What if the Type 21 U-Boats became operational in 1940?

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Anthonycumia1776
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What if the Type 21 U-Boats became operational in 1940?

Post by Anthonycumia1776 » 22 Oct 2019 04:00

What if they did?

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by HistoryGeek2019 » 22 Oct 2019 18:15

They could still be detected with sonar, and their exhaust pipes and periscopes with radar, so the British and Americans still would have blown them out of the water. Germany was inherently inferior at naval warfare compared to the Allies and never stood a chance.

But that wouldn't prevent the Dönitz apologists from saying, "If we had just sunk a few more ships ... Britain surely would have given up!"

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by T. A. Gardner » 23 Oct 2019 19:43

Well, to start with, not all the technology that went into a Type XXI was available in 1940.

Your 1940 boat wouldn't have a snorkel. This was a Dutch invention and the only reason Germany and the KM adopted it was due to Allied air cover of convoys and maritime patrol. Without that impetus, they would have rejected it as mostly, if not entirely, unworkable.

https://en.wikipedia.org/wiki/Submarine_snorkel
http://uboataces.com/snorkel.shtml
https://uboat.net/technical/schnorchel.htm

None of the electronics like radar and ESM would have been available for installation at that point. The only radar set available was Seetakt and it was a very large, bulky, set unsuitable for use on a U-boat.

The sonar system (Gruppenhochtgerät) was simpler, less effective, and would have to be installed differently from what evolved into the system installed on a late war Type XXI. The Balkon installation wasn't available in 1940, and wouldn't have been fitted. Without this system, just the earlier ones available in 1940, the boat couldn't fire blind submerged. It would require coming to periscope depth to fire using then extant fire controls.

It's interesting to note that Japan had also invented a high underwater speed submarine prior to the war, but nothing came of the technology even as Japan also produced some high underwater speed submarines late in the war that were a rough equivalent of the Type XXI and XXIII, the I 201 class for example.

Image

Submarine # 71: !938, 21 knots submerged.

And, of course there's the world's first high underwater speed submarine, the British R Class from WW 1 that could do 14 knots. Not bad for 1917...

Image

Image

If knowledge of this German development were out, the Allies would develop technologies to counter it in any case.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by TheMarcksPlan » 25 Oct 2019 02:37

The Type XXI's main advantage - high underwater speed - didn't matter much given prevailing German Uboat tactics. They'd attack at night on the surface generally. Only after the Allies developed radar capable of detecting U-boats at night, and deployed aircraft that could destroy them quickly after detection (before they could hide in the deep), did Germany have an incentive to consider a different method of Uboat war.

In other words, I don't see the XXI's being much more successful per boat - let alone per RM invested - than Type VII's were until mid-war. The Type XXI would have allowed 1945 resumption of Uboat war at something like 1942 success/loss rates rather than being an unbeatable weapon. That's a big deal if Germany still has a continent to defend but irrelevant by late in the war.

IMO the biggest early-war adaptation of Type XXI tech would have been the quick-reloading torpedo tubes. A "Type VIII" that was basically just a bigger Type VII with quick-reloading tubes probably would have done significantly more damage per encounter with a convoy.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by Russ3Z » 14 Nov 2019 15:19

Would the Type-XXI's high underwater speed not still give it an advantage when forced to submerge by convoy escorts? Yes, the early-war boats mainly relied on surface attacks, and their smaller size and somewhat-higher speed when surfaced might give them a maneuverability advantage, but nevertheless early-war U-boats were still being sunk by depth-charging.

A Type XXI might thus have a lower kill rate per attack, due to its inferior surface performance, but its underwater speed would likely give it a lower loss rate in return. The high underwater speed has the additional advantage of making it more likely to evade escort attacks more quickly and still have the speed to catch up to the same convoy again.

The main technological counter to a high-speed submerged vessel is a high-speed escort, as improved radar and sonar are of limited effectiveness if the ships employing them can't catch their prey in the first place (think Flower-class difficulties). The trade-off for the British will be to make a relatively smaller number of high-speed escorts vs the larger number of low-speed escorts historically employed, at least in the early years.

