When/how did Harry Truman give the order to bomb Hiroshima?

Question

Am I correct in assuming that Truman and only Truman had the authority to order the bombing of Hiroshima? After all, it was the very first A-bomb and procedures may not have been formalized yet. It occurs to me that maybe a theater commander like Gen. MacArthur could have given the order. Given that Truman was at Potsdam when he made the decision to bomb Hiroshima, did he have a secure method of communications to use to communicate his order from Potsdam? If so, what was that method? When was that order actually given? I'm guessing it was at least several days before the bombing since someone had to order the bomb moved to Tinian and a plane and flight crew chosen and assembled at Tinian. Could Truman have aborted if he'd changed his mind? How late could he have successfully aborted? Right up until the bombardier pressed the "Bombs Away" button? Or would it have been early, say up until the moment Enola Gay left Tinian, after which it might have been running silent? I realize this is all academic now but it's not impossible to imagine Truman having a change of heart and deciding not to bomb Hiroshima. Let's say the Japanese surrendered on August 4 because they could see that the war was lost. I'm curious how late he could abort the bombing if he'd really wanted to.

Answer 1

The moment he was sworn in as president after FDR's death, Truman was notified of the Manhattan Project as well as its progress. The second he knew a bomb was available, he authorized its use. What exactly that chain of command looks like is something that would have to be looked at on a deeper level, simply because the communication involved had to have been highly confidential. Of course most if not all of the communications that occured then regarding the bomb are likely declassified. Truman had no intention of aborting, in fact recent reports show that there have even been a willingness to surrender on the part of the Japanese prior to the bombs being dropped. Some have speculated that Truman used the bombs as a show of American might more directly aimed at the USSR, though of course Japanese civilians suffered the entirety of the bomb's destructive and deadly fallout.