Pearl Harbor thought.

[Admiral Halsey]

Ok I was originally going to put this in my Alternate History thread but I want more responses then I normally get for this post. Ok so here it goes. In this scenario FDR, Kimmel and Short and MacArthur(Plus anyone else who'd need to know) know Japan is going to attack Pearl and the Philippines a few months before the attacks happen. They decided to let Japan hit Pearl BUT they also decide to put all the American Carriers on the Japanese flank and wait for them to blunder into their sights.(So basically Midway at Pearl.) They don't launch the attack on the carriers until the Opana Radar Site sends a signal to them that the planes have been spot on the screen. So basically i'm asking you guys this. Once the American carriers launch their planes into the air what happens next? Oh and yes Pearl will be put on full alert the moment the Japanese planes are confirmed to be heading there.

[Dread Knot]

Admiral Nagumo goes swimming and I think you will likely end up with a super-Midway event. The Japanese are bringing six carriers and veteran pilots true, but in this case Oahu is a far more formidable installation than Midway, capable of basing and dispatching far more aircraft into the air. As always, a lot depends on who gest the first blow in, but foreknowledge is a huge advantage. The only fly in the ointment might be if the US carriers are spotted early by Japanese search planes. Nagumo might elect to retreat at that point.

Even if both carrier fleets end up in a shambles, USN pilots and personnel are far more likely to be rescued by their side than Kido Butai pilots.

[mapuc]

My first impression? The war would end a lot earlier.

Markus

[Dread Knot]

Of course, one political drawback might be no declaration of war by Hitler after seeing his ally in the Pacific getting an embarrassing thumping early on. That puts Roosevelt over a barrel in Congress, trying to get involved in the war in Europe, while one is already raging in the Pacific.

[Admiral Halsey]

Originally Posted by Dread Knot

Of course, one political drawback might be no declaration of war by Hitler after seeing his ally in the Pacific getting an embarrassing thumping early on. That puts Roosevelt over a barrel in Congress, trying to get involved in the war in Europe, while one is already raging in the Pacific.

True but Hitler might be insane enough to still declare war. As for Nagumo retreating he'd have no choice but to fight it out at that point. He'd know that it couldn't be a coincidence that there are American carriers waiting for him on his flank.

[CCIP]

My favourite response to this kind of thing is that real historians hate what-ifs

The real question is just how they would know that much operational detail about the way the Japanese would carry out the Pearl attack. It's one thing to know that the Japanese might attack, another thing to know the exact composition of the task force and attack plan and tactics, and being able to find the ships without the Japanese putting up necessary precautions. And radar during that time didn't really have a great deal of precision, or at least I don't think there was quite that much operational experience in its use. So, that's quite the gamble. I don't think there would be enough confidence in this working.

Something like this would be basically threading the eye of the needle - sure, maybe, but it's one of those things where a whole bunch of things would conveniently have to turn out precisely right for the Americans to pull it off, against an already-wary Japanese task force (they themselves knew they were running big risks, which is why they got out of there fast instead of sending another wave of attacks). Considering this would all be happening while their planes were bombing American soil, I don't think this kind of plan would be approved. Too many things that could go wrong at too high a cost.

[Wolferz]

There was no radar in '41 so no IJN plane could have been spotted except with the MKII eyeball.

[CCIP]

Originally Posted by Wolferz

There was no radar in '41 so no IJN plane could have been spotted except with the MKII eyeball.

That's not true. Opana was opened in 1939, using a 1937-model radar. I would seriously doubt the performance of that radar in any sort of precision, but it did detect the Japanese coming in to bomb Pearl, about 40 minutes before the bombing commenced. They thought it was just a flight of B-17s doing training, then they lost contact, and the warning wasn't passed on. So much for precision.

[Admiral Halsey]

Originally Posted by CCIP

My favourite response to this kind of thing is that real historians hate what-ifs

The real question is just how they would know that much operational detail about the way the Japanese would carry out the Pearl attack. It's one thing to know that the Japanese might attack, another thing to know the exact composition of the task force and attack plan and tactics, and being able to find the ships without the Japanese putting up necessary precautions. And radar during that time didn't really have a great deal of precision, or at least I don't think there was quite that much operational experience in its use. So, that's quite the gamble. I don't think there would be enough confidence in this working.

