Basically the first half-hour of the opera is an extended...

Basically the first half-hour of the opera is an extended prologue, which is all material from the first two weeks of July 1945, ... Germany has just capitulated. Truman is meeting Stalin at Potsdam, which is where all this pressure comes from for the test to work. Oppenheimer has been in these meetings in Washington to select the target, and it's full steam ahead to Japan.