Japanese ASW

I'm currently working (mostly musing to be honest) on a timeline where the Netherlands stays the course on it's Jeune École naval doctrine instead of switching to a more navalist approach in the mid-1930s. The Dutch plan was mainly centered around submarines which were supposed to take out the Japanese invasion fleet heading for Java.

Now I do now that (after they got themselves some working torpedoes) the Americans had quite a field day against the Japanese merchant marine. Mainly because of a cultural contempt against ASW and inter-service rivalry. Defense of Japanese convoys was subpar at most.

The Dutch submarines would not be used against the convoys bringing in supplies but where supposed to sucker-punch the Japanese invasion fleets. How well were those protected against submarines?
 
How well were those protected against submarines?

The invasion convoys were far better protected than the 'regular' convoys later in the war. I don't have all numbers at hand, but a an example, the invasion convoy to Kota Bahru was protected by 3 destroyer divisions and one light cruiser.

Moreover, if you plan an initial strike at the invasion convoys, you'll have a problem : as long as they are outside of the territorial waters and that Japan has not declared war, there is a political/diplomatic risk in attacking first. And later the convoys will be in shallow waters which are more dangerous or subs.
 
The invasion convoys were far better protected than the 'regular' convoys later in the war. I don't have all numbers at hand, but a an example, the invasion convoy to Kota Bahru was protected by 3 destroyer divisions and one light cruiser.

Does that translate in effectiveness against submarines though? How good were those destroyers? For instance I've heard that IJN destroyers only carried 30 depthcharges.

Moreover, if you plan an initial strike at the invasion convoys, you'll have a problem : as long as they are outside of the territorial waters and that Japan has not declared war, there is a political/diplomatic risk in attacking first. And later the convoys will be in shallow waters which are more dangerous or subs.

From what my preliminary findings tell me the plan was to find the Japanese invasion fleet in the narrow straits around Java. By then it would (and was) war anyway. More dangerous for submarines for sure but the main objective was to defeat the Japanese invasionfleet. Casualties were expected. This also explains the high succes and high losses of the Dutch submarine fleet OTL.
 
The Dutch submarines probably would have done very little. Even though the Japanese were in large part done in owing to the strangulation of their merchant marine, protection of actual invasion convoys was a much different matter.

Overall despite the negative reputation the Japanese received for their ASW capabilities prosecuting the campaign against them was very costly for the USN: 1 in 7 submariners perished during the war, a rate unsurpassed by any other military branch.
 
The Dutch submarines probably would have done very little. Even though the Japanese were in large part done in owing to the strangulation of their merchant marine, protection of actual invasion convoys was a much different matter.

I'm not convinced yet ;)

Any idea how good Japanese ASDIC/SONAR was at the start of the war?

Overall despite the negative reputation the Japanese received for their ASW capabilities prosecuting the campaign against them was very costly for the USN: 1 in 7 submariners perished during the war, a rate unsurpassed by any other military branch.

That seems to be a trademark of submarine branches at war given the fact 2 out of 3 German submariners died :eek:
 
I'm not convinced yet ;) Any idea how good Japanese ASDIC/SONAR was at the start of the war?

Adequate. Most destroyers at the time fielded the Type 93 mod. 1 sonar system (introduced circa 1933). This was more or less on par with other systems dating from that era. In 1942 this was upgraded to the model 3.

In an actual landing operation Japanese troopships were heavily escorted by cruisers and destroyers that would have been on the lookout for precisely this sort of thing (merchant marine convoys were paid less attention to for want of escort vessels and lack of interest until losses really started piling up). Also, as evidenced from their historical operations against the Philippines and plans for war with Russia the IJN identified submarines as a credible threat to warships and marked them as priority targets in the absence of anything bigger fielded by the opposition.

That seems to be a trademark of submarine branches at war given the fact 2 out of 3 German submariners died :eek:

Granted they were facing the combined efforts of the USN and RN.
 
That seems to be a trademark of submarine branches at war given the fact 2 out of 3 German submariners died :eek:
It should probably be noted here that a very substantial fraction of the U-boat survivors never went on a war patrol :eek:
 
Adequate. Most destroyers at the time fielded the Type 93 mod. 1 sonar system (introduced circa 1933). This was more or less on par with other systems dating from that era. In 1942 this was upgraded to the model 3.


