Dec 7, 1941. The USN is at sea. What does IJN do now?

Admiral Beez

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Dec 4, 1941, the USN sails from Pearl Harbour to conduct a fleet exercise in the vast ocean between it and the US mainland. Dec 7, 1941, battleships USS Arizona, Nevada, Oklahoma, Tennessee, California, Maryland, and West Virginia, along the cruisers USS New Orleans, San Francisco, Raleigh, Detroit, Phoenix, Honolulu, St. Louis, and Helena, twenty destroyers plus six fleet supply ships are located about two hundred miles to the south west of the Haiwan Islands. Remaining in Pearl Harbour are ten destroyers, plus a multitude of lesser craft like minesweepers, plus submarines.

Dec 7, 1941. Nagumo arrives. What are his targets?
 

Admiral Beez

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See above.
Plus the U.S. still loses a bunch of planes.
True. But I don’t think the fuel barns were ever a target. The IJN didn’t seem to grasp their importance. So, the IJNAS arrives and shoots up the airfields and torpedoes whatever ships they can find, sinking some destroyers and auxiliary ships, and USS Utah takes every frustrated Kate and Val pilots’ attention.
 

GrauGeist

Generalfeldmarschall zur Luftschiff Abteilung
They attack the Pennsylvania and other ships (minelayers, minesweepers, cutters, etc.) and now concentrate more on shore facilities like the drydocks and air fields as well as the oil tank farms, especially since the additional AA historically provided by the warships is no longer there.

The planned third wave was to have targeted the drydocks and oil storage facilities. Not having the bulk of the U.S. fleet present would have most likely seen this happen.
 

Glider

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Hit the port as hard as you can with the first wave and then go and find the ships at sea. The biggest loss possible to the USN is the men on the ships, not the ships. At sea without the support of the land bases, they would be very vulnerable.
The crews and ships themselves will not have the full war complement and the IJN would have a huge advantage
 

SaparotRob

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They attack the Pennsylvania and other ships (minelayers, minesweepers, cutters, etc.) and now concentrate more on shore facilities like the drydocks and air fields as well as the oil tank farms, especially since the additional AA historically provided by the warships is no longer there.

The planned third wave was to have targeted the drydocks and oil storage facilities. Not having the bulk of the U.S. fleet present would have most likely seen this happen.
I forgot all about U.S.S. Pennsylvania. Now where did I leave my brain?
 
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Thumpalumpacus

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Tejas
Given Nagumo's conservative nature, after the first wave finds the harbor empty, KdB recovers the first strike, sends out searches and attacks if quarry is spotted. If quarry is not spotted, they get the hell out. I can't see Nagumo hanging around for strikes on an empty base, even with all the infrastructure vulnerable.

If he finds the OBBs at sea, he launches everything and the kitchen sink, but if they're exercising between Pearl and the mainland they won't be 200 mi SW of Oahu, they'll be east-by-north and fuel for the Japanese ships is definitely going to hamper an attack at sea.
 

Admiral Beez

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If he finds the OBBs at sea, he launches everything and the kitchen sink, but if they're exercising between Pearl and the mainland they won't be 200 mi SW of Oahu, they'll be east-by-north and fuel for the Japanese ships is definitely going to hamper an attack at sea.
That‘s my bad geography. I meant NE of Oahu, 200 mi and growing. My idea is that Nagumo doesn’t find them. Does the USN’s improved status give the US better chances in the Philippines?

And just for giggles, Force Z has also survived in this thread too. The IJNAS has had an unlucky 48 hours.
 

Thumpalumpacus

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That‘s my bad geography. I meant NE of Oahu, 200 mi and growing. My idea is that Nagumo doesn’t find them. Does the USN’s improved status give the US better chances in the Philippines?

I doubt it. Slow fuel-hogs that have to get within 10 miles of a target vs fast fuel-hogs that can strike at 200 miles or leave, or maneuver, as they saw fit?

