World War II drew to an abrupt conclusion with the detonation of two nuclear weapons. Had the bombs not gone off, millions on both sides of the conflict would have perished. And the war would have continued for years.
In fact, had the bombs failed to detonate, the Allies were prepared to launch Operation Downfall, the invasion of mainland Japan. And Downfall was itself split into two massive ops: Operation Olympic and Operation Coronet. War planners anticipated millions of deaths, due primarily to the religion of militaristic Shintoism promulgated by the Japanese leadership.
Commander A.F. Birch (left), shown numbering the bomb codenamed "Little Boy" unit L-11, before loading it on trailer in Assembly Bldg. #1, prior to it being loaded aboard the B-29 Superfortress bomber "Enola Gay", on the base of the 509th Composite Group at Tinian Island in the Marianas Islands in 1945. Physicist Dr. Norman Ramsey stands at right - he would later go on to win the Nobel Prize in Physics in 1989. (U.S. National Archives)