As part of the 1950s-era Atoms for Peace program, the United States actively promoted nuclear energy cooperation with India from the mid-1950s, building nuclear reactors (Tarapur), providing heavy water for the CIRUS reactor, and allowing Indian scientists to study at U.S. nuclear laboratories. When other nations joined the Nuclear Nonproliferation Treaty (NPT) in 1968, however, India refused to join the treaty on the basis that it was discriminatory. In 1974, India exploded a “peaceful” nuclear device, demonstrating that nuclear technology transferred for peaceful purposes could be used to produce nuclear weapons. As a result, the United States has refused nuclear cooperation with India for twenty-five years and has tried to convince other states to do the same.