Japanese ASW

HJ Tulp

Donor
It might be an idea to look at the Italian actions against RN subs in the Med, as an idea what might have happened?

Not dissimilar; lots of shallow water, subs operating inshore a lot, 2nd rate (but not negligible) A/S force, aggressive sub skippers. Although the IJN wouldn't have the advantage of air cover.

Hmmm good idea. Do you know if the Italians used heavily protected, large convoys or smaller ones?

Riain said:
The IJN won't have to sink an Oboat, merely attack it and force it down while the convoy zags away out of range of the much slower Oboat with its very short range weapons. The real havoc with subs comes from pack tactics, the Uboats were famous for it and the USN worked in smaller packs of about 3 boats where the convoy would be boxed in and subject to multiple torpedo salvos from multiple boats. If you can vector multiple subs in on an invasion convoy then you stand a good change of sinking multiple ships and doing some serious damage, but a single boat will only get one or maybe two salvos off before the counter-attack and the convoy going out of range. One or two salvos isn't going to stop an invasion convoy and gathering enough subs onto a target will be difficult.

I agree with you. Luckily so did the Royal Netherlands Navy! The submarine arm was able to operate in divisions of 5 boats each. According to the source I mentioned in the OP they were also able to spot a enemy flotilla, steal a march on it during the night and then wait for them for an ambush. I'm a bit sceptical about the last claim though the speed of the Dutch submarines (roughly 18 knots) should be fast enough in theory.

What I am really curious about is the SOP of a japanese invasion fleet when attacked from beneath the water by multiple submarines. I assume that the destroyers will try to find and destroy or at least supress the submarines. How many destroyers though? And I assume the invasion fleet itself will keep steaming ahead as fast as possible. That means that part of the escort will be very much out of position if a second division or the ABDA-fleet makes a move.
 
Speed

The subs problem is it has to detect and intercept in order to attack.

Basically the faster the target the less likely the chance of getting into a firing position. The IJN found that problem in their sub fleet vs warship targets pre war and the RN reckoned ( from memory) that a convoy with a sustained speed of 12kts + was uninterceptable except by luck, the target runs into the subs range.

Trade war is very different from attacking an invasion convoy. The invasion convoy can be expected to be fast and not to hang around after it has unloaded.

Basing a defence on subs requires a lot of warning and precise intelligence on the destination or the sort or a helluva lot of subs.
 

HJ Tulp

Donor
The subs problem is it has to detect and intercept in order to attack.

Basically the faster the target the less likely the chance of getting into a firing position. The IJN found that problem in their sub fleet vs warship targets pre war and the RN reckoned ( from memory) that a convoy with a sustained speed of 12kts + was uninterceptable except by luck, the target runs into the subs range.

Trade war is very different from attacking an invasion convoy. The invasion convoy can be expected to be fast and not to hang around after it has unloaded.

Basing a defence on subs requires a lot of warning and precise intelligence on the destination or the sort or a helluva lot of subs.

Which is why the RNN invested heavily in air-to-sea reconnaissance and excellent communications between submarines, planes and HQ and even planes and submarines. What also helps is the geographic dimensions of the Dutch East Indies: a lot of islands, narrow straits. OTL the RNN switched to a strategy of trying to defend the outer lying island even though they didn't have nearly enough equipment to do so. ATL they keep concentrated on Java and there are really only two ways for the Japanese to get there.
 
Which is why the RNN invested heavily in air-to-sea reconnaissance and excellent communications between submarines, planes and HQ and even planes and submarines. What also helps is the geographic dimensions of the Dutch East Indies: a lot of islands, narrow straits. OTL the RNN switched to a strategy of trying to defend the outer lying island even though they didn't have nearly enough equipment to do so. ATL they keep concentrated on Java and there are really only two ways for the Japanese to get there.

The Japanese would have had total air superiority. Historically the islands were being bombed while the Japanese landing forces were unloading; I'm not sure something like that would have worked. The Japanese also would (and did) attempt to destroy the submarines and their support facilities before they could move against the invasion shipping.

