A Japanese invasion of Hawaii

[Curtis Lemay]

So does that mean both KB and the APDs have to be together 200nm from the islands at what I assume is early in the night of Dec 6th? If so, does that mean the entire force has made most of its approach to this position pretty much all in daylight?

Your own figures were 33 hours at top speed. That would be a range of over 1400 miles. Now, I'm not saying they should spend a full 33 hours at top speed, but they would have had lots of slack to top off soon enough to out-distance the main fleet in order to be in position to make the final run to the islands entirely at night.

Your range calculation seems a bit off but I've gotta admire your optimism overall. These top-end fuel consumption figures are normally based on a short speed trial (1-2 hours) in good conditions when the ship was just out of the shop. Now change the sea state to moderate/heavy, add the wear and tear of weeks in the Northern Pacific, extend the speed run out to 8-12 hours and then put that single ship in a 12 ship formation at night that has to operate together in unfriendly waters. Consider what impact that has now had on fuel consumption at all speeds and also on the chances of being able to operate at that top speed mentioned in the sales brochure.

During the Guadalcanal campaign when the Tokyo Express destroyers were running the most dangerous part of The Slot in daylight, the formation speeds were still generally kept in the 25-30 knot range. After nightfall, it would drop to 20-25 knots even though they were still in dangerous waters. These guys were conducting missions similar to that of your imagined force. I'd suggest you might want to follow the real life experts in deciding what speeds were practical for your scenario.

It would still be interesting to find out from you where everyone is supposed to start the day before the attack in terms of distances from the Hawaiian Islands as this destroyer mission set up so far is making little sense in terms of timing.

As I said, plenty of slack in that 1400 mile figure.

[Curtis Lemay]

Only the Luzon invasion is being canceled. The rest of the PI operation still takes place.

warspite1

Not so. You've said you are taking aircraft from the PI operation. You see this is why detail is important. At the moment all you are doing is changing your answers to suit your argument, and you can do this because you never trouble yourself with detail.

They would then be replaced with others. I've said that reduction of the air assets on Luzon may take longer than historical. It still gets done. The rest of the PI operation still takes place and puts Luzon far in the Japanese rear. So...no ahistorical rescue TF.

[Curtis Lemay]

There are eight capitol ships. They have huge fuel stocks - far in excess of DDs. Topping off the DDs would be insignificant to the big guys. And, after the raid, they will all soon be refueled on the way back.

warspite1

But you don't know this. You don't know how many destroyers it would have taken to land your four battalions - let alone the vast amounts of supplies needed by the air units. You say you've wargamed this and yet you can't say what destroyers numbers are required - indeed you now say the Japanese would need destroyer conversions which they didn't have.

'Huge fuel stocks'....seriously? You have the KB (plus goodness knows how many destroyers) sailing for the attack on Pearl. In your scenario though the KB have sailed with the knowledge that they may not make the attack straightaway because they don't know when the carriers will be in port. So they need to be prepared for tooling around in the North Pacific for an indeterminate length of time. Apart from the obvious problems that you've ignored, there is the problem of fuel replenishment.

Based on the known and expected (though not certain) carrier movements, the enlarged KB will have been at sea for over two weeks (it may have been more). The ships would have been burning oil and supplies and sailing from the refuellling point to the flying off point and back again. How long would it take to transfer oil to the destroyer flotillas (assuming one flotilla per island)?

You refuse to provide detail you refuse to provide a timeline. Of course your 'plan' works when you don't have to evidence it.

The TF had enough fuel to get far away from Pearl to be refueled. That refueling point just moves a bit further East. Ships refuel on the move. They don't have to stop to refuel.

[Curtis Lemay]

Essentially you are saying that the Japanese completely and utterly wasted their time in employing the Northern Pacific route.

Good grief. Can the entire fleet traverse the entire central pacific in one night? Of course not. But the DDs can traverse about 500 miles in the night before the raid.

warspite1

Again you are changing your argument to suit each question. One of the biggest reasons the Japanese would never have considered this ridiculous plan is that secrecy was vital. They were not going to swan around in the North Pacific for an unknown length of time in the hope of getting the carriers. Why? because they couldn't afford to be detected. But your answer to this was that even if they were detected it wouldn't matter because they would say they were on a training exercise. A training excerise a few hundred miles from the HI????

So if there is no problem with detection, why sail the treacherous Northern Pacific route and be prepared to sink any vessels they come into contact with? Was detection a problem for the KB or not? Please stick to one answer.