Of course this British disadvantage in escort numbers and longer build times is offset by essentially the same trade-off for the Germans, who will likewise have a smaller number of possibly-better U-boats.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by HistoryGeek2019 » 14 Nov 2019 19:09

The type XXI had a submerged speed of 17 knots. A destroyer escort has a speed of over 20 knots.

How did the Germans think this would be a good idea? The destroyer escorts would locate the Type XXI with sonar, catch up to it, then sink it with depth charges.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by Terry Duncan » 14 Nov 2019 19:29

HistoryGeek2019 wrote:
14 Nov 2019 19:09
The type XXI had a submerged speed of 17 knots. A destroyer escort has a speed of over 20 knots.

How did the Germans think this would be a good idea? The destroyer escorts would locate the Type XXI with sonar, catch up to it, then sink it with depth charges.
You are also likely to be looking at things like Squid and Hedgehog turning up early too if there is a threat that makes forward throwing weapons a necessity. Then you would look at things like the acoustic homing torpedoes etc that in reality are end of war/Cold War period - though people might take more notice of Hedy Lamarr in this instance too.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by Takao » 15 Nov 2019 13:26

HistoryGeek2019 wrote:
14 Nov 2019 19:09
The type XXI had a submerged speed of 17 knots. A destroyer escort has a speed of over 20 knots.

How did the Germans think this would be a good idea? The destroyer escorts would locate the Type XXI with sonar, catch up to it, then sink it with depth charges.
Because sonar performance degrades rapidly with increased speed. IIRC, the upper limit was about 15-16 knots. At which point ship's noise and flow noise basically blanked out the sonar.

Also, destroyer escorts & frigates did not appear in numbers until 1942. They could also not be built in the more numerous smaller shipyards, which were turning out the slower corvettes.

They Type XXI's would have been best put to use as stand off platforms firing pattern running torps into a convoy's path.

While fast, the 21s lacked the maneuverability of the 7s. The 21s had a single large rudder that was not directly in the path of water flow from the props, thanks to the shafts and props being slightly angled off the centerline, as opposed to the 7&9 dual rudders in the prop flow.


Further, this WI is somewhat nonsensical, as losses were not that great early in the war. The last 6 months of 1942 saw the loss of roughly as many U-Boats as had been lost since the beginning of the war. There is no reason for the Germans to develop the Type XXI pre-war to have it ready & operational in numbers by 1940.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by T. A. Gardner » 17 Nov 2019 07:56

If you consider WW 2 submarine tactics versus convoys, and the tactics the escorts used, the only advantage the Type XXI gives you in 1940 is a second chance to position for a periscope or even surfaced torpedo attack from the flanks of a convoy.
A 'normal' properly escorted convoy would have a screen of escorts in front of it with interlocking sonar sweeps going to detect any submerged boat in the path of the convoy. Along each flank would be additional escorts, fewer than in front, that acted to prevent surfaced subs from penetrating their screen and getting torpedo shots in on the merchant ships.

I'd think in 1940, a Type XXI with 1940 grade equipment aboard, would attempt a surfaced flank attack just like a Type VII or IX would at night. The difference would be if the Type XXI were caught, it could submerge and sprint forward into the convoy to come up to periscope depth or even re-surface and launch a torpedo attack where a Type VII of IX caught by the escorts could be driven down and held down until the convoy passes out of attack range forcing the sub to spend considerable time setting up for a new attack.

Slow corvettes could still be useful as sensor platforms while a few high speed destroyers were assigned to run down targets found.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by JAG13 » 17 Nov 2019 21:01

Anthonycumia1776 wrote:
22 Oct 2019 04:00
What if they did?
There are a dozen things the Germans could have done that would have made their subs far more effective, the Type XXI wouldnt add much in 1940, they were optimized against threats that didnt exist in 1940.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by TheMarcksPlan » 12 Dec 2019 00:56

“HistoryGeek2019” wrote: The type XXI had a submerged speed of 17 knots. A destroyer escort has a speed of over 20 knots.