Even if the submarines could effectively sortie, again, I'm not sure they could have made a major impact. There might have been some successes here and there, but the speed and power of the Japanese offensive caught the ABDA forces totally off-guard: their best effort (Java Sea) was crushed with barely 24 hours' delay in the IJN schedule. They were pulverized before they even had a chance of properly collecting themselves. Even if losses in transports were higher than in OTL (historically the Japanese did lose a number of them to Allied subs, see http://www.dutcheastindies.webs.com/under_sea.html) it would have ultimately mattered little, especially given the disparity in power between the ABDA land forces and the IJA at the time. In my opinion the overall pace of operations would have been minimally affected by a better Allied sub fleet in the manner described here.
 

hipper

Banned
For an effective Dutch anti Japanese strategy have them "do a Poland" and concentrate on breaking Japanese Cyphers pre war.

With this information the Dutch submarines can always be in the right place to intercept high value ships and reach havoc against the substantial number of ships not in Convoy.

this was the OTL reason for the american successful submarine campaign. .

cheers Hipper.
 

HJ Tulp

Donor
For an effective Dutch anti Japanese strategy have them "do a Poland" and concentrate on breaking Japanese Cyphers pre war.

With this information the Dutch submarines can always be in the right place to intercept high value ships and reach havoc against the substantial number of ships not in Convoy.

this was the OTL reason for the american successful submarine campaign. .

cheers Hipper.

By then the Dutch East Indies will have been overrun though.
 
For the submarine oriented strategy to work you will need a lot more submarines. 15 subs (the OTL numbers) just won't get it done, especially since some of those submarines are around 20 years old.

Boats will get sunk and damaged, boats will be down for maintenance, and boats in port will be subjected to air attack.

Even if the Japanese are drinking lead paint (a favorite analogy on this forum) when it comes to ASW, they will still get lucky a few times and then add in basic attrition and the 15 boats will get worn down quickly. Just like they did OTL.
 
Japanese ASW in 1941-2 wasn't so much prosecute-to-kill as prosecute-to-drive off. Given how limited their depth charge supply was, it's understandable. Their biggest problem was giving up too early: there are several instances of USN sub skippers, their boats pinned down by IJN surface vessels, telling their men to prepare to destroy classified materials, and get ready to battle-surface and fight it out, when the surface ships gave up and left.

It wasn't until destroyers had wartime refits that depth charge capacity was increased, from 36 on average to 72. The Matsu-class DEs only had 36, though. Their escorts had up to 120 DCs.
 

HJ Tulp

Donor
wether you think the ATL Dutch strategy has worked (I'm not convinced myself really) I think it would still be interesting to see what this leads to.
Don't worry, you guys may still rip me to shreds once I actually start writing the TL ;)

Until then I need some information regarding Japanese escort doctrine in 1941 (as I'm sure it's doctrine changed during the course of the war).

Let me sketch a sandbox scenario. Do note that I'm not asking about the plausibility of the scenario itself but only want to know what the IJN response would be.

The scenario:

1. A Japanese invasionfleet consisting of around 50 troopships and 12 close escorts (2 heavy cruisers, 1 light cruiser and 9 destroyers) sails towards it's target. Nearby, providing air cover, are a light carrier, a seaplane carrier and 3 destroyers.

- At what speed do they travel? I've seen sources that say that it would not be more than 10 knots.
- Are they zig-zagging? I assume they do. What does this to their speed in terms of distance covered?
- What formation do they use? They will have to consider air, sea and underwater threats.

2. Suddenly one of the troopships get's hit by a torpedo(es).

- Does the invasionfleet attempt to rescue the ship or is it abandoned?
- How many destroyers are despatched to hunt for the submarine(s) while the invasionfleet heads on (I assume)?
- How long do the escorts hunt for the submarine(s)? More importantly, how many attack runs do they make and how many depthcharges do they dispense while doing so?
 
Not submarine related but I recommend you research the Battle of the Bismarck Sea and some of the convoys running down the Slot that got beat up pretty bad to see how the Japanese reacted to ships getting sunk and damaged during the convoy's transit.
 
For an effective Dutch anti Japanese strategy have them "do a Poland" and concentrate on breaking Japanese Cyphers pre war.

With this information the Dutch submarines can always be in the right place to intercept high value ships and reach havoc against the substantial number of ships not in Convoy.

this was the OTL reason for the american successful submarine campaign. .

cheers Hipper.

Dutch did take a strong interest in IJN signals. All I have is secondary items from US publication s on the Pacific War. So, its not clear what sucess they had with pennetrating any codes or encryption. One item indicated they had some sucess with signals analysis.

