Today is the 68th anniversary of the atomic bombing of Nagasaki. Everyone knows that Nagasaki came three days after Hiroshima — but Nagasaki doesn't get talked about nearly as much. The reason Nagasaki gets "overlooked" is pretty obvious: being the second atomic bombing attack is a lot less momentous than the first, even if the total number of such attacks has so far been two.
A temple destroyed by the bombing of Nagasaki. Original source. Slightly edited to improve foreground/background distinction.
We all know, or think we know, why Hiroshima was bombed. This is because the bombing of Hiroshima is synonymous with the use of the atomic bomb in general. But why was Nagasaki bombed?
I don't mean, why the city of Nagasaki as opposed to another city. That is well-known. Nagasaki only made it on the list after Kyoto was removed for being too much of an important cultural center. The initial target on August 9 was Kokura, but there was too much cloud cover for visual targeting, so the Bockscar moved on to the backup target, nearby Nagasaki, instead. Bad luck for Nagasaki, twice compounded.
What I mean is: Why was a second atomic bomb used at all, and so soon after the first one? Why wasn't there more of a wait, to see what the Japanese response was? Was less than three days enough time for the Japanese to assess what had happened to Hiroshima and to have the meetings necessary to decide whether they were going to change their position on unconditional surrender? What was the intent?
There are, unsurprisingly, a number of theories about this amongst historians. There are some that think Nagasaki was justified and necessary. There are also many who agree with the historian Barton Bernstein, who argued that: "Whatever one thinks about the necessity of the first A-bomb, the second — dropped on Nagasaki on August 9 — was almost certainly unnecessary." And there are those, like Tsuyoshi Hasegawa, who don't think either of the atomic bombings had much effect on the final Japanese decision to unconditionally surrender when they did. (I will be writing a much longer post on the Hasegawa thesis in the near future — it deserves its own, separate assessment.)
The following images are screens taken from footage taken of the Fat Man preparations on Tinian, courtesy of Los Alamos National Laboratory. Above, preparing the final weapon, sealing the ballistic case joints with red Pliobond and blue Glyptol (plastic film). The different colors made it clear that they were properly applied and overlapped.
The first is the standard, "official" version — the second bomb was necessary to prove that the United States could manufacture atomic weapons in quantity. That is, the first atomic bomb proved it could be done, the second proved it wasn't just a one-time thing. One wonders, of course, why anyone would think the Japanese would think the atomic bomb was a one-off thing, or that the Americans wouldn't have the resolve to use it again. They had, after all, shown no flinching from mass destruction so far — they had firebombed 67 Japanese cities already — and while making an atomic bomb was indeed a big effort, the notion that they would be able to make one and no more seems somewhat far-fetched. The idea that the US would have a slow production line isn't far-fetched, of course.
What did the participants in the decision to bomb have to say about the use of specifically two bombs? General Groves told an interviewer in 1967 that:
...it was not until December of 1944 that I came to the opinion that two bombs would end the war. Before that we had always considered more as being more likely. Then I was convinced in a series a discussions I had with Admiral Purnell.
Which, if true, would peg this decision fairly early in the process. In his memoirs, Groves also has this little exchange from just after the "Trinity" test:
Shortly after the explosion, [Brig. General Thomas] Farrell and Oppenheimer returned by jeep to the base camp, with a number of others who had been at the dugout. When Farrell came up to me, his first words were, "The war is over." My reply was, "Yes, after we drop two bombs on Japan."
Both of these, of course, are recollections made long after the fact. And Groves is known to have "smoothed" his memories in order to present him in the best possible light to posterity. The actual instructions for the use of the bomb, from late July 1945, only give detailed information about the first bomb:
1. The 509 Composite Group, 20th Air Force will deliver its first special bomb as soon as weather will permit visual bombing after about 3 August 1945 on one of the targets: Hiroshima, Kokura, Niigata and Nagasaki. [...]
2. Additional bombs will be delivered on the above targets as soon as made ready by the project staff. Further instructions will be issued concerning targets other than those listed above.
President Truman, in his diary entry, referred to the impending use of the atomic bomb as a singular thing. In his public statements after Hiroshima (which he probably did not write), he claimed that many more atomic bombs would be used until the Japanese surrendered. That being said, he did put a "stop" on any further bombing on August 10th, to wait for a response. This didn't have any immediate consequences on Tinian, since the next, third bomb wouldn't have been ready for a few more weeks, and even then, it wasn't clear whether it would have been immediately dropped or "saved" for a multi-bomb raid.