Most of the time in the North Pacific it will be heavy seas and storms. When it isn't, the carriers will have scout planes out to enable them to avoid any ships in their paths. It will be very hard to detect them. Only if they encounter the US Carriers will there be a real risk of detection. And then what would they have done, historically? Here's just another reason why it's so beneficial to have the option to abort. And they aren't going to get a few hundred miles from Pearl without the green light.

[RangerJoe]

There was no operation in the current SRA invasion plans that specifically needed the unique capabilities of APDs for its execution. Even the Wake Invasion didn't rely solely on them. So why would the Japanese have seen any pressing need for more APDs at this point, especially since the conversion would come at a cost to other capabilities.

For the operation I'm adding. Yamamoto knows about that and its needs. But he can justify APD conversion to his superiors just in general. APDs are useful things to have.

And then there would be the issue of finding the spare yard space for the conversion of what sounds like a considerable number of destroyers. The Japanese naval and civilian shipyards were already working at full capacity right up to the start of the war, following the schedule that had been laid out in detail the previous financial year. It's not really a situation favourable to Yamamoto being able to just slip a couple of changes past the relavent authorities.

Not building APDs from scratch. Just modifying the superstructure of existing DDs. No slipways or dry docks needed. Just dock space.

Japan did not need APDs, they needed more fully capable destroyers.

Besides, there were no excess destroyers available to be used for this. But there were other ships that could have been used and much more successfully. If they would have been seen, it would have been a "So what?" response.

[Buckrock]

Not building APDs from scratch. Just modifying the superstructure of existing DDs. No slipways or dry docks needed. Just dock space.

You misunderstand. All work of this nature was conducted at either the Navy Yards or at a few of the larger commercial shipyards. As were the refits, overhauls, modifications, etc of IJN warships that were currently being rushed through in anticipation of war. That is what your conversion work would be competing with for space at the yards. They were not just used for new construction.

As I said, plenty of slack in that 1400 mile figure.

But somewhat meaningless without the context of the ship movement details of the 24 hours prior to the raid. When I made a guestimate based on your vague description of the destroyer operating parameters for the mission, it looked unachievable by any WWII standards I'd seen. Perhaps if you lay out the distances and relative positions at key times for KB and for the APDs during that 24 hour period, maybe I can see the error of my ways.

[Curtis Lemay]

Here is the link to an APD I provided a while back:

https://destroyerhistory.org/de/apd/

Note that it has 1400 tons displacement. It carries 162 officers and men with 8 trucks and 4 howitzers. It has 10,500 cubic feet of various cargo space (6000 ammo; 3500 cargo; 1000 gasoline). Not sure how that translates into weight, but if it were all gasoline it would total 245 tons (I expect ammo to be denser than gas, but cargo less dense). But its speed was only 23.7 knots.

It has an armament of 1 5" gun, 3 dual 40mm, 6 20mm and 2 depth charge tracks. Before conversion, it had 3 3" guns, 1 1.1" quad gun, and 8 20mm guns. It had 8 K-gun depth charge projectors and a Hedgehog ASW mortar, along with the 2 depth charge tracks.

So, it lost two main gun turrets, the 1.1 quad turret, and two 20mm guns. Plus the torpedo tube, Hedgehog, and K-guns. No change to propulsion. Added the 3 40mms.

Here is the link to the Mitzuki-class destroyers that were used for APDs in the war:

https://en.wikipedia.org/wiki/Mutsuki-class_destroyer

Note its displacement is 1445 tons. So...about the same as the example APD.

It has 4 120mm guns, 2 7.7mm guns, 2 triple torpedo tubes. It carries 12 torpedos, 18 depth charges, and 16 naval mines.

So...get rid of 3 120mm gun turrets, and the 2 triple torpedo tubes. Dump the trucks, howitzers, torpedos and mines. That has to be at least equal to what the example APD lost - in weight. But, I'll trade supply weight for troop capacity.

So...Let's say the new APD Mutsuki will have 200 tons cargo and 200 troops. Speed remains at 37knots.

The 12 Mutsuki's can then haul the two Jap battalions (2400 men) and 2400 tons of supplies and equipment.

At this point, I'll cut back the invasion to just Maui. It's the only manatory part of the invasion, initially.

[Curtis Lemay]

Not building APDs from scratch. Just modifying the superstructure of existing DDs. No slipways or dry docks needed. Just dock space.

