WI Japanese VII Uboats

Why were the allies not afraid of Japanese submarine and afraid of German submarines
The problem with turning Japanese submarines loose against the sea lanes was
Because the Japanese used their submarines as auxiliaries to the fleet, not as commerce raiders. It was the way they were used not the quality of the boats or crews that made the Uboats such a threat.
Because the Germans knew how to use their submarines
Barry has already said it but I think it's more than IJN simply doesn't have a target to cut off that can be vital like KM doing so to GB mainland? Cutting of PI was already done by surface fleet, and they can't cut the continental US.... a sub campaign against US simply can't be decisive and Japan needs a short war anyway.
 

Sargon

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Japan had some decent boats, but the large cruiser types were slower divers and less manoeuvrable underwater. Whilst German designs might point to better depth capabilities the problem, as others here have noted, is the doctrine of their use. Even with their existing subs, they could have caused more trouble in terms of hitting supply lines, yet they didn't. It wouldn't actually change much.


Sargon
 
Japan had some decent boats, but the large cruiser types were slower divers and less manoeuvrable underwater. Whilst German designs might point to better depth capabilities the problem, as others here have noted, is the doctrine of their use. Even with their existing subs, they could have caused more trouble in terms of hitting supply lines, yet they didn't. It wouldn't actually change much.
Sargon
The problem was that IJN subs, especially the big Junsen types, were no good for commerce raiding. They were just too big. To attack a sub needs to be invisible, like the smaller type VIIs and even IXs at night (before radar). New Junsens couldn't effectively hunt on the surface and had to rely on submerged attacks. Aware of these issues, and seeking to increase the effectiveness of their ally, in 1943-44 the Germans sent a couple of IXs for the Japanese to copy.
Type VII boats were well suited for commerce raiding or anti convoy operations but had too limited endurance for the Pacific. Type IXs combined better endurance with small enough size so they were considered better for Japan's needs.
 

Sargon

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The problem was that IJN subs, especially the big Junsen types, were no good for commerce raiding. They were just too big. To attack a sub needs to be invisible, like the smaller type VIIs and even IXs at night (before radar). New Junsens couldn't effectively hunt on the surface and had to rely on submerged attacks. Aware of these issues, and seeking to increase the effectiveness of their ally, in 1943-44 the Germans sent a couple of IXs for the Japanese to copy.
Type VII boats were well suited for commerce raiding or anti convoy operations but had too limited endurance for the Pacific. Type IXs combined better endurance with small enough size so they were considered better for Japan's needs.
They weren't good for commerce raiding, but they could have still done more than they did, which was hardly anything in terms of hitting supply lines. Less useful attacks with boats that are not great for the task are better than hardly any. We can give Japan a good number of German U-Boats and combine long range with as many of those as we like. Unless the IJN radically change the doctrine they had, there is not going to be much useful change. Historically, the IJN was slow to adapt to matters. It only belatedly realised more needed to be done for escorting merchant marine for example.

And any change that somehow manages to happen is going to be too late.


Sargon
 
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What if the Japanese goverment in 1930s build 20+ VII Uboats under license from Germany and have a German military mission train the crews(let's say the Japanese navy see the potential of German Uboats)?how much effect woul Japanese navy having 20+ VII Uboats have on the early years of the pacific war ww2?
Type VII was designed originally as a fast to construct cheap medium ranged, (Northsea & Atlantic) boat, adequate for operations in the North Atlantic and only with supporting replenishment vessels, or bases near the operational area capable of patrolling and attacking effectively against Allied supply routes. The Pacific theater was vastly larger and the Type VII completely incapable of operating effectively in this area, no matter what you wanted of them to do. Since the Allies faced a IJN with a totally different submarine doctrine compared to the Germans, the Japanese submarines were very long ranged in general and quite capable boats as such, but deployed in a very insufficient way, not against the transportlines, but mostly as patrolboats to interdict enemy warships most of the time. (a rather ineffective way to use submarines of this timeframe to start with, until the arival of nuclear attack submarines after the war)
 
The Type VII was too late to serve as a POD and optimised for Atlantic operations.
A better POD would be for the IJN to get a late war Type U-93 submarine as war reparation in 1919, as well as one of the unbuilt "Project 43" (U-115 and U-158 classes) submarines. The later boats combined (on paper, none were finished) excelent range with fast diving and agility. Working from this (project 43) they could have built a single balanced design optimised for their needs, rather than the multitude of different classes they used OTL.
OTL they got U-125, a cruiser/mine layer and U-51, a mid war medium submarine.
 
