The Manhattan Project was top secret.
Secrecy proved to be a blessing in disguise. Although it dictated remote site locations, required subterfuge in obtaining labor and supplies, and served as a constant irritant to the academic scientists on the project, it had one overwhelming advantage: Secrecy made it possible to make decisions with little regard for normal peacetime political considerations. Groves knew that as long as he had the backing of the White House money would be available and he could devote his considerable energies entirely to running the bomb project. Secrecy in the Manhattan Project was so complete that many people working for the organization did not know what they were , working on until they heard about the bombing of Hiroshima on the radio. The need for haste clarified priorities and shaped decision making. Unfinished research on three separate, unproven processes had to be used to freeze design plans for production facilities, even though it was recognized that later findings inevitably would dictate changes. The pilot plant stage was eliminated entirely, violating all manufacturing practices and leading to intermittent shutdowns and endless troubleshooting during trial runs in production facilities. The inherent problems of collapsing the stages between the laboratory and full production created an emotionally charged atmosphere with optimism and despair alternating with confusing frequency.
Nothing was really revealed until the bombings of Hiroshima and Nagasaki.