Years later, on a business trip to Kyoto, I had a meeting with one of Japan's preeiminent material scientists. He treated me to lunch, (nagi) and during lunch, he revealed that, as a young army officer, he had been one of the first persons who went into Hiroshima after the bombing.
After I explained that, at the time, I was an "aka-chan", and my only recollection of the time was a hazy memory of adult comments about some sort of "secret weapon" being used, he said this:
"That was an awesome weapon. If Nippon had had it, Tojo Hideki undoubtedly would have used it on Los angeles and San Francisco. As you can see, I survived my trip into the devastation. Conversely, I almost certainly would not have survived the forthcoming U.S. invasion. You might say that the A-bombs made it possible for us to enjoy this lunch together."
You can't get a much more personal observation and knowledgable opinion than that!
Sagamihara & Yokohama, 1951-1961. Army brat.