What if the Japanese had brought an invasion force to take Hawaii after Pearl Harbor?

well if your not going to invade then they should at least pound the place harder than they did, since while they sank some boats and did some damage, it wasn't nearly enough of a set back, or ignore it all together and save face to bring them to you to fight on your terms on the open sea, oops they tried that too

This is one those cases IMO where they obviously picked the wrong move, but it was still the best option open if we accept the basic premise.
I.e. We can't surrender and can't buy what we need. Therefore we must take it. Therefore we must stop the Americans from severing supply lines. Therefore the Pacific fleet must be destroyed, etc.

I kind of doubt trying to hit Pearl harder would have worked. Their planes would face more prepared defenders, costing more aircraft and pilots who couldn't be spared. Naval bombardment puts the ships (which are needed elsewhere) at risk, and they don't have the fuel to stay on-site. They could try to of course, and thinking about the changes from there would probably be interesting. It just wouldn't accomplish something.

Edit: to put it another way: the winning move was not to play, but of the losing moves the OTL one was probably the best option.
 
There wasn't an actual plan for going in with a third wave anyhow, nor did they think it necessary given the BBs mostly being thrashed and the carriers out at sea. Meanwhile you've tied your fleet to Japan (somehow; the logistics of that, never Japan's strong point, are going to be ever so fun), you've got a couple of carriers and various subs cheerfully looking for you which is going to make your fleet nervous and vulnerable to attack.

Right, Nagumo probably had no plans for a third wave. This was news to his aviators, that thought, having sailed 14 days across the Pacific, they'd be in combat for at least the rest of the day. As for his staff, his division admirals (Yamaguchi, Hara) had no idea on his intentions, his chief (Kusaka) was probably aware that they'd withdraw, and Genda (air operations) probably had an idea, if not knowing for certain. As for US subs and carriers - if Nagumo seriously had withdrawn out of fear of these, he'd have been cashiered upon his admission as unfit for command, (he was careful to frame his reason formally as the accomplishment of his orders).

And going all out at Hawaii doesn't win them the war either because it's a forward outpost, just like taking the Philippines didn't end the war. You can take out every single ship that the USN had at Hawaii and the US would still retain a powerful fleet and have vastly more combat power available to them within two years and there's no reason to think that they would be willing to do a negotiated peace given how pissed off they were just for OTL Pearl.

"No reason to think" sounds strangely quite vague in a paragraph that otherwise is pretty sharp on its editorial content. It is quite likely such a choice would not cause a negotiated peace. But going for the NEI was certain to fail, so the Southern Operation was a chimera.

Meanwhile this invasion plan leads to ABDA actually becoming a meaningful force (possibly with French Indochina allying with them) while Japanese forces are stuck dying horribly in the attempted invasion of the Hawaiians which means that even if you get a negotiated peace out of the US, you still don't get the oil you want and your economy dies in 1942 due to lack of oil (due to increased consumption from a major naval conflict).

The Japanese will lose a long war whether they had the NEI or not, so the NEI was actually irrelevant to the outcome.

Congratulations, you've lost an even shorter war for Japan.

Who gives a shit about losing a "shorter" war? It's either win or lose. There's no prize for an extended timeline.
 

Delta Force

Banned
A alternate plan proposed was for a small 5,000 man shock unit to storm ashore & attempt to rip through the unready defense in a few hours. A few fast transports & some cruisers would comprise the amphibious group. Sort of a coup de main with low odds of sucess. The attraction is it only throws away a half dozen ships & a couple SNLF or army regiments.

What if the Japanese pulled a page from Cold War doctrine and infiltrated special forces into Hawaii to attack high value targets? Could they hide even a few dozen special forces in the cargo bay of freighters docked in Hawaii, California, and Panama and have them all emerge to carry out simultaneous attacks, perhaps even literally using false markings and false flags on the freighters to help with the infiltration? Maybe they could (as an additional or alternate plan) sink ships in key areas to render them impassable or at least slow down shipping traffic.
 