How did the Germans think this would be a good idea? The destroyer escorts would locate the Type XXI with sonar, catch up to it, then sink it with depth charges.
If sub-hunting were like a game of “tag” you’d be right: the faster surface ship always catches and kills the slower sub.

That’s not how it works though. Otherwise every Type VII/IX pinged by an escort would have been dead. In fact a solo escort had about <10% damage rate and ~2% kill rate per solo attack on a sub:

Image

(success was higher for groups of attacking escorts and for repeated contacts but it’s still far from a game of tag)
https://www.ibiblio.org/hyperwar/USN/re ... SW-11.html

ASW wasn’t an exact science in WW2: there was always measurement error, confusion caused by underwater cacophony (explosions, propellers, objects etc.), and unobserved evasive action. As the link explains, a faster sub means a greater area of uncertainty and a lower probability of re-establishing contact for further attacks. And that relationship is more than linear with speed.

Given more than twice the speed and the ability for silent running, a Type XXI should be at least 3x as hard to kill via surface ships as a Type VII.
But sub-safety isn’t the main point; sub lethality is. While Type VII’s were decently safe underwater even late in the war (see chapter 7 of the linked study), they were also mostly harmless: lacking good sonar, they couldn’t fire blind and – more importantly – a submerged Type VII was too slow to get in a shot unless a ship almost literally ran over it. Once the schnorkel came online, Uboat losses weren’t bad per day in action – they just weren’t very dangerous to Allied ships.

All of this changes with the Type XXI: it’s swift enough submerged to run down even a “fast” convoy (~11 knots) and it can use sonar and homing torpedoes to target ships from the deep.

These are game-changers. Even the linked USN study declined to predict that the Type XXI could have been defeated.

If we optimistically posit that 20% of Type XXI’s that reach a convoy are destroyed, that means an average of 5 convoy attacks per Type XXI before it’s destroyed. The Type XXI could launch 18 torpedoes in 20 minutes; if 25% of those hit that’s 4.5 ships and most will sink. So say each Type XXI sinks 20 ships (ignore damaged ships for now) before its luck runs out.

A Liberty Ship costs about as much as a Type XXI (~$2mil). Its cargo would be at least as valuable as the ship. That means a 40-1 economic attrition ratio on my assumptions (and a bad manpower loss ratio as well).

40-1 is obviously unsustainable even for the supposedly infinite (but decidedly finite) resources of the West; even 5-1 (where most Type XXI’s don’t survive convoy attacks) versus a Germany spending 20% on submarines would tilt the economic balance dramatically in Axis favor.

I know in other threads I’ve conceded that the Type XXI alone couldn’t have won the war for Germany. The more I read, however, I think that was a premature concession. A Germany that has resolved its USSR issue and can build literally thousands of Type XXI’s would present a problem to which I don’t think there was a solution in the 1940’s or even decades later. Acoustic homing torpedoes in the ASW role weren’t fast enough to beat the Type XXI: the American ASW torpedo did only 15 knots; make it go faster and its noise will blot out its ability to discern sub heading/speed. If Germany had 500 Type XXI’s at sea continuously, there’d be no “gap” through which a convoy could move undetected and the sheer numbers in resultant wolf-packs would overwhelm any feasible convoy escort force.

It might be the case that large-scale, transoceanic industrial communications are impossible against a large force of true modern submarines (as opposed to 1930’s-tech submersibles like Type VII/IX). At least one modern military analyst and former officer has suggested as much. Without the ability to move large American forces overseas, or to support the British economy for industrial production, only an A-bomb massacre could have saved the Allied cause.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by Terry Duncan » 12 Dec 2019 02:29

TheMarcksPlan wrote:
12 Dec 2019 00:56
“HistoryGeek2019” wrote: The type XXI had a submerged speed of 17 knots. A destroyer escort has a speed of over 20 knots.

How did the Germans think this would be a good idea? The destroyer escorts would locate the Type XXI with sonar, catch up to it, then sink it with depth charges.
If sub-hunting were like a game of “tag” you’d be right: the faster surface ship always catches and kills the slower sub.