The Dutch, US, and Brits had a system set up by late summer 1941 for sharing signals intel. However the IJN habit of changing encryption or code keys before any major operation, and skill at signals deception prevented any widespread sucess from November 1941 through March 1942.
 
HJ Tulp,

Okay, I guess folks have established that there can be no Dutch-wank. However, since that clearly is not what you're seeking to write, I strongly recommend that you read The Dutch Naval Air Force Against Japan by Tom Womack.

This book provides tremendous levels of detail on the operations of Dutch aircraft, includes a couple of useful maps detailing extent of Japanese air coverage during the campaign, and also supplies details on some of the Dutch submarine, naval and even land operations. It nicely illustrates challenges faced by the Dutch effort, as well as the chaotic conditions. I think it would prove very useful.

If you want to depict the Dutch as going full-on jeune ecole and have an interesting story, I'd suggest a few things.

First, have the Dutch emphasize decentralized operations, from small, unobtrusive sub and seaplane bases, and from tenders, coordinated by radio.
Second, bump up submarine strength somewhat. Provide plausibly more/better boats, training and war-readiness.
Third, have the Dutch stress torpedo carrying aircraft. They need more of them, and the most capable types available. Many will have to be seaplanes/floatplanes. Provision must be made for the latter to operate from unobtrusive bays or tenders.
Fourth, provide more and better fighters. The Demons scored a few successes vs Zeros, but they were really rubbish. Perhaps more of the USAAF P-40s make it into theater; perhaps the Dutch just field more and better fighters of their own.
Fifth, include at least one carefully planned operation that features the Dutch combined arms technique -- a light cruiser or three to scout for a Wolfpack as well as distract Japanese escorts, a group-attack by subs, and maybe a strike by torpedo planes for good measure.

The Dutch will still get clobbered, of course. But such a setting would let you explore the potentials of a jeune ecole approach in this large and complex theater. I think it would be a fascinating timeline.
 
The Japanese would have had total air superiority. Historically the islands were being bombed while the Japanese landing forces were unloading;

The Japanese were able to achieve complete air superiority wherever they both sought to do so, and where their planes had the effective range to operate. But this wasn't everywhere, all the time. The Japanese hadn't the Intel to identify, nor the planes/bases to attack, every possible important target. Nor did Japanese attacks invariably neutralize all Dutch assets in a given area immediately.

The Dutch naval air arm conducted extensive operations in the 'interstices' of the Japanese air campaign. Japanese air power is a crippling factor, but neither an omnipresent nor omnipotent one.

If HJ Tulp is okay with writing a TL where the Dutch will still inevitably lose, he could make quite a fascinating story.
 
HJ Tulp,

Okay, I guess folks have established that there can be no Dutch-wank. However, since that clearly is not what you're seeking to write, I strongly recommend that you read The Dutch Naval Air Force Against Japan by Tom Womack.

This book provides tremendous levels of detail on the operations of Dutch aircraft, includes a couple of useful maps detailing extent of Japanese air coverage during the campaign, and also supplies details on some of the Dutch submarine, naval and even land operations. It nicely illustrates challenges faced by the Dutch effort, as well as the chaotic conditions. I think it would prove very useful.

If you want to depict the Dutch as going full-on jeune ecole and have an interesting story, I'd suggest a few things.

First, have the Dutch emphasize decentralized operations, from small, unobtrusive sub and seaplane bases, and from tenders, coordinated by radio.
Second, bump up submarine strength somewhat. Provide plausibly more/better boats, training and war-readiness.
Third, have the Dutch stress torpedo carrying aircraft. They need more of them, and the most capable types available. Many will have to be seaplanes/floatplanes. Provision must be made for the latter to operate from unobtrusive bays or tenders.
Fourth, provide more and better fighters. The Demons scored a few successes vs Zeros, but they were really rubbish. Perhaps more of the USAAF P-40s make it into theater; perhaps the Dutch just field more and better fighters of their own.
Fifth, include at least one carefully planned operation that features the Dutch combined arms technique -- a light cruiser or three to scout for a Wolfpack as well as distract Japanese escorts, a group-attack by subs, and maybe a strike by torpedo planes for good measure.

The Dutch will still get clobbered, of course. But such a setting would let you explore the potentials of a jeune ecole approach in this large and complex theater. I think it would be a fascinating timeline.

