans in 1998, from the IMF and the World Bank. The industrial sectors of the Indian economy were likely to be hurt by sanctions with the foreign companies, which had invested heavily in India, facing consequences of impending sanctions. The Indian government announced that it had factored the economic response and was willing to take the consequences.

The United States issued a statement condemning India and threatened economic sanctions. The intelligence community felt humiliated for its failure to detect the preparations for the test. In keeping with its preferred approach to foreign policy in recent decades, and in compliance with the 1994 anti-proliferation law, the United States imposed economic sanctions on India. The sanctions on India consisted of cutting off all assistance to India except humanitarian aid, banning the export of certain defense material and technologies, ending American credit and credit guarantees to India, and requiring the US to oppose lending by international financial institutions to India. The United States held talks with India over the issue of India becoming a part of the CTBT and NPT and pressurized to rollback India's nuclear program. India did not accede to the request stating that it was not consistent with her national security interest.

Canada criticized India's actions. Japan imposed economic sanctions which included freezing all new loans and grants except for humanitarian aid. Few other nations also imposed sanctions on India, primarily in the form of suspension of foreign aid and government-to-government credit lines. China stated that it was seriously concerned about the tests which are not favorable to the peace and stability in the region and called for the international community to pressurize India to cease the development of nuclear weapons. It further rejected claims of India's stated rationale of needing nuclear capabilities to counter a Chinese threat as unfounded. However, permanent members of the United Nations Security Council such as the United Kingdom, France, and Russia refrained from making any statements condemning the tests.

Pakistan issued a statement blaming India for instigating a nuclear arms race in the region with Prime Minister Nawaz Sharif stating that his country will take appropriate action. Pakistan carried out six nuclear tests under the codename Chagai-I on 28 May 1998 and Chagai-II on 30 May 1998. Pakistan's leading nuclear physicist, Pervez Hoodbhoy, held India responsible for Pakistan's nuclear test experiments. Pakistan's subsequent tests invited similar condemnation and economic sanctions. On June 6, the UN Security Council adopted Resolution 1172, condemning the Indian and Pakistani tests.

The Government of India declared 11 May as National Technology Day in India to commemorate the first of the five successful nuclear weapon tests that were carried out on 11 May 1998. The day is celebrated by giving awards to various individuals and industries in the field of science and technology.

Parmanu: The Story of Pokhran is a 2018 Bollywood movie was based on the nuclear tests. War and Peace is a documentary by Anand Patwardhan, which details the events of the tests.

• India and weapons of mass destruction
• Pokhran-I