Also the only way for Japan to win in the Pacific would be to force a peace with the US and taking Hawaii might be enough to shock the US to the negotiation table.
What? Hawaii isn't even a US state. That's exactly the flawed thinking that got Japan into trouble in the first place. The US would never be forced to the negotiation table.
 
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Ships or
What if the Japanese pulled a page from Cold War doctrine and infiltrated special forces into Hawaii to attack high value targets? Could they hide even a few dozen special forces in the cargo bay of freighters docked in Hawaii, California, and Panama and have them all emerge to carry out simultaneous attacks, perhaps even literally using false markings and false flags on the freighters to help with the infiltration? Maybe they could (as an additional or alternate plan) sink ships in key areas to render them impassable or at least slow down shipping traffic.

Ships originating in Japan & calls from Japanese flagged ships ceased when the embargos went into effect the previous summer. A very large portion of the others were controled by Britain = Greek, Norwegian, Dutch... & all were vetted by the local port defense. As we know the defense command on Oahu were very concerned about sabotoge. Cargo ships had their papers authenticated, and inspected. The port authorities weren't waving unknown cargo ships through the channel. Or the Panama locks for that matter.
 
a few things...

there is only one major anchorage (Pearl Harbor) and 2 substantially smaller ports (in terms of anchorage space)(Hilo and Honolulu) in the Hawaiian chain extending all the way out to Midway (which with Midway and French Frigate Shoals gives you two even smaller anchorages). American coastal defenses and the garrison of 4 Regular Army regiments (the Hawaiian Division had just split into 2 triangular divisions in 1941, but the other two regiments weren't there yet), plus the coast defense artillery command (several forts as previously shown). Plus there is a Army National Guard regiment, an engineer regiment, several battalions of field artillery, and assorted other units. Plus sufficient Marines could be grouped together to form a couple of ad hoc battalions if they run out of aircraft and ships. So basically 4 reinforced combat brigades and while Short didn't understand airpower, he was an infantryman and did well in the Army schools prewar. Usual requirement is 3:1 to attack, so the Japanese need 12 combat brigades, plus of course even they need some logistical units.

The best beach is right into the teeth of a US Army coast defense fort (Debussy). The North Shore in winter is known for its impressively large waves (hence the reason for surfing championships there in January), so the actual landing sights are fewer than you might think.

Hilo has a relatively minor port in 1941, and a new airfield with limited facilities (recently expanded). It has a small garrison (as does some of the other islands like Kaui). It is also 212 miles to Honolulu to Hilo, so adding yet more distance here. There are also small ports at Kaui and Maui. Airfields are barely more than emergency airstrips other than on Oahu and Hawaii

So while taking the outlying islands would seem to provide bases, they only do if the Japanese bring the needed engineers and everything else that is required to build those bases.

There are plenty of other issues, but those are good ones that would make a planner think long and hard about this. The IJA doesn't have 12 combat brigades to spare (4 divisions basically), nor a spare field army headquarters to support them (and two divisions normally is a Japanese Field Army, not 4). The Navy doesn't have the transport fleet to move them unless the Philippines and Malaya operations are cancelled (which is where all the transports are for this size a lift). It would take an enormous amount of oil to fuel all these ships, plus their escorts, plus the battleships needed for the fire support force (one per division would be reasonable plus their escorts too). In effect, it would take the entire fleet that moved on Midway Island, including all the carriers, and every available tanker and transport.

Which means at best the Japanese hold Hawaii but don't have anything else

But to move on from that...

The majority of food for the military and civilian population has to be imported in 1941. No wheat, damn little rice, and while there is plenty of tropical fruit for a short time that is a short term solution. No oil, no coal, and some islands don't even have all that much in the way of forest so firewood is an issue. No medical supplies, spares etc... the list goes on and on

So everything pretty much has to be imported, and from a distance twice as far from Hawaii as North America is.

