The name Hiroshima is so tied to the atomic bomb that it's hard to imagine there were other possible targets.
But in early 1945, the U.S. was still months away from building its first bomb and certainly didn't know what to hit.
"Should it be a city? Should it be a military installation? Should you be just displaying the bomb, without killing anybody?" These are questions that were yet to be decided, says Alex Wellerstein, a historian at the Stevens Institute of Technology.