When in 1939, the general public became aware of the Einstein–Szilard letter that urged the US government to initiate the Manhattan project, for the development of nuclear weapons, Einstein was credited for foreseeing the destructive power of the atom with his mass–energy equivalence formula. Einstein played an active role in the development of US nuclear weapons by being an advisor to the research that ensued; this was in contrast to the common belief that his role was limited to only signing a letter. During this time, the public linked Einstein with Oppenheimer, who then happened to be the scientific director of the Manhattan project.