"How the Japanese Might Have Easily Improved Their Pearl Harbor Attacks on Dec.7'41"

[Glenn239]

If you look at the official list the Nagumo followed for attack priorities (as established in Annex 3 of Operation Order No. 1, issued on 1 November 1941 (as cited in H.P. Willmott’s Pearl Harbor, p. 64), it is not hard to see where the Third Wave would go: remaining battleships still afloat, and cruisers or other large ships of opportunity in the harbor.

1. Land-based airpower
2. Aircraft carrier
3. Battleships
4. Cruisers and other warships
5. Merchant shipping
6. Port facilities
7. Land installations

WRT this list. The Japanese BDA considered that land based airpower had been hit fairly hard, but Nagumo's HQ via (I think) radio intercepts had determined that many US bombers remained. The carriers (2) were absent. The battleships (3) had been heavily knocked about. (4) and (5) were still plentiful targets, but the IJN dive bomber units were recovering on the afternoon of the 7th. AA was rated as heavy during the 2nd wave over the harbor My guess on a 3rd wave would be something like this -

5th Division (dive) - airfields
1st and 2nd division (dive) - airfields, or many might not even participate due to repairing damage.
1st and 2nd (level bombers x 50) - battleships
1st and 2nd (level bombers x about 30) - port facilities
5th Division (level) - port facilities

 

[Belisarius II]

Which historically ended with firebomb raids and atomic bomb clouds over Japanese cities.

How do they have any hope without oil? Up to late 1944 they had a reasonable amount of oil. Japan started the war thinking they had enough oil to last for 18-24 months of current usage. Burning oil at full blast wartime high consumption, without taking the NEI's oilfields will run through that twice as fast.

 

[Glenn239]

Perhaps because he saw that the reality is that there's enough depth and space for ships to get past a blockship even if it manages to sink itself in exactly the right spot.

From what I recall, I never considered a blockship likely to succeed. An interesting tidbit on that whole project. People often criticize Yamamoto for the complexity and flaws of the Midway plan. But, I found with the Hawaii thing the same thing happening, where a tidal wave of often conflicting details was attempting to distract attention from the key operational details. I was just one guy, so these distractions would get rounded up and re corralled. But I could *totally* see how a group of planners with wildly different ideas and priorities could take even a (comparatively) simple plan like Midway and turn it into a cat rodeo.

Anyway, blockships. I recall these three fundamental rules while drafting the thread. There could have been others, but these are the ones I remember,

1. The carrier attack was the primary focus, a follow-up invasion was secondary. Therefore, nothing for improving the chances of the secondary invasion was allowable if that would unduly threaten the chances for the carrier attack. So, no blockships in part because blockships are muddling about before the attack trying to alert the defenders, in part because blockships do nothing to help the IJN carriers win a carrier battle around Hawaii.
2. The invasion was not an automatic feature. Why bother sending 75,000 troops to Hawaii if the carriers fail? The main invasion only starts if the initial naval battle succeeds. (Some minor prelminary ops intended to help the carriers excepted).
3. If the invasion was cancelled, the forces allocated needed a secondary invasion plan as a backup. This plan was to abort the invasion of Hawaii but seize the sentinel islands of Midway, etc., in preparation for a possible 2nd phase later in 1942.

What I did look into was the possibility of dropping aerial mines to block the channel. However, (and as somebody here has already mentioned), the IJN did not have air-deployable sea mines at this time.

 

[Belisarius II]

Yet historically, the Americans did.

No, they didn't. They had no indication of any Japanese troop ship movements in the North Pacific because there weren't any. The Americans knew where the Japanese landing forces were going to. The Japanese couldn't conceal those operations because they were too large, and complex.

 

[Athelstane]

The general 'deception' breaks down the bigger the forces involved become.

Cannot emphasize this enough!

 

[rascal1225]

How do they have any hope without oil? Up to late 1944 they had a reasonable amount of oil. Japan started the war thinking they had enough oil to last for 18-24 months of current usage. Burning oil at full blast wartime high consumption, without taking the NEI's oilfields will run through that twice as fast.

With the USN'S Pacific Fleet pretty much destroyed during an AH invasion of Oahu starting on Dec.7'41 exactly who is going to stop the IJN and IJA from walking all over the DEIs at great speed ?

 

[Sekhmet_D]

What I did look into was the possibility of dropping aerial mines to block the channel. However, (and as somebody here has already mentioned), the IJN did not have air-deployable sea mines at this time.

Even if they did, they would have probably pooh poohed such a plan as insufficiently aggressive in the grand samurai tradition.

 

[Glenn239]

Some other questions that come to mind re the invasion Oahu scenario:

How long will it take the invading divisions to secure the Hawaiian Islands? Will the KB stay on station for that whole time? If so, how? With convoys of oilers shuttling from Japan? If the KB does not stay on station, who supplies air cover? Light carriers running shifts from the Marshalls?