The Philippines weren't going to be saved in 41/42 no matter what because Japan could apply power faster, against a weaker opponent with very poor theater leadership. They seized air supremacy on the first day of hostilities there. They already had control of the seas. And the OBBs cruised at what, 14kts? We're not even talking about the time it would take to organize a rescue convoy.

And just for giggles, Force Z has also survived in this thread too. The IJNAS has had an unlucky 48 hours.

The Japanese had significant forces in SEA to deal with them, and as I've written elsewhere, if Zed survives, the smart money is retreating to Ceylon. Trying to thread the Indonesian needle to join up with the Americans? Let me know how that works out, between the lack of air cover and Repulse's range limitations.
 

Admiral Beez

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I doubt it. Slow fuel-hogs that have to get within 10 miles of a target vs fast fuel-hogs that can strike at 200 miles or leave, or maneuver, as they saw fit? if Zed survives, the smart money is retreating to Ceylon.
I agree, Force Z runs for Ceylon. However it will be an odd section in future history books and naval academy classes where it’s reported that both the USN and RN’s battlefleets survived the first days of the Pacific War, and then spent the next three months staying out of harms way while the Japanese gobbled up the Philippines, Malaya, Burma, and DEI.
 

muskeg13

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There are several possibilities, but most likely there is no Pearl Harbor attack. The intent of the mission is to cripple the Pacific Fleet to entice the U.S. to sue for peace or at least prevent any meaningful opposition for at least 6 months. With the fleet absent, including all of the carriers, and without knowing where the fleet is or when it's returning, Nagumo would be recalled. He was receiving (one-way) instruction and intelligence updates from Tokyo daily. The intel updates were current within 12-24 hours, provided by the Japanese consulate in Honolulu to Tokyo and then relayed to Nagumo.

The Japanese would redouble their efforts to locate the Pac Fleet or try and determine if it would return to Hawaiian waters (including the Lahaina alternate fleet anchorage) before the Kido Butai would run so low on fuel that they'd be forced to go home without a fight, but Nagumo was also under strict orders not to be detected himself before launching the planned attack, so Japanese search efforts would need to be very careful. At some point, the decision would probably be made to abort the attack on Hawaii if there wasn't a high probability of the main targets being located within striking range. Kido Butai assets would be preserved for later employment.

Striking a handful of small warships and auxiliaries, shooting up several airfields and bombing docks and warehouses means the main mission has failed. It's not worth the risk involved for such a small pay-out. The Kido Butai was neither trained nor equipped to do more than superficial damage, at best, to the port facilities or the naval fuel tank farm.

Hitting Wake or Midway on the run home is a possibility, but either strike would probably be "one and done" missions, given the fuel status and less than useful Pearl Harbor/Pac Fleet specific ammunition load out.
 

Admiral Beez

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There are several possibilities, but most likely there is no Pearl Harbor attack.… the Kido Butai would run so low on fuel that they'd be forced to go home without a fight,
What about the simultaneous attacks on Malaya, the Philippines and DEI? Can these still be canceled when Nagumo comes up craps?
 

Admiral Beez

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The Pennsylvania wasn't docked on Battleship Row, but berthed near the Navy yard - ironically, within walking distance of one of the oil tank farms
I meant to ship out all the BBs but forgot about USS Pennsylvania and Utah. For my purposes, there are no battleships at Pearl.
 

muskeg13

Airman 1st Class
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May 8, 2012
What about the simultaneous attacks on Malaya, the Philippines and DEI? Can these still be canceled when Nagumo comes up craps?
No. Just PH is scrapped. The Japanese would then be able to reallocate more assets to achieving their other objectives even quicker. I'm not sure of the exact hourly timelines for the other major operations, but they were already well underway, and the conquest (and exploitation) of Malaya and the DEI were absolutely necessary for the Empire to survive. The Philippines and PH were actually supporting operations to ensure success in Malaya and DEI.
 

