My understanding is that there were enough planes at Hickham Field to give the Japanese attackers at least a good fight if they had heeded the Radar warning they got and had them in the air waiting.
Absolutely. And even more so if Kimmel had gotten the aircraft he requested. The book to read on this, and on the entire run up to Pearl is "Day of Deceit" by Stinnett. It is an extremely worthwhile book.
What if the attack had failed, and spectacularly because the American planes followed the attackers back and then more planes and ships from Pearl attacked the Task Force.
Which is totally plausible. As far as the U.S. aircraft go that is. The ships not so much. I don't think we had anything there fast enough unless the Japs waited for us to hit back like a bunch of suckers. But had the horseshoe nails dropped differently, it could easily have happened that way.
The declining importance of the battleship AT THAT TIME has been greatly exaggerated. They didn't form Napoleonic lines of battle and duke it out in massive fleet actions as at Jutland, but that change was already understood. It is true that their vulnerability to aircraft had been underestimated, but the vulnerability of carriers to surface ships had also been underestimated and both mistakes were soon corrected and tactical doctrine adapted. Battleships were far from obsolete. They were a huge factor in amphib ops. And the Pacific war was all about island hopping. Even in the 1990s when the last battleships were retired, the protests came mainly not from the regular Navy per se, but from the Marines. There was a significant body of opinion that even then they weren't obsolete and that in terms of support of amphibious operations the navy did not have anything quite as effective.
So, yes, OF COURSE, the immediate loss of all U.S. battleships in the Pacific, and half of all U.S. battleships anywhere made a big difference. It took a month to get 2 of the 8 back in service and a year or so for another 4. In war, that's a long time. And 2 were total losses. Furthermore, for the attack to have been a tactical failure implies the U.S. wouldn't have lost half the aircraft based there and that the Nips would have lost a lot of the attacking aircraft. That might indeed have put their carriers at risk if a counterattack was swift. And of course, with a little more accurate anticipation, a counterattack would have already been planned. Stuff like that snowballs. Very possibly the Japanese would have never taken the Philippines and if they did they certainly wouldn't have held them as long. Probably they'd have been pushed back to the home islands long before the bomb was developed.
That is where it gets interesting. With a quicker victory in the Pacific, Wild Bill Donovan (may he RIH and that's no typo) might have never backed Mao. More resources would have become available to the European theater faster. The Warsaw Pact would have wound up much smaller. The world might be very different indeed in that case. More likely better than worse, but you never know, chaos always rules.
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Now about the stuff later posters wandered away from OP's question into:
Whether Truman was right to drop the bomb is a darned complex topic. I used to think obviously yes, for many of the reasons advanced here. Later I learned more and switched my view to no. Then I learned still more and realized it is darned hard to say.
- The Nips DID offer surrender well before the bomb was dropped. I'd have to look it up but I believe it was a few MONTHS before. Certainly more than a couple of weeks. The terms they asked for were NOT materially different from those Mac unilaterally granted as the occupying American shogun. If you want to look at it in terms of the effect on Japan, then the difference was NOT in terms of actual conditions but the different psychology of:
-- your face has been unambiguously, undeniably ground in the dirt, indeed you have no more "face" at all, your total impotence has been demonstrated, and you have rolled on your back like a whipped dog begging for mercy, knowing Halsey can and will make good his threat ("the Japanese language will be spoken only in Hell") if allowed, and the conqueror has graciously unilaterally ALLOWED you the concessions you wanted to get by negotiation, after demonstrating he can easily cause the total extinction of your culture, the near extinction of your race, and literally sterilize the home islands . . .
vs.
-- being allowed to save face by negotiating a peace, possibly allowing future Japanese politicians to capitalize on claims like Hitler's "stab in the back" claims vis a vis Versailles.
The trad leftist anti-war view (not counting those who just ignore the facts as inconvenient), moderated only by their loyalty to Truman's party, is that that was just pure evil on Truman's part since their was no MATERIAL difference and the war ran on months LONGER than it needed to, costing MORE lives, not less.
But realistically, you can't ignore the psychological effect. Japanese culture and politics is profoundly different than it would have been. On that score, he may have been right.
And yes, of course the bombing was a cautionary message to the Soviets. He might have been right on that score too. Damfino.
But there is another joker in history's deck almost never acknowledged, partially, I suspect, for reasons that draw on unconscious racism or cultural chauvinism, and the comforting, unstated, and false belief that westerners innovate and asians imitate. While the Germans largely kept their wartime records, the Nips engaged in massive destruction of records beginning months before the end. And, bizarrely, a huge portion of those documents that WERE captured, after being held in the U.S. for a few years, during which the majority were never scrutinized (or so it is claimed - Finagle knows what the truth is), were then returned to Japan. This may or may not have bearing on the credibility of some of what follows. Furthermore, as recently as the Clinton administration (see the excellent Pearl Harbor book "Day of Deceit" mentioned above) the U.S. still had classified documents from BEFORE Pearl Harbor that they refused to declassify. I presume they still do. Furthermore I'd presume that the refusal to do so is NOT driven by any military consideration, but a desire to spin history. Hard to say. There is a bio of Hirohito, which is worth reading. I THINK the title was simply "Hirohito", but I may misremember. I believe the dust jacket was largely white with a photo of Hirohito mounted on a horse, although it is possible I am confusing 2 different bios of the man. I remember nothing about the author, but it struck me as credible when I read it. Most of the following comes from that. There was a German submarine ordered to carry a cargo to Japan late in the war. It was in the mid Atlantic when the order came to proceed to the nearest Allied port and surrender. The Captain figured his proximity to England and New York city essentially the same and actually polled the crew to see if anyone had a preference. Not surprisingly, there was a strong preference for New York and that's where they went. Two Nips aboard promptly committed sepuku or whatever they call it, and were polite enough to use poison, rather than make a mess. The cargo being delivered was uranium. I believe it was already isotopically enriched, but I may be mistaken on that point. Meanwhile, back in the far East, there was at least one witness (I want to say a German, but I'm hazy on that point) who claimed to have seen a test fission bomb detonated by the Nipponese army on the mainland in what would now, I believe, be North Korea. It was suggested that the plan was to use the bomb on the expected invasion fleet.
Even if you assume this is true (and provisionally, I'd bet even money it is), it still seems likely that Truman didn't know it at the time the decision was made to drop the bomb on Hiroshima. However, it also seems likely that unless Truman was a lot stupider I think he was, he was probably aware that there was at least a CHANCE that something like this might be the case. This is true even if the factoid, as Mailer would say, of Japan's fission bomb program is false. And even if he evaluated that chance as very low, it is still something he would have to take into account. He also couldn't exclude the possibility that they didn't have it, but were 6 months FROM having it, for example. Imagine yourself in his position. Does that idea push you toward taking the peace offer and shortening the war, or toward the idea of waiting a little bit longer in order to damage Japanese industry in a really big way, and, bluntly, totally cow the leadership, before occupying it? The more you think about it, the more layers of complexity you see.