Something like this would be basically threading the eye of the needle - sure, maybe, but it's one of those things where a whole bunch of things would conveniently have to turn out precisely right for the Americans to pull it off, against an already-wary Japanese task force (they themselves knew they were running big risks, which is why they got out of there fast instead of sending another wave of attacks). Considering this would all be happening while their planes were bombing American soil, I don't think this kind of plan would be approved. Too many things that could go wrong at too high a cost.

But at the same time the rewards would be extraordinary. Think about how different the Pacific war would go if in one swoop not only is Pearl saved(Remember the moment the radar station confirms it's the Japanese coming in Peal goes to full alert) or not heavily damaged and the majority of Japan's carriers are wiped out. Also Midway was a threading the needle type situation and it worked perfectly then and is this case you'd have nearly the same scenario.

[CCIP]

Of course. But again, I think the only way this would actually fly is if somehow the fog of war disappeared completely. I just don't see how Americans would have access to that level of detail about Yamamoto's attack plans - it would be an extraordinary achievement of intelligence. You'd probably have to have an IJN rear admiral working as a spy for the Americans to really make it work.

[Admiral Halsey]

Originally Posted by CCIP

Of course. But again, I think the only way this would actually fly is if somehow the fog of war disappeared completely. I just don't see how Americans would have access to that level of detail about Yamamoto's attack plans - it would be an extraordinary achievement of intelligence. You'd probably have to have an IJN rear admiral working as a spy for the Americans to really make it work.

Or they just need to put together the information they had in RL.

[Oberon]

They knew the IJN was heading towards Pearl, they didn't know where it would be launching from. The US Armed Forces would need to be much more co-ordinated than it was at the time for the information to reach the right places at the right time. If the radar at Pearl had picked up the Japanese airforce coming in, it would still probably have taken a couple of hours to relay that information to the US carrier force steaming in circles around Hawaii. Then that would have taken another couple of hours to head into position, Nagumo would have had spotter planes circling the fleet and the first indication that the US was ready for them he would have run like hell back to Japan. Likewise if the first wave had met with overwhelming defences, the second would likely have been recalled and the attack aborted.

Honestly though, it requires a lot of things to go right for the Americans and for them to actually be organised, something that the American command system really was not in 1941.

[CCIP]

Again, that's only a success assuming reliable radar information they could actually trust, the Japanese behaving exactly as expected, scout planes finding the Japanese fleet at exactly the right time AND not provoking an immediate defensive reaction from them, and everything else working perfectly. But I'd give it something like a 1% chance of actually succeeding.

In that sense, I think disrupting their attack plan, moving the fleet, sending submarines to try and pick off the carriers would probably be a much better way of giving the Japanese war plans a headache. The Americans didn't really need such a total success to make life more difficult just for the enemy - being able to constrain their total freedom of movement in the first few months of the war (even by making them waste resources keeping their main fleet constantly ready for that Mahanian decisive line battle) would be more than enough.

[Admiral Halsey]

Ok after thinking it over i'll add a wrinkle to this. It mainly concerns HOW the US is able to discover the plans. Basically sometime in 1940 JN25 is broken. Japan thinking that the code can never be broken doesn't change it in anyway until AFTER the Attack on Pearl.

[TorpX]

I think the kind of knock-out blow that occurred at Midway would be unlikely. Possible, but not likely. The IJ air groups had a better state of training/skill/operational readiness. An ideally coordinated ambush is hard to pull off. There is a lot or room for 'operational chance' here.

More likely, the Japanese would have lost a lot more aircraft over Pearl, and we would have lost a lot fewer ships. You didn't say if the USN battlewagons would be left at anchor, as bait, or at sea, ready to pursue the enemy fleet. If our carriers attacked at the wrong moment, it could be a disaster, anyway.

I think the most interesting question is what would the Japanese do? When they realized they were being stalked, they would presumably head for safe harbors, but then what? Would they continue with their invasion of the P.I. and D.E.I., without having the advantage they were counting on, or meekly accept a difficult peace without fighting?