That’s not how it works though. Otherwise every Type VII/IX pinged by an escort would have been dead. In fact a solo escort had about <10% damage rate and ~2% kill rate per solo attack on a sub:

Image

(success was higher for groups of attacking escorts and for repeated contacts but it’s still far from a game of tag)
https://www.ibiblio.org/hyperwar/USN/re ... SW-11.html

ASW wasn’t an exact science in WW2: there was always measurement error, confusion caused by underwater cacophony (explosions, propellers, objects etc.), and unobserved evasive action. As the link explains, a faster sub means a greater area of uncertainty and a lower probability of re-establishing contact for further attacks. And that relationship is more than linear with speed.

Given more than twice the speed and the ability for silent running, a Type XXI should be at least 3x as hard to kill via surface ships as a Type VII.
But sub-safety isn’t the main point; sub lethality is. While Type VII’s were decently safe underwater even late in the war (see chapter 7 of the linked study), they were also mostly harmless: lacking good sonar, they couldn’t fire blind and – more importantly – a submerged Type VII was too slow to get in a shot unless a ship almost literally ran over it. Once the schnorkel came online, Uboat losses weren’t bad per day in action – they just weren’t very dangerous to Allied ships.

All of this changes with the Type XXI: it’s swift enough submerged to run down even a “fast” convoy (~11 knots) and it can use sonar and homing torpedoes to target ships from the deep.

These are game-changers. Even the linked USN study declined to predict that the Type XXI could have been defeated.

If we optimistically posit that 20% of Type XXI’s that reach a convoy are destroyed, that means an average of 5 convoy attacks per Type XXI before it’s destroyed. The Type XXI could launch 18 torpedoes in 20 minutes; if 25% of those hit that’s 4.5 ships and most will sink. So say each Type XXI sinks 20 ships (ignore damaged ships for now) before its luck runs out.

A Liberty Ship costs about as much as a Type XXI (~$2mil). Its cargo would be at least as valuable as the ship. That means a 40-1 economic attrition ratio on my assumptions (and a bad manpower loss ratio as well).

40-1 is obviously unsustainable even for the supposedly infinite (but decidedly finite) resources of the West; even 5-1 (where most Type XXI’s don’t survive convoy attacks) versus a Germany spending 20% on submarines would tilt the economic balance dramatically in Axis favor.

I know in other threads I’ve conceded that the Type XXI alone couldn’t have won the war for Germany. The more I read, however, I think that was a premature concession. A Germany that has resolved its USSR issue and can build literally thousands of Type XXI’s would present a problem to which I don’t think there was a solution in the 1940’s or even decades later. Acoustic homing torpedoes in the ASW role weren’t fast enough to beat the Type XXI: the American ASW torpedo did only 15 knots; make it go faster and its noise will blot out its ability to discern sub heading/speed. If Germany had 500 Type XXI’s at sea continuously, there’d be no “gap” through which a convoy could move undetected and the sheer numbers in resultant wolf-packs would overwhelm any feasible convoy escort force.

It might be the case that large-scale, transoceanic industrial communications are impossible against a large force of true modern submarines (as opposed to 1930’s-tech submersibles like Type VII/IX). At least one modern military analyst and former officer has suggested as much. Without the ability to move large American forces overseas, or to support the British economy for industrial production, only an A-bomb massacre could have saved the Allied cause.
The homing torpedoes are entirely different to the Type XXI itself, not an essential part of it, so allowing them as well as the sub type well in advance 'just because' is stretching things, unless as I posted earlier, you also allow Hedgehog and Squid for the British.

The notion Germany could build 500 of these subs by 1940 and not see a massive change in British naval production is to ignore reality, though of course that is also much the same for the Germans being able to build 500 subs at all by that time. IIRC the total was something like 37 when war broke out, wasnt it? Also, to maintain 500 at sea needs around 1500 of them to be available, essentially meaning no airforce or army enhancements to the degree they took place.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by TheMarcksPlan » 12 Dec 2019 02:45

Terry Duncan wrote:The notion Germany could build 500 of these subs by 1940
As I said upthread, I don't see any case for the Type XXI being available in 1940 or even being much of a difference maker. They're more expensive but not necessarily all that much better in the conditions of 1940. Probably should have made that more clear.

