After realizing that the eighteen-month timeline for building nuclear weapons capability was too ambitious, Bhabha held several meetings with US officials in secret between 1964 and 1965. In these, he explored the option of importing nuclear explosive capability, especially fissile plutonium and designs of a nuclear device, from the US Atomic Energy Commission as part of Project Plowshare. However, with the emergence of the Nuclear Nonproliferation Treaty, this option eventually closed. After Bhabha's death, dissatisfied with the NPT's refusal to meet India's security concerns, scientists at the Bhabha Atomic Research Centre and the Defence Research and Development Organization began work on the nuclear device used in the 1974 Pokhran test.