Video: 'The Birth of the Manhattan Project - WW2 Special'

(Monday, January 19, 1942; during World War II) — Responding to a Nov. 27, 1941, recommendation by Vannevar Bush that “an atomic bomb WAS feasible,” U.S. President Franklin D. Roosevelt, spurred on by the Dec. 7, 1941, attack on Pearl Harbor, replied today with a brief handwritten note, “V. B. OK — returned — I think you had best keep this in your own safe FDR.”

Video: 'Birth of the Bomb'

General Leslie Groves would be put in charge of the massive effort, which included the federal government seizing land in Oak Ridge, Tennessee to build a production facility housing about 75,000 workers.

Within the government, only a handful of people knew the totality of what would become known as the Manhattan Project, including a core group within the executive branch.