The focus on the horror of atomic bombs should not distract from the horrors of “conventional” warfare; the firebombings of cities in WWII are to my mind on the same level as the atomic bombings in their inhumanity. They lack only the long-term radiation-induced health consequences. Even using conventional means only – in some parallel world in which we did not develop the atomic bomb – the probable death toll in Japan from aerial bombings would have been truly beyond description. Add to that the loss of life in the invasion which would follow, and it becomes truly staggering.

If one is concerned with ending the war while minimizing the total loss of human life, then avoiding an invasion of the Japanese home islands becomes a priority. The choice then becomes a conditional surrender or using the atomic bombs. There may have been other choices with the potential for less human cost, but they were not without their own risks in the long term. The merits of the various approaches can be debated without resolution interminably. I’m just glad we got out of it as cheaply as we did and with Japan as an ally for the last sixty-plus years and the foreseeable future.

Tinian had at least one spare bomb housing on hand, another Fat Boy design missing only its plutonium core. It is possible that another weapon in addition to this third one could have been used on Japan by the end of August.

The really scary thing was that the Boeing plant in Seattle was producing 300 B-29 bombers a month and large numbers of B-17 pilots from the European war theatre were ramping up conversion training. By the time the Olympic/Coronet invasion took place in late October Japanese cities could have been subjected to massive “conventional” bomber raids every day and night until there was nothing left worth bombing on the Home Islands.

As to the assertion regarding the state of knowledge of the Japanese nuclear scientists, I can only trust my source, which ultimately is a recently published book: “The Nuclear Express: A Political History of the Bomb and Its Proliferation”, by Thomas C. Reed and Danny B. Stillman. (Curiously, I heard about book in a review of the stage play “Dr. Atomic” in the New Yorker.) Stillman and Reed both had long careers in the nuclear weapons field in the Cold War, so they should know what they’re talking about.

They assert that Japan had two atomic-bomb programs during the war. One was Project N, at the Aviation Technology Research Institute, in Tokyo, overseen by Yoshio Nishina. Its work was largely destroyed by firebombing early in 1945; they lost their small cyclotron though the larger 60-inch cyclotron survived. The second project, the F-Go project, operated by the Navy, was situated at the Imperial University of Kyoto and involved centrifuge research; its facilities survived the war, but the researchers made only a little technical progress. However, according to the book, Nishina and the chief of the Kyoto project, Bunsaku Arakatsu, knew enough about nuclear weapons at the time of the Hiroshima bombing to be able to advise the Japanese government about the nature of the bomb used by the Americans, its yield, and its fissile material—uranium, in the case of the Hiroshima bomb. Information about these two projects can be found in the book “Yoshio Nishina: Father of Modern Physics in Japan”, by Dong-Won Kim.

After Hiroshima, the Japanese scientists concluded, correctly, that the United States must have labored long and hard to create enough U-235, the difficult-to-extract fissionable isotope of uranium used in atomic bombs, and that they probably did not have any left—the Hiroshima bomb was a one-time shot, at least for now. After Nagasaki, however, these scientists recognized the plutonium used in that bomb and understood that it must have come from a working reactor—and, therefore, there would be more where that bomb came from. The authors surmise the scientists’ advice to the Japanese war cabinet after Nagasaki: “Better take this one seriously; better accede to American demands; there are probably more plutonium bombs.”

While it’s been nearly 30 years since I earned my (unused) degree in nuclear engineering, I retain enough to speculate that if one knew what to look for, it shouldn’t be that hard to distinguish between the fallout from a uranium bomb and a plutonium bomb.

One the other hand, the irony is that the Americans really didn’t have any more bombs, of either kind, and they wouldn’t for months. While it’s difficult to find precise information, it seems that at the time of the Bikini Atoll tests the next summer (July 1946) there were only ten bombs: “…the two tests used twenty percent of the available inventory.” That implies a production rate of around one per month, which sound reasonable. One can hazard a guess that if the Japanese had refused to surrender after Nagasaki, the next bombing would not have happened for at least a month and probably longer.

Fortunately, two was enough. The tragedy of course is that any had to be used at all.

That said, I’ve always been ultimately comfortable with the decision to use it, even as early as the 9th. It’s not clear to me that the Imperial Army was ready to quit or that an order from the Emperor wouldn’t have been creatively interpreted in such a way as to really ignore it. While Hirohito, of course, had huge influence on Japan, he still let his government (i.e., the junta) run the show.

All great questions to ask, however, and I look forward to reading this one. What atomic bomb history books did you rely on in getting up to speed on the subject of Manhattan and the like? I’ve read most of the big ones and will be curious to see how your research plays out.

First, how essential was it to define the “unconditional surrender” of Japan in the most draconian terms imaginable? From the enemy perspective, the Potsdam Proclamation clearly allowed for Emperor Hirohito to be tried and executed as a war criminal, an intolerable thought for the Japanese — and surely one reason for Tokyo’s maddeningly equivocal reaction to the ultimatum. And yet, ironically, after Hirohito finally demanded that his generals capitulate, there was evidently no sentinent among the Allies for arresting him. Indeed, McArthur allowed the Emperor to remain the titular head of his nation, a gesture that proved essential for shutting down the tattered but fanatical remnants of Japan’s once mighty military machine.

Third, how necessary was it, both to immediate American interests and to the welfare of humankind in general, that the Pacific War end with minimal assistance from Stalin? It’s worth remembering that, the day before the Nagasaki attack, the Soviet Government officially declared war on Japan. Some historians have concluded that, even without the atomic-bomb factor, the Japanese would have ultimately surrendered in consequence of massive Soviet involvement — a situation that Truman, of course, could not countenance, given his understandable desire to curtail Stalin’s postwar influence in the Far East.

I only ask. I do not know.

When the Japanese cabinet was discussing the allied demand for surrender on August 9, they had two pieces of news. One was that a second city had been destroyed, the other was that the Russians had declared war (on the date long agreed, 3 months after the end of hostilities in Europe). Both must have had an impact, but there were still some calling to continue fighting even in the face of further destruction of cities.

While the Japanese nuclear program, such as it was, was nowhere near advanced enough to produce a bomb, their scientists were knowledgable enough about the technical issues involved to tell the military that the Hiroshima bomb was a Uranium bomb, and that such bombs required difficult and expensive separation of U235 from U238. They speculated that the Americans probably didn’t have any more of them.

After Nagasaki, the scientists told the military “That was a plutonium bomb. All you need for those is a reactor. They probably have more.”

Just a technical detail often overlooked in the emotional discussion of one of the great tragedies of the last century.