You misunderstand. All work of this nature was conducted at either the Navy Yards or at a few of the larger commercial shipyards. As were the refits, overhauls, modifications, etc of IJN warships that were currently being rushed through in anticipation of war. That is what your conversion work would be competing with for space at the yards. They were not just used for new construction.

No. I'm not misunderstanding. All it needs is dock space (with cranes, of course). It doesn't require any special facilities.

[Curtis Lemay]

Besides, there were no excess destroyers available to be used for this.

The Luzon invasion is postponed. That frees up lots of naval assets to be repurposed.

[Curtis Lemay]

Not building APDs from scratch. Just modifying the superstructure of existing DDs. No slipways or dry docks needed. Just dock space.

You misunderstand. All work of this nature was conducted at either the Navy Yards or at a few of the larger commercial shipyards. As were the refits, overhauls, modifications, etc of IJN warships that were currently being rushed through in anticipation of war. That is what your conversion work would be competing with for space at the yards. They were not just used for new construction.

No. I'm not misunderstanding. All it needs is dock space (with cranes, of course). It doesn't require any special facilities. And I've got at least 1000 miles of slack in the race to the islands.

[Buckrock]

Not building APDs from scratch. Just modifying the superstructure of existing DDs. No slipways or dry docks needed. Just dock space.

You misunderstand. All work of this nature was conducted at either the Navy Yards or at a few of the larger commercial shipyards. As were the refits, overhauls, modifications, etc of IJN warships that were currently being rushed through in anticipation of war. That is what your conversion work would be competing with for space at the yards. They were not just used for new construction.

No. I'm not misunderstanding. All it needs is dock space (with cranes, of course). It doesn't require any special facilities.

Dock space with cranes for conversion work on a Japanese warship in 1941 still meant either one of the five Naval Yards (ie Sasebo Naval Yard) or one of the larger civilian yards. Which is also where the IJN warships were being sent for the other "non-construction" work I mentioned earlier.

Hope that clears things up.

[Curtis Lemay]

You misunderstand. All work of this nature was conducted at either the Navy Yards or at a few of the larger commercial shipyards. As were the refits, overhauls, modifications, etc of IJN warships that were currently being rushed through in anticipation of war. That is what your conversion work would be competing with for space at the yards. They were not just used for new construction.

No. I'm not misunderstanding. All it needs is dock space (with cranes, of course). It doesn't require any special facilities.

Dock space with cranes for conversion work on a Japanese warship in 1941 still meant either one of the five Naval Yards (ie Sasebo Naval Yard) or one of the larger civilian yards. Which is also where the IJN warships were being sent for the other "non-construction" work I mentioned earlier.

Hope that clears things up.

Any place with dock and cranes would work.

[Buckrock]

Here is the link to an APD I provided a while back:

https://destroyerhistory.org/de/apd/

Note that it has 1400 tons displacement. It carries 162 officers and men with 8 trucks and 4 howitzers. It has 10,500 cubic feet of various cargo space (6000 ammo; 3500 cargo; 1000 gasoline). Not sure how that translates into weight, but if it were all gasoline it would total 245 tons (I expect ammo to be denser than gas, but cargo less dense). But its speed was only 23.7 knots.

It has an armament of 1 5" gun, 3 dual 40mm, 6 20mm and 2 depth charge tracks. Before conversion, it had 3 3" guns, 1 1.1" quad gun, and 8 20mm guns. It had 8 K-gun depth charge projectors and a Hedgehog ASW mortar, along with the 2 depth charge tracks.

So, it lost two main gun turrets, the 1.1 quad turret, and two 20mm guns. Plus the torpedo tube, Hedgehog, and K-guns. No change to propulsion. Added the 3 40mms.

Here is the link to the Mitzuki-class destroyers that were used for APDs in the war:

https://en.wikipedia.org/wiki/Mutsuki-class_destroyer

Note its displacement is 1445 tons. So...about the same as the example APD.

It has 4 120mm guns, 2 7.7mm guns, 2 triple torpedo tubes. It carries 12 torpedos, 18 depth charges, and 16 naval mines.

So...get rid of 3 120mm gun turrets, and the 2 triple torpedo tubes. Dump the trucks, howitzers, torpedos and mines. That has to be at least equal to what the example APD lost - in weight. But, I'll trade supply weight for troop capacity.

So...Let's say the new APD Mutsuki will have 200 tons cargo and 200 troops. Speed remains at 37knots.

The 12 Mutsuki's can then haul the two Jap battalions (2400 men) and 2400 tons of supplies and equipment.