In an actual landing operation Japanese troopships were heavily escorted by cruisers and destroyers that would have been on the lookout for precisely this sort of thing (merchant marine convoys were paid less attention to for want of escort vessels and lack of interest until losses really started piling up). Also, as evidenced from their historical operations against the Philippines and plans for war with Russia the IJN identified submarines as a credible threat to warships and marked them as priority targets in the absence of anything bigger fielded by the opposition.

According to this source (https://books.google.nl/books?id=L9...MwQ6AEIXDAN#v=onepage&q=type 93 sonar&f=false) at the start of the war only 20 Japanese destroyers were equipped with the Type 93 sonar.

Then there is the amount of depth charges the Japanese destroyers carried.

Shiratsuyu-class, 18 depth charges, sonar and hydrophones installed after the start of the war. 6 present at Java Sea.
Asashio-class, 16 depth charges, 2 present at Java Sea.
Kagero-class, 16 depth charges, 4 present at Java Sea.
Fubuki-class, 18 depth charges, 2 present at Java Sea.

Now this may sound like a lot but that compare that to for example the Flower-class which carried 70 depth charges. There must be a good reason why the IJN doubled the amount of depth charges carried pretty soon after the war started.

The feeling I'm getting is that the Japanese destroyers were fantastic fighting ships, against surface combattants.

Granted they were facing the combined efforts of the USN and RN.

A very unequal fight after 1942 indeed. Then there is the fact that submarines usually go down with all hands.
 
The Dutch started the war with 15 subs in the DEI and eight were lost:

Three were scuttled by their own crews.

One was torpedoed by Japanese submarine while running on the surface.

Two hit mines.

One was sunk by aircraft while submerged in Surabaya harbor.

One was sunk by depth charges.

Take that for what it is worth but the Dutch were pretty aggressive with their boats yet only one was sunk by traditional ASW methods of the time period:

http://uboat.net/allies/warships/types.html?navy=HNMS&type=Submarine
 
It should probably be noted here that a very substantial fraction of the U-boat survivors never went on a war patrol :eek:

And then add the fact that at a certain point even the U-boat training grounds were not safe anymore :eek:
 
Does that translate in effectiveness against submarines though? How good were those destroyers?

Individually, the japanese escorts were not very good, for the reasons you mentionned (few sonar sets & depth charges).
But they presented a sufficient threat so that the sub skipper could not neglect them.
Thus the fact that there were many destroyers escorting the invasion convoys will prevent sustained attacks by submarines.
Which means that the invasion force will take some losses at sea, but that those are perfectly acceptable losses.

What I mean is that a given submarine has a significant probability to close undetected with a convoy. But once he's made his initial attack (successful or not), he will be subject to counterattacks. Whether those counterattacks sink the sub or not is not relevant for the invasion convoy : in any case, it'll prevent further attack on said convoy by the sub.
 
Individually, the japanese escorts were not very good, for the reasons you mentionned (few sonar sets & depth charges).
But they presented a sufficient threat so that the sub skipper could not neglect them.
Thus the fact that there were many destroyers escorting the invasion convoys will prevent sustained attacks by submarines.
Which means that the invasion force will take some losses at sea, but that those are perfectly acceptable losses.

What I mean is that a given submarine has a significant probability to close undetected with a convoy. But once he's made his initial attack (successful or not), he will be subject to counterattacks. Whether those counterattacks sink the sub or not is not relevant for the invasion convoy : in any case, it'll prevent further attack on said convoy by the sub.

Let me first say that I'm not aiming to write a Dutch-wank or a TL where the Allies are certain to win the Pacific War in 1942. I want to explore what would/could have happened if the RNN fought the war it had been building, training and preparing for during practically the whole Interbellum.

That said, the Japanese invasion of Java suffered no losses during the Battle of Java Sea and only four troopships were sunk at Sunda Strait. What I have seen so far suggests that a underwater attack would have been more succesfull. As Zheng He said OTL there were 15 subs in the East Indies. If those 15 subs would each sink only one troopship that's either the end of the eastern invasion fleet or a quarter of the western invasion fleet.
 
Let me first say that I'm not aiming to write a Dutch-wank or a TL where the Allies are certain to win the Pacific War in 1942. I want to explore what would/could have happened if the RNN fought the war it had been building, training and preparing for during practically the whole Interbellum.

That said, the Japanese invasion of Java suffered no losses during the Battle of Java Sea and only four troopships were sunk at Sunda Strait. What I have seen so far suggests that a underwater attack would have been more succesfull. As Zheng He said OTL there were 15 subs in the East Indies. If those 15 subs would each sink only one troopship that's either the end of the eastern invasion fleet or a quarter of the western invasion fleet.