If the Japanese could somehow take it they couldn't do anything else. The Army would never agree and the Navy could never support it. It would take a huge chunk of the Japanese merchant marine just to keep a garrison supplied even if the outer island strategy is used and no immediate attempt is made on Oahu.

and one last thing... the Chief of Staff of the Hawaiian Department (Army) is Lawton Collins, one of the better combat commanders of the US Army in World War II.
 
What if the Japanese pulled a page from Cold War doctrine and infiltrated special forces into Hawaii to attack high value targets? Could they hide even a few dozen special forces in the cargo bay of freighters docked in Hawaii, California, and Panama and have them all emerge to carry out simultaneous attacks, perhaps even literally using false markings and false flags on the freighters to help with the infiltration? Maybe they could (as an additional or alternate plan) sink ships in key areas to render them impassable or at least slow down shipping traffic.

I think if memory serves that was one of the few things General Short had focused on, to the extent that planes were parked in the open where they could be seen and there were presumably plenty of sentries and guards around. So in Hawaii it would likely have failed, not sure on the others. Panama might have been more promising?
 
a few things...

there is only one major anchorage (Pearl Harbor) and 2 substantially smaller ports (in terms of anchorage space)(Hilo and Honolulu) in the Hawaiian chain extending all the way out to Midway (which with Midway and French Frigate Shoals gives you two even smaller anchorages).

There were two major (fleet) anchorages in Hawaii, Pearl Harbor and Lahaina Roads, Maui. Nagumo scouted both locations just before the attack and the first wave was prepared to go to Maui if the US battlefleet had been anchored there. Pearl Harbor was superior to Lahaina because it was a protected anchorage.

American coastal defenses and the garrison of 4 Regular Army regiments (the Hawaiian Division had just split into 2 triangular divisions in 1941, but the other two regiments weren't there yet), plus the coast defense artillery command (several forts as previously shown). Plus there is a Army National Guard regiment, an engineer regiment, several battalions of field artillery, and assorted other units. Plus sufficient Marines could be grouped together to form a couple of ad hoc battalions if they run out of aircraft and ships. So basically 4 reinforced combat brigades and while Short didn't understand airpower, he was an infantryman and did well in the Army schools prewar. Usual requirement is 3:1 to attack, so the Japanese need 12 combat brigades, plus of course even they need some logistical units.

12 brigades for a direct assault on the southern shore seems about right, but for the occupation of key positions on the outlying islands, more like 2 brigades. Since the point would be to lure in the US carriers and sink them, sending 12 brigades onto Oahu would be silly - you can't take Pearl Harbor by storm and then expect USS Hornet to come charging in from the Atlantic? No way. So you send the 2 brigades into the outlying islands, set up the blockade of Oahu. Now Hornet, Wasp, Saratoga, and Yorktown have a choice to make, right?

The best beach is right into the teeth of a US Army coast defense fort (Debussy). The North Shore in winter is known for its impressively large waves (hence the reason for surfing championships there in January), so the actual landing sights are fewer than you might think.

The surf at Oahu is determined by the prevailing winds (direction and speed) that day. In December the north shore rarely is good for landings - maybe a few days a month. The south shore usually was good, the east and west shore maybe half the time, combined, (but if one was good for a landing, the other was probably bad). The net effect is that you don't sail to Hawaii in December 1941 and just expect to land on the east coast on a given day.

Hilo has a relatively minor port in 1941, and a new airfield with limited facilities (recently expanded). It has a small garrison (as does some of the other islands like Kaui). It is also 212 miles to Honolulu to Hilo, so adding yet more distance here. There are also small ports at Kaui and Maui. Airfields are barely more than emergency airstrips other than on Oahu and Hawaii. So while taking the outlying islands would seem to provide bases, they only do if the Japanese bring the needed engineers and everything else that is required to build those bases.

Seaplanes don't need airfields.

The Army was in the process of building B-17 bases on all the major outlying islands. It is known that some of these were at least partly operational, because the B-17's at Oahu were dispersed into the outer islands after the attack (If a field can operate B-17's, the Japanese could use it for anything in their inventory.) The navy also had other fields, (such as Puunene) that could operate a carrier wing. Various civilian fields suitable for the lighter aircraft the Japanese flew, (a Zero does not need the takeoff room of a B-17).