GrauGeist

Generalfeldmarschall zur Luftschiff Abteilung
The Utah was a training ship and demilitarized, so would not have sailed with the fleet.

Also, for this scenario, you need to choose about two-thirds (or so) of the fleet's numbers for the fleet exercise, as the USN does not commit an entire fleet, but holds a percentage in reserve.

So the Pennsylvania being in Harbor that morning would be legit.
 

EwenS

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There are several possibilities, but most likely there is no Pearl Harbor attack. The intent of the mission is to cripple the Pacific Fleet to entice the U.S. to sue for peace or at least prevent any meaningful opposition for at least 6 months. With the fleet absent, including all of the carriers, and without knowing where the fleet is or when it's returning, Nagumo would be recalled. He was receiving (one-way) instruction and intelligence updates from Tokyo daily. The intel updates were current within 12-24 hours, provided by the Japanese consulate in Honolulu to Tokyo and then relayed to Nagumo.

The Japanese would redouble their efforts to locate the Pac Fleet or try and determine if it would return to Hawaiian waters (including the Lahaina alternate fleet anchorage) before the Kido Butai would run so low on fuel that they'd be forced to go home without a fight, but Nagumo was also under strict orders not to be detected himself before launching the planned attack, so Japanese search efforts would need to be very careful. At some point, the decision would probably be made to abort the attack on Hawaii if there wasn't a high probability of the main targets being located within striking range. Kido Butai assets would be preserved for later employment.

Striking a handful of small warships and auxiliaries, shooting up several airfields and bombing docks and warehouses means the main mission has failed. It's not worth the risk involved for such a small pay-out. The Kido Butai was neither trained nor equipped to do more than superficial damage, at best, to the port facilities or the naval fuel tank farm.

Hitting Wake or Midway on the run home is a possibility, but either strike would probably be "one and done" missions, given the fuel status and less than useful Pearl Harbor/Pac Fleet specific ammunition load out.
As well as the accurate information coming from the Japanese Intelligence Officer in their legation in Pearl Harbor, on the morning of the strike the cruisers Tone and Chikuma each launched a floatplane pre-dawn to reconnoiter the anchorage at Lahaina Roads and also Pearl Harbor itself respectively. They were scheduled to arrive just after first light. Chikuma’s aircraft reported back to the KB between the launch of the first and second waves.

So even last minute sailings from PH could have been detected and the plan changed.

There is a point made by Zimm in his book “Attack on Pearl Harbor. Strategy, Combat, Myths, Deceptions” about Japanese inflexibility in their planning. He notes that the allocation of B5N2 aircraft between torpedo and level bombing roles had been decided 3 months before and the crews trained accordingly. Subsequent new intelligence that should perhaps have led to a different allocation was not used.

So in the event of the US Fleet not being in PH there would be difficulty switching the roles of these aircraft and thereby favouring a decision to withdraw without striking.

He also considers what would have happened had the US fleet had advance warning and sortied before the Japanese struck. The conclusion is that the attack would have been less successful in terms of ships sunk/damaged and Japanese aircraft losses higher. However exact numbers vary according to a variety of factors.

He also deals with the subject of a second raid / third wave to attack the harbour facilities on pages 301-325.

His conclusion was that an attack on the Navy Yard facilities by the Japanese would not inflict debilitating damage when you take account of the considerable “restorative capacity” available both ashore and afloat (various depot & repair ships being present) and using both civilian and military resources.

As for the fuel tank farm, the tanks themselves were not that easy to destroy. He cites Italian attempts to shell the refinery at Haifa and I would highlight the initial Darwin raid in Feb 1942. He also notes that by 7 Dec 1941 some of the then secret underground storage was complete and at least partially filled. How long to replenish stocks would depend on the priority allocated to the task in the US merchant tanker fleet. How long to build new tanks? Again the question of priority for the necessary steel (est 5,000 tons to replace them all) and construction crews.
 

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