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The criticism of the Japanese for not using their boats for commerce raiding is bad logic. A war on commerce is a strangulation war and those take a lot of time and a long war is the war Japan had a zero percent chance of winning. Whatever minimal gnat's ass chance the Japanese had at winning was a short war that the Allies decided wasn't worth fighting. The best employment of Japan's submarines in that type of war is going after high value assets like aircraft carriers and battleships as a way of winnowing down Allied capabilities in the near term and increasing the prospects of a Japanese victories early in the war while decreasing the ability of the Allies to respond. In other words, for the only type of war Japan had any hope of winning (however small that hope may have been), their submarines were employed properly.
 
The criticism of the Japanese for not using their boats for commerce raiding is bad logic. A war on commerce is a strangulation war and those take a lot of time and a long war is the war Japan had a zero percent chance of winning. Whatever minimal gnat's ass chance the Japanese had at winning was a short war that the Allies decided wasn't worth fighting. The best employment of Japan's submarines in that type of war is going after high value assets like aircraft carriers and battleships as a way of winnowing down Allied capabilities in the near term and increasing the prospects of a Japanese victories early in the war while decreasing the ability of the Allies to respond. In other words, for the only type of war Japan had any hope of winning (however small that hope may have been), their submarines were employed properly.
And that exposes a contradiction btw IJN war doctrine and war practice. Having built their fleet for an extended decisive battle that included an attrition phase in which the USN fighting power would be degraded by submarines, longe range aircraft, carrier based aircraft and large scale night torpedo attacks before a final decisive blow to be delt by the battleships, which would require the USN to be on the offensive, they then started the war with a (partial) decapitation strike that forced the USN to fight a defensive war.
In other words, the IJN war strategy (surprise strike followed by offensive) was the oposite of their forces building strategy (in depth defence).
Its as if a tennis player had spent all his training perfecting his back of the court game only to decide to play his game at the net at the last minute.
 

Sargon

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Actually, it wasn't as if some in the IJN weren't aware of the issues. The problem is the doctrine adopted by the navy came from Satō Tetsutarō through his writings where he emphasised command of the sea which lead to the IJN's Decisive Battle strategy. Sato's theories stemmed in part from his observation in the Anglo-Dutch War in which he criticised the Dutch for in his view being too pre-occupied with their defence of maritime trade and praised the English for their concentration on command of the sea, thus attributing it in this case the reason for the English victory. He noted the Dutch had a smaller Navy and because of having less assets and seeking to protect merchant vessels lost its ability for free manoeuver. He blamed their defeat upon this and laid out his thinking in The Summarized Theory of A History of National Defence published in 1911. Mixed in with Mahanian theory, the IJN later adopted measures of his ideas into their doctrine with the focus of the destruction of the opposing fleet being necessary to secure command of the seas and thus protecting trade.

Some officers in the navy had observed the successes of Germany's U-Boat fleet during World War I and were aware of the vulnerability of Japan in this regard, but this did not significantly alter the doctrine, which was also hampered by thoughts at the time they would not get enough funding for submarines anyway. In addition to this, many of the reports sent back by IJN officers observing the naval war in Europe during World War I concentrated on surface actions and not so much on submarine actions. Still, in some of the later Taishō and early Shōwa eras Naval Annual Operational Plans, there was some thought put into engaging SLOCs off the US west coast with some submarine forces keeping the bulk of them back for the Decisive Battle, illustrating some awareness of potential usage. However, the problem was they did not note that command of the sea could be lost by various means, and believed it could only be lost by not winning a decisive battle, plus did not allow for the recognition of the ability of submarines to degrade that ability via attacks on SLOCs (ironic considering some of the thoughts in the Operational Plans).

Even as a result of naval exercises carried out from 1937 until into the war itself, naval commanders had reported back the potential for success using existing submarines against SLOCs prior to the Decisive Battle, but the results of these exercises and operational experience of submarine commanders were not adopted into doctrine. Thus according to submarine commanders themselves, some of the subs were capable of SLOC usage and could be effectively employed in that role, but it is also true because of the Decisive Battle doctrine, the larger submarines were not really suitable for such. The IJN's submarine arm did achieve some notable attacks (the one by I-19 against USS Wasp, USS North Carolina and USS O'Brien was truly spectacular in its success for example), but its employment was criticised by some in the Japanese navy itself and the overall results of it even in its warship focused attack role were acknowledged as disappointing by IJN officers themselves. Not that this would have helped that much, as once started in the way it was, the war with the US was going to be lost anyway, even if various senior naval commanders could not see or accept this. A quick decisive war, though planned for was not certain and some in the IJN were very aware of this but overconfidence and an assumption the enemy would follow IJN anticipated moves failed to account for the more unpredictable nature of war and the opponent not doing what you expect. The focus remained on the Decisive Battle approach until it was far too late to even have that battle.

The thing is naval strategy has to take into account multiple factors and not rely on only one aspect of doctrine over another but incorporate several together. However, that of course is dependent upon planning, budgets, shipbuilding and industrial capacity as well as looking at aspects of doctrine.