Re 1943, however, the main attributes of the Type XXI seem realistic. It also seems realistic for the Germans to have adopted something like Type XXI by 43, as discussions related to its development happened in 1941.
Also, to maintain 500 at sea needs around 1500 of them to be available, essentially meaning no airforce or army enhancements to the degree they took place.
Doenitz's quote about 100-100-100 related to the pre-France period; once Germany had the French Atlantic coast the time in transit was greatly reduced.
Germans being able to build 500 subs at all by that time.
Again, I agree re 1940.
By 1943, however, Germany's Uboat-building capacity was much greater OTL and, in many conceivable ATL's, far greater still.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by TheMarcksPlan » 12 Dec 2019 04:45

Terry Duncan wrote:you also allow Hedgehog and Squid for the British.
These weren't magic bullets against slow Type VII/IX's though; kill rate was still pretty low per encounter - 9.9% for American and 23% for British vessels in the last year of the war. https://www.ibiblio.org/hyperwar/USN/re ... SW-11.html (page 125). They were barely more than twice as effective as plain old depth charges. This really drives home that the late-war Schnorkel equipped Uboats weren't so much blown out of the seas as suppressed by aircraft, rendering them too slow and blind to cause great damage.

So again, I don't see the Allies having an effective answer to large-scale deployment of the Type XXI's until/unless they develop a modern high-speed homing torpedo. That would require a serious advance in the ability of sonar/acoustics to filter out the background noise of a fast torpedo and isolate the target. Not sure when that capability matured but AFAIK it wasn't even on the horizon in 1945.

Furthermore, I'm not sure there'd be an answer to a large-scale submarine campaign even right now. Of course a war involving any nation that can deploy hundreds of large submarines is a war in which one of the powers has nukes so we'll definitely never live to see the question answered.

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Re: What if the Type 21 U-Boats became operational in 1940?

Post by Terry Duncan » 12 Dec 2019 10:06

TheMarcksPlan wrote:
12 Dec 2019 04:45
Terry Duncan wrote:you also allow Hedgehog and Squid for the British.
These weren't magic bullets against slow Type VII/IX's though; kill rate was still pretty low per encounter - 9.9% for American and 23% for British vessels in the last year of the war. https://www.ibiblio.org/hyperwar/USN/re ... SW-11.html (page 125). They were barely more than twice as effective as plain old depth charges. This really drives home that the late-war Schnorkel equipped Uboats weren't so much blown out of the seas as suppressed by aircraft, rendering them too slow and blind to cause great damage.

So again, I don't see the Allies having an effective answer to large-scale deployment of the Type XXI's until/unless they develop a modern high-speed homing torpedo. That would require a serious advance in the ability of sonar/acoustics to filter out the background noise of a fast torpedo and isolate the target. Not sure when that capability matured but AFAIK it wasn't even on the horizon in 1945.

Furthermore, I'm not sure there'd be an answer to a large-scale submarine campaign even right now. Of course a war involving any nation that can deploy hundreds of large submarines is a war in which one of the powers has nukes so we'll definitely never live to see the question answered.
They dont need to be magic bullets, they fire forwards, thus allowing even relatively slower escorts to fire them to ensure the sub keeps its distance from a convoy. Subs are always relatively restricted if they cannot surface and use a deck gun to attack shipping, and it was where this was possible subs managed to make the biggest impact, the Type XXI doesnt even have such a weapon, making it great for attacking high value naval targets but a lot less useful for attacking merchant ships. The Germans didnt even have the ability to make 500 Type XXI's by the wars end, let alone by 1939/40, and many of the parts that were made were not compatable for assembly with other parts, the modular idea leading to differences that would not have been quite so impractical in a surface ship, but were critical in a submarine where the hull needed to withstand water pressure and not break up into its component modules.

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