At this point, I'll cut back the invasion to just Maui. It's the only manatory part of the invasion, initially.

I'd rather not play the imaginary changes to ships game. I know what the actual Mutsuki "conversion" was. It was not something the Japanese would have just decided one day would be a great addition to the class capabilities. It first took an unfavorable change in the fortunes of war during 1942.

IMO, something like the historical Mutsuki conversion wouldn't fix your problem but if you need it for your scenario you should be aware that the 37 knot speed is only the original destroyer design speed. I've seen several sources (Mark Stille's "Imperial Japanese Navy" being one) stating this class failed to reach that design speed and could only make 33 knots when built in the 1920's.

And then it got old. Which is probably why I've not seen mention of them doing more than 30 knots in Japanese accounts from the Solomons campaign.

[Buckrock]

No. I'm not misunderstanding. All it needs is dock space (with cranes, of course). It doesn't require any special facilities.

Dock space with cranes for conversion work on a Japanese warship in 1941 still meant either one of the five Naval Yards (ie Sasebo Naval Yard) or one of the larger civilian yards. Which is also where the IJN warships were being sent for the other "non-construction" work I mentioned earlier.

Hope that clears things up.

Any place with dock and cranes would work.

I wonder why the IJN never thought of that.

[Orm]

No. I'm not misunderstanding. All it needs is dock space (with cranes, of course). It doesn't require any special facilities.

Dock space with cranes for conversion work on a Japanese warship in 1941 still meant either one of the five Naval Yards (ie Sasebo Naval Yard) or one of the larger civilian yards. Which is also where the IJN warships were being sent for the other "non-construction" work I mentioned earlier.

Hope that clears things up.

Any place with dock and cranes would work.

This conversion would surely be picked up by US. I wonder what their analysis of such conversations would have been.

[warspite1]

Dock space with cranes for conversion work on a Japanese warship in 1941 still meant either one of the five Naval Yards (ie Sasebo Naval Yard) or one of the larger civilian yards. Which is also where the IJN warships were being sent for the other "non-construction" work I mentioned earlier.

Hope that clears things up.

Any place with dock and cranes would work.

I wonder why the IJN never thought of that.

warspite1

Well maybe one of many reasons is that for some reason there isn’t a plethora of ‘spaces’ that take ships of destroyer size and happen to have the required heavy duty cranes that could cope with this type of work.... oh and that have the required skilled work force at a time when the naval and civilian yards are massively in demand.... oh and this assumes the resources are available at a time when the IJN has numerous more important projects upon which to divide its finite resources.

[warspite1]

And they aren't going to get a few hundred miles from Pearl without the green light.

warspite1

But the KB needs to be in place before the green light. What is the point of being days from the flying off point when the news is received that the carriers are in port. The carriers could then sail while the KB are positioning.

[Buckrock]

Any place with dock and cranes would work.

I wonder why the IJN never thought of that.

warspite1

Well maybe one of many reasons is that for some reason there isn’t a plethora of ‘spaces’ that take ships of destroyer size and happen to have the required heavy duty cranes that could cope with this type of work.... oh and that have the required skilled work force at a time when the naval and civilian yards are massively in demand.... oh and this assumes the resources are available at a time when the IJN has numerous more important projects upon which to divide its finite resources.

It' seems pretty clear now that when Curtis Lemay stated the discussion was about what the Japanese could have done with his plan, he actually meant what they could have done if they weren't the historical Japanese with all their limited resources, annoying administrative systems, rigid command hierarchies, restrictive operational practices and a limited understanding of their own warship potential.

[Buckrock]

And they aren't going to get a few hundred miles from Pearl without the green light.

warspite1

But the KB needs to be in place before the green light. What is the point of being days from the flying off point when the news is received that the carriers are in port. The carriers could then sail while the KB are positioning.

One day we may find out just exactly how far from the Hawaiian Islands everyone is when that dang green light finally goes off.

[warspite1]

It' seems pretty clear now that when Curtus Lemay stated the discussion was about what the Japanese could have done with his plan, he actually meant what they could have done if they weren't the historical Japanese with all their limited resources, annoying administrative systems, rigid command hierachies, restrictive operational practices and a limited understanding of their own warship potential.

warspite1

Yep, same MO as the Spain thread. There is no point having a what if discussion if you don’t allow some liberties to be taken compared with what happened historically. But this - like Spain - goes beyond that to absurd lengths. An interesting discussion on what could perhaps have happened, just becomes fantastical nonsense whereby anything goes.