According to Rhodes, quoting the Secretary of Commerce:
"Truman said he had given orders to stop the atomic bombing. He said the thought of wiping out another 100,000 people was too horrible. He didn't like the idea of killing, as he said, "all those kids"."
Presumably you are quoting the 1986 book published by Simon & Schuster by the novelist and journalist Richard Rhodes. Well, without context, I don't know if Mr. Rhodes was being deliberately misleading or not. I'm pretty sure this comes from Henry Wallace's diary entry on the cabinet meeting of 10 August. AFAIK, there is no transcript of the meeting. Also, AFAIK, Wallace is the only one present at the meeting who ever made this claim. There were lots of other diarists in the military and in the administration and AFAIK none of them ever claimed the prez gave such an order.
What Wallace wrote CHARACTERIZES what he alleged HST said but for the most part does not quote it. The only words he actually quotes were "all those kids". The problematic sentence:
"Truman said he had given orders to stop atomic bombing."
Wallace may have INTERPRETED whatever HST said that way, but there is no evidence that I know of that anyone in the chain of command had received any order remotely like that other than the one I've already mentioned - that the next bombing mission was to get explicit last minute authorization from POTUS, before taking off, nor AFAIK has anyone in a position to know of such an order made such a claim. The added requirement for last minute POTUS clearance in no way affected the preparations. Nor did anyone else ever claim that HST gave any indication that he had pre-decided NOT to ok the third bomb if it came down to it.
In contrast there is plenty of evidence from people who WERE in the loop that preparations for additional bombing continued up until it was clear that the surrender was real and that the people doing the surrendering were in control. Examples:
Here you can read a transcript of a conversation between General Hull and Colonel Seeman of Grove's staff, partly in modern type in html and more completely in a pdf containing photographs of the original typewritten transcript dated 13 August 1945:
The Third Shot and Beyond (1945)
If HST had already "vetoed" a 3rd bomb, obviously these people would have known about it. Clearly their discussion does not even consider the possibility of NOT dropping more bombs absent unconditional surrender. They are instead, discussing times of availability and possible uses, particularly the possibility of shifting from more strategic targets to possible tactical targets in support of an invasion.
Here is a memo from Groves to Marshall on 10 Aug 45 indicating plans to drop a bomb during "the first suitable weather after 17 or 18 August":
http://www.gwu.edu/~nsarchiv/NSAEBB/NSAEBB162/67.pdf
At the time of the surrender, the next bomb was in already in transit to where it would fly from. Paul Tibbets in a 2002 interview said:
"See, the first bomb went off and they didn't hear anything out of the Japanese for two or three days. The second bomb was dropped and again they were silent for another couple of days. Then I got a phone call from General Curtis LeMay [chief of staff of the strategic air forces in the Pacific]. He said, "You got another one of those damn things?" I said, "Yessir." He said, "Where is it?" I said, "Over in Utah." He said, "Get it out here. You and your crew are going to fly it." I said, "Yessir." I sent word back and the crew loaded it on an airplane and we headed back to bring it right on out to Trinian and when they got it to California debarkation point, the war was over."
- from an interview published in The Guardian (a Brit newspaper), full text archived here:
Nuclear special: Why the pilot of the Enola Gay has no regrets
If you prefer secondary sources this is from "Five Days in August:
How World War II Became a Nuclear War" by Michael D. Gordin who is the Rosengarten Professor of Modern and Contemporary History at Princeton University published by Princeton University Press in 2007:
"Almost nobody before 14 August thought that two bombs would be sufficient: if the first bomb did not cause surrender, the American decision makers reasoned, then many would be required, at the very least a third bomb before the end of August, and likely several others before the scheduled invasion. . . .Discussion of target and timing for the Third Shot—most likely Tokyo on 19 August— proceeded actively both before and after Nagasaki. Such preparations continued even between surrender and the beginning of the American Occupation of Japan on 2 September, a transitional period when Allied forces feared that a militarist coup might restart hostilities. The Third Shot was a reality in progress until unconditional surrender—seen as the two bombs’ success—began the rapid and mostly unconscious process of expunging it from historical memory."
Against this kind of information we have the single diary entry of one slightly kooky (he dabbled in spiritualism for example) Secretary of Commerce who had never been in the military, whose expertise lay in farming, and who was in no way involved in war planning, paraphrasing, but not quoting, what he claimed Truman SAID he had done. Maybe he did say it. It's possible. HST was not a totally honest man. He often gave conflicting accounts of his own actions. See "Harry S. Truman: Advancing the Revolution" by Ralph Raico in "Reassessing the Presidency: The Rise of the Executive State and the Decline of Freedom" edited by John Denson, which BTW is one of the most persuasive essays arguing the bombing-Hiroshima-was-evil position I've seen. I have great respect for both Raico and Denson. They might even bring me around to their point of view.
But regardless of what was SAID, continuing to build bombs as fast as possible and preparing to drop them was what was DONE.
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