Grateful your father made in back Stateside safe and sound. I have always wondered, as FDR was frail at Yalta, and was steamrollered by Churchill and Stalin, if he hadn't died at Warm Springs in April 1945. Germany surrendered in early May 1945, then his appearance at Potsdam when he "gave away the farm to Stalin, as far as post-war Germany's future was concerned, and then had to make the decision that Truman had to make- would a sickly and dying President and Commander-In-Chief have decided to use the atom bomb(s) to bring Japan to her knees and surrender?
I think I know one possible reason why Truman had no apparent problem in deciding to bomb Japan--He was a Captain in an Artillery Company and saw the carnage of war in 1918-first hand. So he could visualize only too clearly the great cost in American and Allied lives were we to set aside the usage of the Atom bomb, and invade Japan from the sea..
Truman was one of the last Presidents with a full set of cojones, he said what was on his mind, clearly and without obfuscation or deceit, and let the devil take the hindmost.