Plausibility Check: An Earlier Pearl Harbor

What would be earliest month in 1941 that the Japanese could have carried out the attack on Pearl Harbor before the December 7th attack of OTL?
 

CalBear

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November 1941. Shokaku & especially Zuikaku were not ready until then. Shokaku finished her shakedown cruise on August 25, 1941. Zuikaku completed her abbreviated shakedown cruise on November 5, 1941.

The attack plan required six decks. The Japanese made the attack virtually the first Sunday (which had been determined to be the day most likely to find the fleet in port, gotta love the peacetime Fleet) they had the forces available to make it. As was Zuikaku's attack aircraft were assigned to only land targets because, in the opinion of the IJN command, they were not yet experienced enough to handle attacking warships.
 
If some ass-brained reason Japan decided to go with only 4 carriers, then any time in 1941. Otherwise you have to modify the build/ready time of the Shokaku and Zuikaku. Or they decide to use the smaller carriers.
 
If some ass-brained reason Japan decided to go with only 4 carriers, then any time in 1941. Otherwise you have to modify the build/ready time of the Shokaku and Zuikaku. Or they decide to use the smaller carriers.

The earliest would be October, because the modified torpedoes required by Pearl Harbor's shallow depth were not available earlier.
 
An earlier attack was unfeasible, the Japanese and U.S were still in negotiations about a modus vivendi on the U.S embargo and asset freeze from June until late November.
 
Actually as much as Carrier availability is a factor in planning the attack. You have to remember the attack on Pearl Harbor is not an end unto itself. It is a diversion/flank protection for the primary operation, the attack on the Southern Resource Area. When was the shipping and air support available for that attack? That is your earliest possible date. Then, if a Pearl Harbor attack is decided on to support the main attack, then carrier availability becomes a factor in determining the date.

But everything is first determined by the attack on the oil fields, that is the entire purpose of the war...
 
Actually as much as Carrier availability is a factor in planning the attack. You have to remember the attack on Pearl Harbor is not an end unto itself. It is a diversion/flank protection for the primary operation, the attack on the Southern Resource Area. When was the shipping and air support available for that attack? That is your earliest possible date. Then, if a Pearl Harbor attack is decided on to support the main attack, then carrier availability becomes a factor in determining the date.

But everything is first determined by the attack on the oil fields, that is the entire purpose of the war...
Except that the OP specifically asks about Pearl.

An attack on the Philippines and DEI could have been done earlier, no doubt. But once they decided that 'a punch to the nose' would get the US to back down/stay out, they pretty much had to do Pearl, and that meant waiting until Dec 7. (Or maybe Nov 30 or so)
 
Except that the OP specifically asks about Pearl.

An attack on the Philippines and DEI could have been done earlier, no doubt. But once they decided that 'a punch to the nose' would get the US to back down/stay out, they pretty much had to do Pearl, and that meant waiting until Dec 7. (Or maybe Nov 30 or so)

In that case you are indeed correct. Operation AI has to have 6 Carriers which puts it at late November, at the earliest, depending on the exact date Zuikaku can sail. And the first Sunday after that date that the attack force can be in position.
 
PH had to go more or less simultaneously with the attacks in the PI and elsewhere. If you attack anywhere except PH first, then the whole concept of catching the fleet in port, not alert, etc. If you don't "eliminate" the US fleet then even the Japanese knew they were screwed - some parts of the IJN thought missing the carriers was not important, Yamamoto felt otherwise which is why Midway, he knew he needed to take out the US carriers to truly emasculate the fleet. OTOH if you give the PI too much time to wake up after PH, you have a much harder time. OTL because of the weather delay the Japanese attack on the PI was delayed however MacArthur, for whatever reason, as well as subordinates did not take advantage of this gift. Basically, like all Japanese plans, the plan for the operations at the beginning of the Pacific War had lots of moving pieces all linked together. You had to have enough decks and pilots for the PH campaign, get the transports and escorts for the PI, SEA attacks together, and so forth. Even so some attacks, like Wake Island were very shoestring. Given the limits of Japanese non-naval shipping gathering transports, oilers, etc together took time and planning and meant pulling ships off "normal" activities.