The IJA doesn't have 12 combat brigades to spare (4 divisions basically), nor a spare field army headquarters to support them (and two divisions normally is a Japanese Field Army, not 4). The Navy doesn't have the transport fleet to move them unless the Philippines and Malaya operations are cancelled (which is where all the transports are for this size a lift).

Malaya could have proceeded, Philippines could not have.

It would take an enormous amount of oil to fuel all these ships, plus their escorts, plus the battleships needed for the fire support force (one per division would be reasonable plus their escorts too). In effect, it would take the entire fleet that moved on Midway Island, including all the carriers, and every available tanker and transport.

Figure on at least a million tons of fuel spent for a Hawaii campaign. Maybe even two.

Which means at best the Japanese hold Hawaii but don't have anything else.

So if the Americans were defeated at Hawaii and thrown back to California, the Dutch are then going to hold the Japanese back with a cease and desist order or something? Gandalf sitting on the beach at Java wielding his staff, shoutin, "you shall not pass!"?


The majority of food for the military and civilian population has to be imported in 1941. No wheat, damn little rice, and while there is plenty of tropical fruit for a short time that is a short term solution. No oil, no coal, and some islands don't even have all that much in the way of forest so firewood is an issue. No medical supplies, spares etc... the list goes on and on

So everything pretty much has to be imported, and from a distance twice as far from Hawaii as North America is.

Correct, Oahu was extremely vulnerable to siege tactics.

If the Japanese could somehow take it they couldn't do anything else. The Army would never agree and the Navy could never support it. It would take a huge chunk of the Japanese merchant marine just to keep a garrison supplied even if the outer island strategy is used and no immediate attempt is made on Oahu.


One of the factions arguing against Hawaii used that tact, which was that Hawaii would require about 30 supply ships, (180,000 tons) supply per month of the civilian population. That worked out to 6,000 tons per day for about 500,000 people, or 24lbs per person per day. A realistic figure might have been 1lbs per person per day support, about 2 supply ships per month.
 
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There were two major (fleet) anchorages in Hawaii, Pearl Harbor and Lahaina Roads, Maui. Nagumo scouted both locations just before the attack and the first wave was prepared to go to Maui if the US battlefleet had been anchored there. Pearl Harbor was superior to Lahaina because it was a protected anchorage.



12 brigades for a direct assault on the southern shore seems about right, but for the occupation of key positions on the outlying islands, more like 2 brigades. Since the point would be to lure in the US carriers and sink them, sending 12 brigades onto Oahu would be silly - you can't take Pearl Harbor by storm and then expect USS Hornet to come charging in from the Atlantic? No way. So you send the 2 brigades into the outlying islands, set up the blockade of Oahu. Now Hornet, Wasp, Saratoga, and Yorktown have a choice to make, right?



The surf at Oahu is determined by the prevailing winds (direction and speed) that day. In December the north shore rarely is good for landings - maybe a few days a month. The south shore usually was good, the east and west shore maybe half the time, combined, (but if one was good for a landing, the other was probably bad). The net effect is that you don't sail to Hawaii in December 1941 and just expect to land on the east coast on a given day.



Seaplanes don't need airfields.

The Army was in the process of building B-17 bases on all the major outlying islands. It is known that some of these were at least partly operational, because the B-17's at Oahu were dispersed into the outer islands after the attack (If a field can operate B-17's, the Japanese could use it for anything in their inventory.) The navy also had other fields, (such as Puunene) that could operate a carrier wing. Various civilian fields suitable for the lighter aircraft the Japanese flew, (a Zero does not need the takeoff room of a B-17).



Malaya could have proceeded, Philippines could not have.



Figure on at least a million tons of fuel spent for a Hawaii campaign. Maybe even two.



