It's June of 1942, and President Roosevelt just picked up Winston Churchill from the airport in his car. (Doesn't that sound like the start of a bad joke?)
While driving to Roosevelt's family mansion, Hyde Park, the two hash out a bunch of stuff about the war, including the importance of building an atomic bomb, and especially before the Germans can. Churchill pledges Britain's cooperation.
Leslie Groves, an army colonel built like a bulldog, is informed that he's been assigned to oversee the building of some kind of super-bomb. He's disappointed because he wanted to get out of D.C. to serve abroad in combat. One of the reasons he's been selected is because he did such a great job building the Pentagon—on time, and on budget. (That's impressive. Seriously.)
The bomb project is now officially dubbed the Manhattan Project, because that's where its first offices are located. Someone in D.C. needs to learn how to come up with better names…
Even though he gets promoted to General for his troubles, Groves is still moping about the job he's been assigned because of all the uncertainty and theoretical guesswork involved.
Groves decides that despite protests about Oppenheimer's leadership skills, he wants to put Oppie in charge of the scientists working on the Manhattan Project.
The FBI protested Oppenheimer's appointment due to his past involvement with the Communist Party and friendship with people connected to the Communist movement, but Oppie insists that all of his interest in communism was a thing of the past.
Groves pulls some strings, and despite Oppenheimer's past communist interests and his failure of the army physical (due to being underweight and suffering from a chronic cough thanks to his chain-smoking habits), Oppenheimer is appointed to be in charge of the Manhattan Project.