numbering in the tens of thousands. The delivery systems for nuclear weapons typically cost several times as much as the weapons themselves. The nuclear programme was partially slowed when Lal Bahadur Shastri became the prime minister. Shastri faced the Indo-Pakistani War of 1965. He appointed physicist Vikram Sarabhai as the head of the nuclear programme but, because of his non-violent Gandhian beliefs, Sarabhai directed it toward peaceful purposes rather than military development. In 1967, Indira Gandhi became the prime minister and work on the nuclear programme resumed with renewed vigour. Homi Sethna, a chemical engineer, played a significant role in the development of weapon-grade plutonium, while Ramanna designed and manufactured the entire nuclear device. India's first nuclear bomb project did not employ more than 75 scientists because of its sensitivity. The weapons programme was now directed towards the production of plutonium rather than uranium. In 1968–69, P. K. Iyengar visited the Soviet Union with three colleagues and toured the nuclear research facilities at Dubna, Russia. During his visit, Iyengar was impressed by the plutonium-fueled pulsed fast reactor. Upon his return to India, Iyengar set about developing plutonium reactors approved by the Indian political leadership in January 1969. The secret plutonium plant was known as Purnima, and construction began in March 1969. The plant's leadership included Iyengar, Ramanna, Homi Sethna, and Sarabhai. Sarabhai's presence indicates that, with or without formal approval, the work on nuclear weapons at Trombay had already commenced. Secrecy and test preparations, 1972–1974 In December 1971, during the Indo-Pakistani War, the U.S. government sent a carrier battle group led by the into the Bay of Bengal in an attempt to intimidate India. The Soviet Union responded by sending a submarine armed with nuclear missiles from Vladivostok to trail the US task force. The Soviet response demonstrated the deterrent value and significance of nuclear weapons and ballistic missile submarines to Indira Gandhi. India gained the military and political initiative over Pakistan after acceding to the treaty that divided Pakistan and led to the creation of Bangladesh. On 7 September 1972, near the peak of her post-war popularity, Indira Gandhi authorised the Bhabha Atomic Research Centre (BARC) to manufacture a nuclear device and prepare it for a test. Although the Indian Army was not fully involved in the nuclear testing, the army's highest command was kept fully informed of the test preparations. The preparations were carried out under the watchful