For torpedo carrying aircraft, have the Dutch buy some of these from the Germans:

https://en.wikipedia.org/wiki/Heinkel_He_115

https://en.wikipedia.org/wiki/Fieseler_Fi_167

Both are well suited to the TL you are talking about and the Dutch did by planes from the Germans.

Also, have them equip and train their PBY squadrons to use torpedoes. Make them the originators of that tactic.

For improved fighter defenses. A popular issue on this forum is improving the reputation of the maligned Brewster Buffalo (see my Indian Ocean TL and Fearless Leader's Wake Island TL). OTL the Dutch did do well with their Buffaloes by flying them with half loads of full and ammunition (fine for point defense). Have them take deliveries of their Buffaloes earlier and figure out substantive ways to lighten the aircraft (take out the nose guns for example).

You could even have the Dutch take on a couple of squadrons of Fairey Battles from the British as they phase those out. Not a world beater of an aircraft but it had decent range with 1000 pound warload and if the pilots are trained in overwater navigation and ant-shipping and ASW tactics, they could be a good fit in this theater of operations.

Just spit balling some ideas for you...
 
For torpedo carrying aircraft, have the Dutch buy some of these from the Germans:

https://en.wikipedia.org/wiki/Heinkel_He_115

https://en.wikipedia.org/wiki/Fieseler_Fi_167

Both are well suited to the TL you are talking about and the Dutch did by planes from the Germans.

Also, have them equip and train their PBY squadrons to use torpedoes. Make them the originators of that tactic.

For improved fighter defenses. A popular issue on this forum is improving the reputation of the maligned Brewster Buffalo (see my Indian Ocean TL and Fearless Leader's Wake Island TL). OTL the Dutch did do well with their Buffaloes by flying them with half loads of full and ammunition (fine for point defense). Have them take deliveries of their Buffaloes earlier and figure out substantive ways to lighten the aircraft (take out the nose guns for example).

You could even have the Dutch take on a couple of squadrons of Fairey Battles from the British as they phase those out. Not a world beater of an aircraft but it had decent range with 1000 pound warload and if the pilots are trained in overwater navigation and ant-shipping and ASW tactics, they could be a good fit in this theater of operations.

Just spit balling some ideas for you...

Great ideas, Zheng He!

On the Heinkel: maybe just accelerate development of the Fokker T.VIII by two or three years. Not as fast as the Heinkel, but longer range and an indigenous design.

More Brewsters would be a good fit. Hawks and Demons in greater numbers. Maybe an early purchase of P-40s, too late for European theater but the delivery transferred to the Dutch East Indies.

The PBY torpedo-dropping is entirely plausible, I think.
 
Great ideas, Zheng He!

On the Heinkel: maybe just accelerate development of the Fokker T.VIII by two or three years. Not as fast as the Heinkel, but longer range and an indigenous design.

More Brewsters would be a good fit. Hawks and Demons in greater numbers. Maybe an early purchase of P-40s, too late for European theater but the delivery transferred to the Dutch East Indies.

The PBY torpedo-dropping is entirely plausible, I think.

Accelerate development of the Fokker is a good idea but you probably need both that and the Heinkel. Dutch aircraft industry is going to be pretty limited so they will want to have an import to go along with foreign production. While you are at it, have the Vought Vindicators that were supposed to go to French go to the Dutch in the DEI after the British decide they are not suitable for escort carriers.
 
Accelerate development of the Fokker is a good idea but you probably need both that and the Heinkel. Dutch aircraft industry is going to be pretty limited so they will want to have an import to go along with foreign production. While you are at it, have the Vought Vindicators that were supposed to go to French go to the Dutch in the DEI after the British decide they are not suitable for escort carriers.

Buying some Heinkels and Vindicators would accord with the Dutch practice of buying whatever off-the-shelf designs available to stock the East Indies' forces.

I note that the British considered offering 100 P-40E's in exchange for 18 of KNIL's 36 PBYs, though for unknown reasons the offer was never formally extended. There were also 80 Douglas DB-7's on order, but only 7 were delivered before the invasion.
 

Ming777

Monthly Donor
Another thing was that the IJN never developed a better method of deploying depth charges that was implemented en masse.

The Allies came up with the Hedgehog and Squid, both of which accelerated the decline of the U-boat threat in the Atlantic.
 
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