operation downfall. there was a great documentary on the history channel 10 or so years ago called "X-DAY, the invasion of japan". i forget the exact numbers, but it was something like 1 million projected allied casualties, not to mention the toll on both the japanese military and civilian populations. there was a program put in place with manuals distributed to the japanese civilian population which gave them tips and tactics on how to ambush and stab allied servicemen to death with pointed bamboo spears, which i believe were also distributed. basically, a poor man's volkssturm, minus the panzerfaust and other quality weapons. on top of the countless lives saved on both sides, truman knew that it would have been disastrous, with political suicide being an understatement, if the american public found out that he had a way to end the war and chose not to!