After missing a rendezvous, Major Sweeney decided to go on the run shorthanded. For the second time, the Japanese failed to recognize the danger of the small formation and assumed it was a reconnaissance patrol. The bomb fell close to target. It may have been the most successful gratuitous bombing of all time, though the Highway of Death attack deserves mention.
Regardless of how one feels about the moral decision to launch the nuclear age by dropping the first atomic bomb on Hiroshima, it is a stretch to believe that military intellicence advised President Truman that a surrender would follow within three days. By this argument, the question of why a second bomb was dropped on Nagasaki is inherently significant to history and even to our self-identity as a uniquely moral species.
A final line from Wikipedia:
An unknown number of survivors from the Hiroshima bombing made their way to Nagasaki and were bombed again.