There's a good essay about this in Ito Masanori's book, The End of the Imperial Japanese Navy where he describes his interviews with naval officers about the employment of Japan's submarine fleet, the shortcomings in doctrine and their acknowledgement of errors and the disappointment overall operational usage caused. As an aside, it's also fascinating as it has a very rare interview with Vice Admiral Kurita about his actions at Leyte Gulf where it explains some of his thoughts about moves he made there. The book also notes the idea of the Decisive Battle held sway even at this late stage of the war.

It can be quite revealing sometimes reading Japanese sources and documents.


Sargon
 
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Barry has already said it but I think it's more than IJN simply doesn't have a target to cut off that can be vital like KM doing so to GB mainland? Cutting of PI was already done by surface fleet, and they can't cut the continental US.... a sub campaign against US simply can't be decisive and Japan needs a short war anyway.
The United States had a long supply chain coming from the Continental US across the Pacific. Disrupting that would have slowed the Americans down and hampered their combat capability
 
The United States had a long supply chain coming from the Continental US across the Pacific. Disrupting that would have slowed the Americans down and hampered their combat capability
And the Allies will adjust and provide escorts (something they were already doing) and the Japanese will create problems but ultimately they will be unable to stop the Allies from doing what they needed to do. The Germans with far more submarines in a far smaller ocean could not prevent the Allies from doing what they needed to do. And again, a war against SLOCs is a long term campaign which is precisely what the Japanese cannot afford. Their only hope (and hope is the appropriate word here) was a quick victory in a quick war.
 
Actually, it wasn't as if some in the IJN weren't aware of the issues. The problem is the doctrine adopted by the navy came from Satō Tetsutarō through his writings where he emphasised command of the sea which lead to the IJN's Decisive Battle strategy. Sato's theories stemmed in part from his observation in the Anglo-Dutch War in which he criticised the Dutch for in his view being too pre-occupied with their defence of maritime trade and praised the English for their concentration on command of the sea, thus attributing it in this case the reason for the English victory. He noted the Dutch had a smaller Navy and because of having less assets and seeking to protect merchant vessels lost its ability for free manoeuver. He blamed their defeat upon this and laid out his thinking in The Summarized Theory of A History of National Defence published in 1911. Mixed in with Mahanian theory, the IJN later adopted measures of his ideas into their doctrine with the focus of the destruction of the opposing fleet being necessary to secure command of the seas and thus protecting trade.

Some officers in the navy had observed the successes of Germany's U-Boat fleet during World War I and were aware of the vulnerability of Japan in this regard, but this did not significantly alter the doctrine, which was also hampered by thoughts at the time they would not get enough funding for submarines anyway. In addition to this, many of the reports sent back by IJN officers observing the naval war in Europe during World War I concentrated on surface actions and not so much on submarine actions. Still, in some of the later Taishō and early Shōwa eras Naval Annual Operational Plans, there was some thought put into engaging SLOCs off the US west coast with some submarine forces keeping the bulk of them back for the Decisive Battle, illustrating some awareness of potential usage. However, the problem was they did not note that command of the sea could be lost by various means, and believed it could only be lost by not winning a decisive battle, plus did not allow for the recognition of the ability of submarines to degrade that ability via attacks on SLOCs (ironic considering some of the thoughts in the Operational Plans).

Even as a result of naval exercises carried out from 1937 until into the war itself, naval commanders had reported back the potential for success using existing submarines against SLOCs prior to the Decisive Battle, but the results of these exercises and operational experience of submarine commanders were not adopted into doctrine. Thus according to submarine commanders themselves, some of the subs were capable of SLOC usage and could be effectively employed in that role, but it is also true because of the Decisive Battle doctrine, the larger submarines were not really suitable for such. The IJN's submarine arm did achieve some notable attacks (the one by I-19 against USS Wasp, USS North Carolina and USS O'Brien was truly spectacular in its success for example), but its employment was criticised by some in the Japanese navy itself and the overall results of it were acknowledged as disappointing by IJN officers themselves. Not that this would have helped that much, as once started in the way it was, the war with the US was going to be lost anyway, even if various senior naval commanders could not see or accept this. The focus remained on the Decisive Battle approach until it was far too late to even have that battle.

The thing is naval strategy has to take into account multiple factors and not rely on only one aspect of doctrine over another but incorporate several together. However, that of course is dependent upon planning, budgets, shipbuilding and industrial capacity as well as looking at aspects of doctrine.

There's a good essay about this in Ito Masanori's book, The End of the Imperial Japanese Navy where he describes his interviews with naval officers about the employment of Japan's submarine fleet, the shortcomings in doctrine and their acknowledgement of errors and the disappointment overall operational usage caused. As an aside, it's also fascinating as it has a very rare interview with Vice Admiral Kurita about his actions at Leyte Gulf where it explains some of his thoughts about moves he made there. The book also notes the idea of the Decisive Battle held sway even at this late stage of the war.