So if the Americans were defeated at Hawaii and thrown back to California, the Dutch are then going to hold the Japanese back with a cease and desist order or something? Gandalf sitting on the beach at Java wielding his staff, shoutin, "you shall not pass!"?




Correct, Oahu was extremely vulnerable to siege tactics.




One of the factions arguing against Hawaii used that tact, which was that Hawaii would require about 30 supply ships, (180,000 tons) supply per month of the civilian population. That worked out to 6,000 tons per day for about 500,000 people, or 24lbs per person per day. A realistic figure might have been 1lbs per person per day support, about 2 supply ships per month.

the Roads is vulnerable to submarine attack (and stopped being used as a major anchorage for the Pacific Fleet early in 1941 for that reason) and doesn't give you much of an island base. Lanai is a glorified pineapple plantation with a small airport (5000 ft runway now) which may or may not have been present then. Maui does have useful land area but again we run into the need to haul everything from Japan to construct a base. In World War II building advanced bases was not a Japanese strong suit, with Rabual being the rare exception.

As to the blockade, it would rapidly be questionable as to who was blockading whom ... the oil requirements alone for routine voyages from Japan to Hawaii would be daunting. The Americans are awash in the stuff (in fact its handy as its extracted in California) while the Japanese have a very limited stockpile to fuel ALL operations that they must conduct in order to get the oil in the East Indies in order continue to function.

An adult human eats about 2-3 pounds of food a day, setting aside packaging. That doesn't count literally everything else, from medical supplies to cloth to other basic requirements. While the Japanese may not care if the civilians starve (and clearly based on their World War II track record that is a low priority for them), they do care if their garrison starves.

Plus you are talking about hauling aviation fuel, lubricating oil, spare parts, replacement airframes, ammunition, and literally everything else you need clear across the Pacific.

So again, I think the Japanese are going to be the ones who end up besieged.

American submarines can readily reach Hawaii from the West Coast plus there are the Line Islands to the South (reachable from CA AND Panama) as advanced bases for the fleet. Cutting off Japanese supply is within easy reach as early as mid 1942 even when the torpedoes work only somewhat.

After all the Allied submarines sank over a million tons in 1942 even with faulty torpedoes.
 
American submarines can readily reach Hawaii from the West Coast plus there are the Line Islands to the South (reachable from CA AND Panama) as advanced bases for the fleet. Cutting off Japanese supply is within easy reach as early as mid 1942 even when the torpedoes work only somewhat.

After all the Allied submarines sank over a million tons in 1942 even with faulty torpedoes.

The older S-Boats torpedoes that dated from WWI, worked well, other than running deeper than desired setting, and not having enough of them
 
Let’s say that the Japanese do take one of the outer islands for an airbase. Let’s even say there is an existing air field on the island. Now what do the Japanese do? They need at least some bombers, and fighters to protect the bombers when they are on a mission plus always have a CAP over the base. They need additional shipping to bring those in as well as their pilots, ground crews, ground control, administration, AA and crews, troops to defend the island and base. They need for house and feed those people, build hangers and since the islands have little in the way of supplies, the lumber and equipment to build those facilities need to be transported also. Maintenance equipment is also needed (the US might attack the base and you have to repair things).

If they have to build or extend an air base - more shipping needed.

So how many men will they have to support on the island? I have no background to estimate, but I’m sure there are others on this forum that can come up with a number and the amount of shipping to support a garrison of that size.

If they are actively attacking the Americans, they have to ship in more bombs, ammo, fuel. That means even more ongoing shipping.

Where will they find it and the extra fuel? Oil reserves take another hit.

Thank you,


MrBill
 
the Roads is vulnerable to submarine attack (and stopped being used as a major anchorage for the Pacific Fleet early in 1941 for that reason) and doesn't give you much of an island base.