You may want to change how they use their submarines early in the war. Four of the eight subs the Dutch lost were lost by Christmas Day in 1941. Three were lost off Malaysia and one was lost off Brunei and that includes two of their most modern boats (O-16 and O-20). This sounds cold but for your TL maybe you should have the Dutch hold their boats back for defense of Java and Sumatra?
 
You may want to change how they use their submarines early in the war. Four of the eight subs the Dutch lost were lost by Christmas Day in 1941. Three were lost off Malaysia and one was lost off Brunei and that includes two of their most modern boats (O-16 and O-20). This sounds cold but for your TL maybe you should have the Dutch hold their boats back for defense of Java and Sumatra?

That was indeed what OTL Dutch doctrine before 1939 called for :)
Basically the idea was that the light cruisers would scout for the submarines which would attack the Japanese invasion fleet in the entrance of the Java Sea in divisional attacks of five submarines each.
 
Let me first say that I'm not aiming to write a Dutch-wank or a TL where the Allies are certain to win the Pacific War in 1942.
That's good, and I was definitely not trying to kill a wank.
The bottom line of my point was that, even if the Japanese escort capabilities were inferior to the usual reference (RN & USN against U-boat, which for reference was the absolute best), they were not incapable.
Especially when escorts are used in groups, they are always dangerous to subs.

the Japanese invasion of Java suffered no losses during the Battle of Java Sea and only four troopships were sunk at Sunda Strait.
IIRC, those were sunk by Japanese torpedoes.

If those 15 subs would each sink only one troopship that's either the end of the eastern invasion fleet or a quarter of the western invasion fleet.
You'll need 'wolfpack' tactics, and if you look through the records of OTL German wolfpack attacks against Atlantic, you'll find out that it never (or almost never, I can't be totally sure right now) happened that in a wolfpack of 10+ u-boat, each boat sank a merchantman.
And it's also to be noted that your Dutch boat are all, by definition, on their 1st war patrol - thus not at the top of their potential efficiency.
 
That's good, and I was definitely not trying to kill a wank.
The bottom line of my point was that, even if the Japanese escort capabilities were inferior to the usual reference (RN & USN against U-boat, which for reference was the absolute best), they were not incapable.
Especially when escorts are used in groups, they are always dangerous to subs.

Oh I (and the OTL RNN) fully agree. Losses on the Allied side will probably be horrendous.


You'll need 'wolfpack' tactics, and if you look through the records of OTL German wolfpack attacks against Atlantic, you'll find out that it never (or almost never, I can't be totally sure right now) happened that in a wolfpack of 10+ u-boat, each boat sank a merchantman.

The Dutch submarine fleet was 'wolfpack' capable as early as 1931. The periscopeantenna made communication within the division possible. My main source even claims that Dutch tactics were beyond what even the Germans used.

Going through this (https://en.wikipedia.org/wiki/List_of_wolfpacks_of_World_War_II) list of wolfpacks there were wolfpacks that had sink rates of at least one for each boat. Most didn't obviously but there are a few things that should improve the Dutch chances. Strait Karimata is ofcourse much smaller and more narrow than the Atlantic. The Dutch boats are also going to take much risk as per OTL.

And it's also to be noted that your Dutch boat are all, by definition, on their 1st war patrol - thus not at the top of their potential efficiency.

Hmmm maybe. The RNN had been at war for almost three years by 1942 though.
 
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Moreover, if you plan an initial strike at the invasion convoys, you'll have a problem : as long as they are outside of the territorial waters and that Japan has not declared war, there is a political/diplomatic risk in attacking first. And later the convoys will be in shallow waters which are more dangerous or subs.

As early as 26 Nov the US had issued the 'Consider Hostile' order, the equivalent of the Atlantic "Shoot on Sight" order that had the USN attacking German submarines. The Brit and Dutch governments issued similar orders to their Pacific military about the same time. In any case invasion fleets did not approach the DEI until days after US & British territories were attacked.

Economically there is little risk since Allied cargo shipping in the western Pacific had effectively ceased by October 1941, & no one had been sending cargo ships to Japan since the previous summer.
 
Economically there is little risk since Allied cargo shipping in the western Pacific had effectively ceased by October 1941, & no one had been sending cargo ships to Japan since the previous summer.

That's what a trade embargo does to you! Slightly off-topic I did read a article about a Dutch skipper who sailed on a ship that was leased to a Japanese company. He ended up either sailing to Allied lines or grounding the ship.
 
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.
 

Riain

Banned
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.
 
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