All of this means that putting aside 4 vs 6 carriers, and assuming you can get the shallow water torpedoes sooner, to getan attack much sooner you need to have the government come to the decision for war much sooner.
 

raharris1973

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OK- Say if Japan's hand is forced by an earlier embargo, starting in March 1941 [maybe the Japanese provoke it by moving from northern to southern Indochina faster than OTL, maybe US policy is just more economically aggressive].

This puts Japan on a clock to require takeover of the Dutch East Indies several months earlier, yet, they don't have a sufficient strike force to do Pearl.

Do the Japanese:

a) Give in to US political demands and withdraw from occupied China because they cannot disable the US fleet in a surprise stroke

b) revert to their pre-Pearl plan of just striking south (including the Philippines) and accepting that any fleet from the US would not be crippled in 1 blow but would have to be attrited and ambushed as it advanced to the western Pacific
 
I think that unless someone wants to offer more why Japan would go for an earlier attack and the background for it, it may be it.
 

GarethC

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Maybe the OP could turn it around - give us the date you want the attack to go in on, and the varied wise heads here will probably be able to come up with estimates for the orders of battle of both sides, what the effect of reduced training will be. that sort of thing.
 
Do the Japanese:

a) Give in to US political demands and withdraw from occupied China because they cannot disable the US fleet in a surprise stroke
Ha, ha. And get promptly assassinated. Nope. Not going to happen.

b) revert to their pre-Pearl plan of just striking south (including the Philippines) and accepting that any fleet from the US would not be crippled in 1 blow but would have to be attrited and ambushed as it advanced to the western Pacific

My guess is that they might convince themselves that the Philippines wasn't 'real' US territory (after all the US Constitution didn't apply there), so Japan could conquer it and offer the US some sort of compensation later.

Not that that would work, but nothing Japan can do in WWII would work.
 

raharris1973

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So I read that as an endorsement of b) - a strike to the south that includes attacks on US possessions but not Hawaii, and that anticipates US intervention.

The idea for Japan that it was "strike Pearl Harbor or bust" was a late addition that Yamamoto insisted on. If unavailable, the Japanese would go for b) the scenario they had been planning for for years. And yes they'd still lose the war, but depending on the particular circumstances at the time of their attack they may match OTL's initial success on Southeast Asia and the Western Pacific
 
If Japan does not take PH the US fleet, as well as Army/Navy/Marine air in Hawaii is untouched. Such damage as was done to fixed facilities is not done. The panic and a need to rebuild Hawaii's defenses not there. Wake Island probably does not fall as it can be reinforced pretty easily. Places like Samoa get reinforced quickly and more forces go to Australia and you may even see some of the Southern PI being held. The day of the battle line is over, but having those ships, as well as others that were sunk/damaged at PH helps the USA and hurts Japan.

The whole Japanese plan was to knock the USA back on its heels and render the military impotent long enough to create the defensive barrier as well as grab the resources. At that point they expected the USA not to be willing to expend blood and treasure but give up. BTW IMHO a sneak attack on the PI and Guam will piss off the USA just as much as PH. Finally, Japanese strategic/military thinking was based on striking the first decisive blow. Not hitting the US fleet violates this.
 

raharris1973

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yet, the non-Pearl Harbor plan was the default plan for nearly 20 years.

Remember, some dispute whether Pearl was even conceivable before Taranto.

Do you think the Japanese had no plans against the US until Yamamoto proposed the Pearl plan in 1940 or 1941?

Also Sloreck, is the implication you're giving that the Japanese would cave in to all US political demands in Asia before if they have no plan that satisfies the need to strike the US fleet first? I think they'd implement an imperfect plan before doing the hara kiri or "assasinate me" route.

And what would or could the Japanese have done if the US had kept its main battle fleet in San Diego instead of Pearl?

Hit San Diego? No

Not strike South? No

Give in to US demands? No

That kinda leaves a strike south into the PI and Guam and having to deal with the US fleet only when it comes out to meet Tokyo's only option
 
I did not imply that Japan would cave, it would take a collapse of the Japanese economy to do that. Yes the Japanese plan was always for the Mahanian battle between battleships somewhere not too far from Japan, taking advantage of being closer to home, after the Japanese had nibbled at the US fleet going west. The problem is that this meant the US taking of Pacific islands would be much quicker and easier than OTL. Yamamoto realized that this strategy, leaving the US fleet intact from day one and waiting for them was a loser. Using the "old" plan would be worse for Japan than OTLs PH, and much worse than a successful PH.
 
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