It can be quite revealing sometimes reading Japanese sources and documents.


Sargon
It's easy to criticize the decisive battle mind set but honestly it was their best shot. Win a decisive battle or a series of them early on and hope (yes hope) the Allies decide the western Pacific isn't worth fighting for.
 

Sargon

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It's easy to criticize the decisive battle mind set but honestly it was their best shot. Win a decisive battle or a series of them early on and hope (yes hope) the Allies decide the western Pacific isn't worth fighting for.
Their best shot was not going to war in the manner they did in the first place. As my research when living and working in Japan showed me, there were officers in the IJN who were far from stupid and knew a quick war was not certain, and were indeed mindful of possible US reactions to moves they could make. Some were not happy at all at the prospect of going to war with the US as they knew they would lose and why they would lose. However, most of the leadership did not wish to hear of such defeatist talk. Large parts of the IJN doctrine worked on the assumption the opposing force would follow what they predicted for it, so it was flawed from the start. Warnings were ignored over a long time, when there could have been an opportunity to address various deficiencies in the fleet that were known about well before the war even started.

Going to war, you need the best plans available and to be able to listen to various ideas put forward. This was a failure of listening to warnings and learning exercises that did not match up with their biases. If it contradicted their assumptions, it was dismissed, and this is prewar stuff. We all know the examples of Midway wargaming when Nagumo's carriers suffered losses, and these being dismissed as well, but this was a characteristic which was entrenched and existed before the war, and it was a dangerous one.

If it was just about after the war as in OTL, then you have a point their best shot was a short and decisive war, that was indeed their only hope and what they were aiming for. I get what you are saying, yes, it is indeed easy to criticise and we do have hindsight. Trouble is it's still easy because they could have done something about it much earlier due to awareness of the flaws in the doctrine, and various IJN officers found it easy enough to criticise it themselves, but hard to get listened to. However, once again they didn't use their submarine fleet even in its intended role efficiently and properly. The fact they had been warned a number of times by officers and analysis in their own exercises what could be a real danger and then dismissed it because it wasn't convenient is the real issue.

Back to the question about German U-Boats, we can see that even if they get them, there's not going to be much change in the outcome, even if they do somehow alter their doctrine and use them to attack SLOCs as was shown as at least somewhat feasible by reports from their own submarine commanders. It would be too little, too late. The worst that happens for the US is somewhat of a slowdown in the their advance, but it won't delay matters by a large margin.

However, if people desire more results than OTL, then at least their submarine force would have something more to show for it, even if it winds up not that much, and that's the point that's trying to be got at and seems to be what the topic of this thread is asking about. But we don't just need a POD well back in the 30s, doctrinal change is required as well if more than that is desired. And if they can manage to listen and change one part of doctrine, well, it may not be impossible other elements may perhaps change too. It's quite an ask though.

People can have deep disappointment in the submarine arm's performance (as happened) or a little less disappointment about how it was used. It's not like the focus of attacking warships actually did that much to change the outcome for Japan, apart from a few notable successes. Even the employment of the submarine role in the doctrine that was expected of it largely failed.

Phew. Doing too much writing today. That's not normal. I think I'll relax with some more Ken Boon telly stuff. :)


Sargon
 
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The trouble is that didn’t until late in the war.
Can you please explain what you mean? I think you may not understand what slant ranging and range gating by doppler is as opposed to a depth guess of the sub based on simple bearing angle solution of the signal return.

IOW if your acquisition thresh signal hold is 2000 meters and your angle solution on the bearing is 5 degrees, you trig out a depth guess of 175 meters at your floor estimate of where the sub and as you make your attack run you set your patterns to explode at 50, 75, 100, 125 and 150 meters as the destroyer(s) make the overrun.
 
Can you please explain what you mean? I think you may not understand what slant ranging and range gating by doppler is as opposed to a depth guess of the sub based on simple bearing angle solution of the signal return.

IOW if your acquisition thresh signal hold is 2000 meters and your angle solution on the bearing is 5 degrees, you trig out a depth guess of 175 meters at your floor estimate of where the sub and as you make your attack run you set your patterns to explode at 50, 75, 100, 125 and 150 meters as the destroyer(s) make the overrun.
The trig solution you quote is only one point.
You have no idea where the sub is in the sample box.(actually a tube). The box is 3D. The pulse length has a range error. The sub can be anywhere in the beam; the sides or bottom before losing contact. Now tell me the depth, plus or minus at 2000m.

The kill radius of a 300lb depth charge is 4-9m.

Even with infinite DC, and 5 runs, you can only bomb one space at one setting at one time. Or dilute your attack.

This is not video game (50, 75 etc) and you need to pick ONE!
 
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