We've been told that dropping the bomb saved lives and that Japan would have never surrendered had we not used the bomb.
The truth is, the Japanese military officials knew their defeat was at-hand and hoped to negotiate a conditional surrender to prevent more of their cities from being firebombed.* Meanwhile, Washington imposed deliberately difficult unconditional terms to perpetuate the war long enough to test the newest weapons** in the arsenal. A new extensive and expensive secret industry had been created to build these bombs and officials wanted to use them in a real war scenario to test their effectiveness.
A handful of virgin targets were off-bounds to firebomb raids and designated as primary and secondary atomic bomb targets. On August 6, 1945, Hiroshima was the primary. The skies were clear, and it was a perfect day to roll out the previously untested uranium gun weapon nicknamed, Little Boy.
After the new technology*** had been demonstrated, the Japanese conditional terms of surrender were met and credit was given to the bomb for bringing the war to a swift end.
** A long skinny uranium gun weapon nicknamed Little Boy and a bulbous beast of a bomb appropriately named Fat Man. The former, was detonated a thousand feet above the city of Hiroshima, and produced a 13.5 kiloton blast that destroyed that city. Fat Man, a plutonium implosion device, produced a 17 kiloton blast over Nagasaki three days later.
*** There were other options on the table that would have spared cities and civilian lives. It had been proposed that we simply invite Japanese officials to witness a demonstration of the awesome destructive power of the bomb. Unfortunately, the desire for real battlefield blast data outweighed the lives of hundreds of thousands of civilians.