The so-called Smiling Buddha was the first test fission explosion by India on May 18, 1974.
On September 7, 1972, Prime Minister Indira Gandhi gave authorization to the scientists at the Bhabha Atomic Research Center (BARC) to manufacture the nuclear device they had designed and prepare it for a test. Throughout its development, the device was formally called the "Peaceful Nuclear Explosive," but it was usually referred to as the Smiling Buddha.
The head of the development team was Raja Ramanna. Other key members were P.K. Iyengar, Rajagopala Chidambaram, and Dr. Nagapattinam Sambasiva Venkatesan. The project employed no more than 75 scientists and engineers from 1967 - 1974.
The device used a high explosive implosion system developed at the DRDO Terminal Ballistics Research Laboratory (TBRL) in Chandigarh based on the American design from WWII. But the Indian design was simpler and less sophisticated than the American system. The 6 kg of Plutonium came from the CIRUS reactor at BARC. The neutron initiator was a Polonium-Beryllium type (again like those used in early U.S. bombs) code-named "Flower." The complete core was assembled in Trombay before transportation to the test site.
The fully assembled device was hexagonal, 1.25 m in diameter and weighed 1400 kg. The device was detonated at 8.05 a.m. in a shaft 107 m under the army Pokhran test range in the Thar Desert, Rajasthan. Officially the yield was reported at 20 KT, but 8 KT is more likely.
In 1975, Homi Sethna (chairman of the Atomic Energy Commission), Raja Ramanna and Nag Chaudhuri (head of the DRDO) received the Padma Vibhushan - India's second highest civilian award. Five other project members received the fourth highest award, the Padma Shri.
The CIRUS reactor used to produce the plutonium was a research reactor based on the NRX design and donated by Canada in 1960, with heavy water supplied by the US ("CIRUS" = Canada-India Reactor U.S.). The Smiling Buddha test caused a public outcry in Canada, and the Canadian government cut off exchange of nuclear materials and technology with India in the wake of the test.
India did not carry out any more nuclear tests until Operation Shakti in 1998.