Thumbs up, what a great series of questions. They're exactly the details I remember trying to wrangle with. Here's the answers I came up with back then.

How long will it take the invading divisions to secure the Hawaiian Islands? Will the KB stay on station for that whole time? If so, how? With convoys of oilers shuttling from Japan? If the KB does not stay on station, who supplies air cover? Light carriers running shifts from the Marshalls?

The time it takes to seize the Hawaiian Islands depends on the plan of attack (siege vs direct assault). A siege scenario could take several months. KB could not stay on station all that time, but would have to return to base once or twice. An early direct assault would be difficult to coordinate with the initial carrier assault and so was highly inadvisable - it would confuse the IJN carriers between two missions. This too implied a plan where after a carrier attack, the carriers return to base, then return with the invasion assault waves - so still a number of weeks.

The size of the oiler train depends on the size of the IJN fleet at Hawaii, especially if the battleships were thrown into the mix. Generally speaking, I found in order to get serious about an attack, the IJN needed not only the bulk of its oilers, but its tankers as well, with the tankers required to refuel the oilers and then shuttle back to Japan for more. WRT the carriers, the weakness was avgas and ordnance stores. The carriers had about 3 days of heavy fighting in them. The battleships had only a number of days mucking about near Oahu, so if a naval battle was not in offering a bombardment was pretty much the only game in town.

With the carriers unable to remain at Oahu, for an attack to succeed land based air elements would have to be set up on the outer islands. This was not assured, and the necessary land based air were double-employed at Luzon. Light carriers could have shuttled some aircraft.

Is land based aircraft ferrying from the Japanese Mandates part of the equation? If so, how will they get fuel and ordinance, spare parts etc? More convoys?

Yes and yes. A G4M could carry 1,800lbs in bombs and might burn maybe 4,000lbs of gas in a typical mission in this region. About 3 tons. Scale that up to 60 bombers for a month and it's about 6,000 tons of supply. Add in the seaplanes and the fighters, and it's maybe 12,000 or 15,000 tons.

Do the Japanese count on using fuel oil, avgas etc. captured in Hawaii?

No.

 

[Glenn239]

Even if they did, they would have probably pooh poohed such a plan as insufficiently aggressive in the grand samurai tradition.

I thought they could probably have MacGyvered an air dropped mine of some sort, but nothing that US minesweeping forces couldn't quickly handle. So I thought neither air dropped mines or blockships would work. My conclusion overall was that to block the entrance to the harbor, the Japanese needed to take Honolulu by assault and then set up artillery and mines at the entrance. Honolulu falls, and if the outer islands are occupied, it's game over, the island will fall because without a harbor, the garrison and population cannot feed itself.

 

[rascal1225]

WRT this list. The Japanese BDA considered that land based airpower had been hit fairly hard, but Nagumo's HQ via (I think) radio intercepts had determined that many US bombers remained. The carriers (2) were absent. The battleships (3) had been heavily knocked about. (4) and (5) were still plentiful targets, but the IJN dive bomber units were recovering on the afternoon of the 7th. AA was rated as heavy during the 2nd wave over the harbor My guess on a 3rd wave would be something like this -

5th Division (dive) - airfields
1st and 2nd division (dive) - airfields, or many might not even participate due to repairing damage.
1st and 2nd (level bombers x 50) - battleships
1st and 2nd (level bombers x about 30) - port facilities
5th Division (level) - port facilities

I didn't think that the Kido Butai carried more than the 1st Wave's load of 800kg AP bombs because more than that were not made before the Kido Butai left Japanese waters ? Or was that the shallow water torpedoes ?

 

[Sekhmet_D]

With 82 years of hindsight, we know that now but the Japanese could not know that Hitler was sinking Allied tankers at an astonishing rate ...

Of course they could. A simple phone call to their man in Berlin, Hiroshi Oshima, could have gleaned them that information.

 

[rascal1225]

Of course they could. A simple phone call to their man in Berlin, Hiroshi Oshima, could have gleaned them that information.

True but not the reverse of that information ... exactly how many tankers/oilers of what capacity could the Americans scrape together on short notice to supply a Pacific Fleet thrust at Japan ?

 

[Belisarius II]

With the USN'S Pacific Fleet pretty much destroyed during an AH invasion of Oahu starting on Dec.7'41 exactly who is going to stop the IJN and IJA from walking all over the DEIs at great speed ?

The Pacific Fleet was pretty much taken out of action as far as interfering with the Japanese invasion of SEA by the Pearl Harbor raid. Even without that there wasn't much they could directly do about it. This operation is delaying that invasion indefinitely. While Japan is wasting time and resources in Hawaii the ABDA powers would be strengthening their defenses in SEA. The British would mass the Eastern Fleet and move it to Singapore. With the IJNAF tied down in Hawaii do they even sink Force Z? Do they invade Malaya, the Philippines, or Burma? Do they occupy Rabaul? By sending 4 divisions to Oahu there aren't enough transports for any other amphibious operations of any scale.