Yes, that is what I was telling you when I said Pearl Harbor was superior because it was a 'protected anchorage'. Lahaina Roads was not. You had said,

there is only one major anchorage (Pearl Harbor)

Which is not the case; there were two major fleet anchorages, not one. As the Americans would have the one, the Japanese would presumably take the other and accept the loss of a few marus to submarines, sowing minefields to keep these intrusions down, (the USN rejected mine defenses in Lahaina because the currents would cause mines to break loose and float away, less of a concern in offensive wartime ops than peacetime defensive ops).

Lanai is a glorified pineapple plantation with a small airport (5000 ft runway now) which may or may not have been present then. Maui does have useful land area but again we run into the need to haul everything from Japan to construct a base. In World War II building advanced bases was not a Japanese strong suit, with Rabual being the rare exception.

Tough to get an exact figure on the outer islands capacity for airpower. Maybe around 100-150 aircraft and maybe another 60 seaplanes kind of thing. Insufficient against Oahu on its own, but if KB neutralizes Oahu's airpower it is sufficient. For the use of a base like on Maui, SOP was to haul it over the beach to the airfield via landing barge. Maui was perfect for that - well sheltered.

As to the blockade, it would rapidly be questionable as to who was blockading whom ... the oil requirements alone for routine voyages from Japan to Hawaii would be daunting.

Marshalls were closer so if investing Hawaii it would be necessary to use that as the advanced fleet base rather than Japan.

The Americans are awash in the stuff (in fact its handy as its extracted in California) while the Japanese have a very limited stockpile to fuel ALL operations that they must conduct in order to get the oil in the East Indies in order continue to function.

The NEI were functionally irrelevant to the outcome of a Japanese-American war. At best, if in Japan's possession they might be useful as a bargaining chip or to prolonging the agony. But in terms of the war Combined Fleet identified as the one it could win (1 year's duration), the NEI were a useless drain of combat resources.

An adult human eats about 2-3 pounds of food a day, setting aside packaging. That doesn't count literally everything else, from medical supplies to cloth to other basic requirements. While the Japanese may not care if the civilians starve (and clearly based on their World War II track record that is a low priority for them), they do care if their garrison starves.

There were about 82,000 head of cattle on the Big Island, for example. I think the IJA had rifles. There were about 12,000 cattle on Oahu and the US army also had rifles. OTOH, they also had about 350,000 people, so those 12,000 cattle won't go as far. In terms of the garrison, supply of it would be a major undertaking, maybe 20 ships or more per month for the first, maybe, half year. (Later, once population was reduced via evacuations to match food production, and stores were in place, Hawaii's garrison could function with much less monthly supply).

Plus you are talking about hauling aviation fuel, lubricating oil, spare parts, replacement airframes, ammunition, and literally everything else you need clear across the Pacific.

It was all about who had the airpower. If the US got it, the Japanese would be under siege and it would be a debacle. If the Japanese kept it, Oahu starts to starve.

American submarines can readily reach Hawaii from the West Coast plus there are the Line Islands to the South (reachable from CA AND Panama) as advanced bases for the fleet. Cutting off Japanese supply is within easy reach as early as mid 1942 even when the torpedoes work only somewhat.

Submarines in WW2 inflicted attrition but did not decide a single naval campaign.
 
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Let’s say that the Japanese do take one of the outer islands for an airbase. Let’s even say there is an existing air field on the island. Now what do the Japanese do?

The Japanese didn't build hangers AFAIK.

The immediate objective would be to establish a seaplane base or two to immediately support naval operations - finding the US carriers for KB to then attack. The same doctrine was attempted at Midway, (where Kure Island was slated for capture as a seaplane base on 5 June). The seaplane bases just established would cover preliminary landings for air bases, again, as per the SOP at Midway.

So how many men will they have to support on the island? I have no background to estimate, but I’m sure there are others on this forum that can come up with a number and the amount of shipping to support a garrison of that size.

For what, a siege or an invasion of Oahu? A siege, maybe 5,000-15,000 on the outer islands (depending on how many they take). An invasion - maybe 75,000 (plus 15,000 on the other islands = 90,000.)

Where will they find it and the extra fuel? Oil reserves take another hit.

Sounds like you did the math. Post your calculations please.
 
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