Earlier Type XXI - informed by Cold War developments

[TheMarcksPlan]

I checked and it's been 10 years since a thread with "Type XXI" in the title was posted in What If.

Further, none of the old What If threads discuss the RN's late-war and Cold War exercises/research re fast submarines, as discussed by Malcolm Llewellyn-Davis (retired RN, MA/PhD of War Studies, King's College London) in works such as "The Royal Navy and Anti-Submarine Warfare, 1917–49." (hereinafter "RNASW49"). https://books.google.com/books/about/Th ... Nw1H3CJ1wC

This book explodes some AHF conventional wisdom that T21 could have been effectively countered in WW2:



Given T21's top submerged speed of 17.2 knots, WW2 escort groups likely had "practically zero" killing rate against it.

Of course technology continued to advance:

The exercises in 1948–49 with Madden’s 6DF had confirmed that anti-submarine
ships had, as anticipated, a limited capability against a fast submarine. Tactical
procedures were needed, therefore, to take advantage of every fleeting detection.
As for the ships’ systems, while the existing Type 144 Asdic and Squid combination
was reasonably efficient against submarines whose speed was less than 12 knots,
against faster submarines it would only achieve a kill in very favourable
circumstances.85 The main limitations of the system were, firstly, the speed at
which ships could operate the asdic effectively was too low, secondly (and directly
related to the slow ship’s speed), the rate of asdic search was too slow and, finally,
the accuracy of the fire-control solution was constrained by the limitations of the
asdic and the existing ahead-throwing weapons. The ship’s asdic operating speed
was critically dependent on the level of underwater self-noise, which in turn, was
dominated by the interference from the ship’s propellers, the design of the asdic
dome, and the ship’s motion in a heavy seaway. Research was underway into
improved propeller designs as well as ways of silencing existing propellers by
surrounding them with an artificial shield of bubbles. A new experimental asdic
dome had already been fitted to HMS Scorpion during 1946, which allowed asdic
operation at speeds of 25–28 knots, that is, seven to 10 knots higher than was
previously possible.86 Improving the asdic search rate was partly dependent on the
ship’s speed and partly on the scanning rate of the asdic itself. This had been
appreciated for some time and work was in hand to develop an all-round scanning
asdic, but this would not become available for many years due to the technical
complexity of the equipment, though a set capable of scanning sector-by-sector
was expected to be available by 1953.87

Nonetheless, asdic usable at higher speeds was only experimental in 1946 and asdic capable of faster search rates envisioned only for 1953.

Note also that ASW technological development had continued after Germany's defeat, owing primarily to the Soviet threat and an expectation that she would capture German submarine technology:

There was not, however, a sudden schism between the wartime German threat and the
new Cold War Russian menace, at least at the political level, and this helps to
explain why the Royal Navy was developing its future anti-submarine doctrine
against a ‘generic’ threat.

RNASW49 at 147.

So can we estimate some range of projections for T21's impact on shipping losses and sub-shipping exchange ratios in the BofA?

Llewellyn summarizes a late-war internal analysis summarizing the then-new submarine threat:

McCrea pointed out that during the period of surface operations by U-boats, roughly
one third of contacts led to an attack, and about a third of these attacks resulted in
a torpedo hit. Most of the failed approaches were due to interceptions by the convoy
escorts. Some of the failures were due to the navigational problem of achieving a
firing position, given the relatively limited engagement envelope of the torpedoes
then in use. For the future, the situation would be different because a fast deep
U-boat would be very difficult to intercept, unless there were revolutionary developments in escorts. Moreover, with pattern-running and homing torpedoes there was
‘… practically no problem of reaching a firing position other than merely getting
within range.’ In addition these torpedoes could be fired without use of the periscope
and each salvo fired was expected to claim a greater number of casualties. In the
future torpedoes were likely, McCrea thought, to have a much longer range, so
that, together with improved underwater performance, future U-boats were not
expected to have much difficulty in converting contacts into attacks

So ~1/9th of Type VII/IX U-Boat contacts resulted in a torpedo hit, whereas the new boats would expect (1) rarely to be stopped from converting contact into attack and (2) to have a higher rate of success with attacks. If only half of T21 contacts scored a hit, that would be a 4.5x increase in kill rate per contact. That T21 could operate submerged at around the same speed as T7/9 on the surface so analyzing their contact/attack dynamics similarly seems broadly appropriate. T21 can't maintain high speed for as long, but it needs far less time engaged to launch more torpedoes.

So that's the contact-dependent side of the attrition equation. What about the Uboat losses side? RNASW49, as cited above, saw "practically zero" success rate for escorts against subs as fast as T21 even in 1949. But let's be super-generous to the RN and say that escorts have nearly half the kill rate per contact. Even so, the T21's shipping-sub exchange rate would be 10x higher than T7/9. So if T7/9's were sinking 50,000 tons per sub lost in '42, T21 would sink 500,000. (assuming all sinkings are by escorts. This wasn't true of course but, after the Schnorkel, aircraft sinkings declined dramatically in share of Uboat kills).