 

[Belisarius II]

Of course they could. A simple phone call to their man in Berlin, Hiroshi Oshima, could have gleaned them that information.

The Germans didn't know the Japanese were going to attack Pearl Harbor, and neither did Oshima. If they did the American would've known about it, because the Japanese ambassador's cables to and from Japan were being read by Magic. Hitler declared war on an impulse. Launching a U-Boat Blitz was a Sper of the moment operation. "Drumbeat" was not planned before the war, and no one could've known it would be so successful.

 

[YYJ]

I didn't think that the Kido Butai carried more than the 1st Wave's load of 800kg AP bombs because more than that were not made before the Kido Butai left Japanese waters ? Or was that the shallow water torpedoes ?

The shallow water torpedoes were in very limited supply. Akagi delayed sailing with the main force so she could load more, and had to catch up.

Now the problem was producing enough of the modified Kai 2 torpedoes for the attack. Japan produced Type 91 torpedoes in the Nagasaki Weapons Factory operated by Mitsubishi Heavy Industries. Its production schedule would not make enough torpedoes available until the end of November.[72] That would be too late. Mitsubishi would not permit overtime work, and the factory’s manager, Yukio Fukuda, could not be told about the dire time need for the final torpedoes.[73] However, Fukuda was able to read between the lines. He authorized the overtime.[74] Even so, only 50 of the torpedoes were available when the fleet sailed for Hitokappu Bay, where they would sortie against Pearl Harbor. Akagi remained behind to receive the final batch. Akagi reached the fleet on November 24, only two days before the fleet steamed out of the bay.[75]

Pearl Harbor: Thunderfish In The Sky

When an aerial torpedo weighing almost two tons slams into the water at 200 mph, it barely slows down. In the open sea, Japan’s aerial torpedoes plunged 150 feet before climbing back to attack depth.[1] Pearl Harbor was only about 40 feet deep,[2] so Japan needed to modify its tactics and...

www.pearlharboraviationmuseum.org

 

[Sekhmet_D]

The Germans didn't know the Japanese were going to attack Pearl Harbor, and neither did Oshima. If they did the American would've known about it, because the Japanese ambassador's cables to and from Japan were being read by Magic. Hitler declared war on an impulse. Launching a U-Boat Blitz was a Sper of the moment operation. "Drumbeat" was not planned before the war, and no one could've known it would be so successful.

The Germans didn't, of course. But what I'm saying is that the Japanese could have found out about their friends' fearsome submarine efficiency during the 'First Happy Time' in the North Atlantic very easily, and crunched some numbers from there.

 

[Dorknought]

Haruna and Kongo were not battleships. They were battlecruisers. An important distinction.

Even if you ignore that distinction, this was nearly a year earlier, before the IJN had gotten its face bashed in at Midway and been forced to rework its naval doctrine from the ground up to put the carrier center-stage rather than the big gun platforms.

I'm sure if you were sheltering in a foxhole at Henderson Field with 14" rounds coming in, this information would be so reassuring to those also in the same foxhole.

After they were reconstructed the Kongo class were considered Battleships by the IJN.

 

[Sekhmet_D]

I'm sure if you were sheltering in a foxhole at Henderson Field with 14" rounds coming in, this information would be so reassuring to those also in the same foxhole.

After they were reconstructed the Kongo class were considered Battleships by the IJN.

Indeed. Potayto, potahto.

 

[Sekhmet_D]

During the attack on Pearl Harbor itself, there were instances when Japanese pilots declined to bomb or even strafe the oiler Neosho, deeming it an unworthy target. Yet there are many cases where the Japanese pilots did attack targets that were higher on the priority list, even in cases where those attacks were of questionable worth. For instance, Zimm makes the very strong case that the second wave dive-bombers expending much of their attacking power on attacking the USS Nevada was a poor usage of their combat power, in that their bombs were poorly suited to attacking a heavily armored target like a battleship. Yet when presented with a moving target that fit their mental model of what constituted an important target (“That’s a battleship!”) they attacked it instead, and Fuchida (as force commander) did nothing to stop them.​

I wouldn't really call this a 'very strong case'. I would call it 'absolute fact' instead. Under normal fighting circumstances, Nevada would have handily shrugged off dive bomber ordnance the way South Dakota did at Santa Cruz.

 

[Grand Admiral Thrawn]

I'm sure if you were sheltering in a foxhole at Henderson Field with 14" rounds coming in, this information would be so reassuring to those also in the same foxhole.

After they were reconstructed the Kongo class were considered Battleships by the IJN.

Setting aside that US Marines don't determine the naval doctrine of the IJN, and also that the size of the rifle round didn't determine if a ship as a battleship or battler-cruiser (like the Dreadnought/Invincible class show), the fact the Kongos were assigned the role of night fighting in the Kantai Kessen with the cruisers and destroyers, and not waiting with the battle-line, show the IJN considered them not battleships.

It would make them more malleable to use them in a shore bombardment which might suffer losses, however.