The bomb prepared, it was then sheathed in canvas and towed out to the loading bay. I find the shot on the right particularly ominous — the second bomb, still a secret, its size and probable importance not quite masked by its shroud.
Oppenheimer, for his part, seems to have expected that both "Little Boy" and "Fat Man" units would be used in combat. In a memo sent on July 23, 1945, Oppenheimer explicitly discussed the expected performance of "the first Little Boy and the first plutonium Fat Man." Notably, he expressed near complete confidence in the untested Little Boy:
The possibilities of a less than optimal performance of the Little Boy are quite small and should be ignored. The possibility that the first combat plutonium Fat Man will give a less than optimal performance is about twelve percent. There is about a six percent chance that the energy release will be under five thousand tons, and about a two percent chance that it will be under one thousand tons. It should not be much less than one thousand tons unless there is an actual malfunctioning of some of the components.
Which raises the interesting secondary question of why Little Boy went first and Fat Man went second. Was it because Little Boy was the more predictable of the two? There's very little about this that I've seen in the archives — it seems like it was taken for granted that the gun-type would be the first one. Groves claimed later that the order was just an issue of when things ended up ready to be used on the island, but the components for both were available on Tinian by August 2, 1945, in any event.
Oppenheimer had, interestingly, earlier suggested to Groves that perhaps they ought to disassemble the 64 kg enriched-uranium core of Little Boy and use it to create a half-dozen enriched-uranium Fat Man bombs. Groves rejected this:
Factors beyond our control prevent us from considering any decision other than to proceed according to existing schedules for the time being. It is necessary to drop the first Little Boy and the first Fat Man and probably a second one in accordance with our original plan. It may be that as many as three of the latter in their best present condition may have to be dropped to conform with the planned strategic operations.
All of which is to say that the Los Alamos people seemed to assume without question that at least two bombs would be necessary and would be used. At the higher levels, while Truman did publicly proclaim that further atomic bombings were follow, it isn't terribly clear he was clued in on the actual schedule of those which followed the first. I wonder if his order to stop bombing, issued immediately after Nagasaki (and the Soviet declaration of war on Japan) wasn't partially a reaction to the fact that he suddenly felt out of control of the military situation over there.
On the left, the bomb being unshrouded, just before loading into the B-29, Bockscar. On the right, the results: the fireball and mushroom cloud, seen through the window of one of the B-29s on the Nagasaki raid, just a few seconds after detonation, roiling and rapidly rising.
The historian Stanley Goldberg proposed another theory: that two bombs were necessary in order to justify the decision to pursue both the uranium and plutonium routes. That is, Little Boy would justify the (enormous) expense of Oak Ridge, and Fat Man would justify Hanford. To support this argument, Goldberg points out that during the war Groves was completely afraid of being audited by Congress in the postwar. Groves knew he was engaged in a huge gamble, and he also knew he had made a lot of enemies in the process. This is one of the reasons that he meticulously documented nearly every decision made during the Manhattan Project — he wanted "evidence" in case he spent the rest of his years being subpoenaed. It's a clever argument, though it relies heavily on supposition.
Michael Gordin has argued that this entire question revolves around a false notion: that it was known ahead of time that two and only two bombs were to be used. That is, instead of asking, why were two, and not one, used, Gordin instead looks into why were two, and not three, four, and etc. used. Gordin's book, Five Days in August, argues that it was assumed by Groves and the other planners (but not necessarily Truman) that many more than two bombs were going to be necessary to compel Japan to surrender — that the surprising thing is not that the bombing cycle continued on August 9, but that Truman stopped the bombing cycle on August 10.
Of these options, I tend to lead towards Gordin's interpretation. The decision-making process regarding the atomic bomb, once the Army took over the production side of things, was that they would be used. That is, not that it would be used, though the importance of the first one, and all of the import that was meant to be attached to it, was certainly appreciated by the people who were planning it. But it was never intended to be a one-off, once-used, anomalous event. It was meant to be the first of many, as the atomic bomb became yet another weapon in the US arsenal to use against Japan. The use of the bomb, and continued bombings after it, was taken by Groves et al. to be the "natural" case. To stop the atomic bombing would have been the unusual position. Go back to that original target order: the only distinction is between the "first special bomb" and the "additional bombs," not a singular second special bomb.
So "Why did they bomb Nagasaki?" might not be the right question at all. The real question to ask might be: "Why did they stop with Nagasaki?" Which, in a somewhat twisted way, is actually a more hopeful question. It is not a question about why we chose to bomb again, but a question about why we chose not to.