It's not all about the exchange rate except on an infinite time horizon. In terms of tonnage sunk per sub-day, the delta would be closer to that calculated for the per-contact kill rate. Still, over the course of a multi-year BoA, strategic analysis converges on the shipping-sub exchange ratio.

In addition, we'd have to estimate the number of contacts per sub in an "earlier T21" scenario.

We could - and hopefully will - do a more detailed analysis of the scenario. For now, it's sufficient to say that an earlier T21 would have been extremely disruptive to Allied war plans.

-------------------------

One will sometimes hear on AHF that T21 could not have come earlier due to its advanced Sonar. That's not true. The T21's "Balkon GHG" was deployed on older subs in January 1943. https://www.cdvandt.org/GHG1996.pdf

For pre-'43 periods, we have to understand Balkon's utility: it allowed a sub to use its sonar when running near the surface (.e.g. when schnorkelling). While this is a useful feature for making contacts, it's not essential to T21's survivability against escort attack, which is primarily based on its speed.


------------------------

Do I think T21 could have won the war alone? No. At least not unless Germany starts with dozens of them and forces Britain to peace before invading the SU, which seems far-fetched. The Allies could have built gobs of 25-knot merchant ships that would largely evade contact with T21's, for example (though many of these would still be lost). That would have been enormously expensive and, depending when T21 appears, many OTL operations would have been impossible until a massive high-speed merchant fleet became available. So the war's course changes probably but not its outcome unless T21's earlier entry is combined with some narrative that changes other aspects of the war.

A more realistic outcome-changing narrative, IMO, would be something like my "better Barbarossa" ATL's in which Germany plans for strategic defense in the air/sea until after beating all European powers. In that case, earlier/higher focus on U-boat warfare means earlier deployment of T21 in, say, 1943.

[T. A. Gardner]

The problem here is that the tests really only cover one sort of ASW operation: That by a group of surface ships.

It would be interesting to know what type of ships were used in the exercise as that might have an influence on the outcome. Since they were British, that would mean if they were typical late war ASW destroyers they'd likely have 1 or 2 limbo / squid (the Admiralty disfavored the Hedgehog), along with depth charges. They would have one or two ASDIC (aka Sonar) sets aboard but still most likely be using the "searchlight" type that was manually scanned rather than a scanning sonar. This would account for the ascribed "low rate of search."
Searchlight-type sonar typically scanned an 11 degree arc of area, then the operator would move to the next 11 degree sector, etc. That is slow. A scanning sonar sweeps the entire arc of coverage at once and allows for quicker detection. Once a detection is made, the operator can focus on that detection narrowing the sonar's field of 'view.'

Against that, a US group would likely have a CVE or other air asset platform available in this period. That is a game changer. This means that the search for a sub on the prowl starts further from the target (assuming a convoy or the like). That in turn means not running the diesels on snorkel as late war aircraft ASW radar could detect it when in use. By the same token, the Type XXI might have ESM on the snorkel that detects the radar and the sub retracts it to hide from the plane.

USN escorts on the whole in 1944 - 45 are faster than RN ones (24 to 32 knots versus 14 to 30). The USN would be using early scanning sonars by 1945 with the searchlight types being phased out. USN aircraft carry a variety of sonobuoy and can operate up to 6 at once. They have active and passive search with them. The US is using hedgehog, depth charges, and weapon Alpha is coming on line. In addition, they have early homing torpedoes like FIDO which is deployed on both ships and aircraft.

An earlier Type XXI would have put incentive into developing and deploying many of these late war weapons sooner. The Mk 24 FIDO homing torpedo came out in 1943 but could have been deployed say 6 to 12 months earlier in a serious pinch. Trainable hedgehog is not much of a stretch and could have been in service by early 1943 had it been truly necessary.

On the whole, it would have made German subs more survivable and would have increased sinkings, but not by 10 times. It'd be more like 1.25 to 1.5 times in my opinion. The other thing would be that the Allies would respond and the Type XXI would lose most of its advantage within a year or so of operational deployment.

[Tom from Cornwall]

Given T21's top submerged speed of 17.2 knots, WW2 escort groups likely had "practically zero" killing rate against it.

Hi,

There seems no doubt that the Type XXI would have been a greatly increased challenge for Allied convoy escorts, but I don't know who

AHF conventional wisdom

is?

Your statement does raise some questions though:

Has any of your research identified how long the Type XXI can crack on at 17 knots submerged only on it's batteries?

In addition, the data on the number of contacts which led to an attack and a torpedo hit were from "the period of surface operations by U-boats" which would also, I assume have been the period of relatively weaker escort strength for convoys? So not exactly the right baseline to be operating from I guess.

Was a "killing rate" of 30% sufficient to achieve victory in the Battle of Atlantic? Did the "worked-up escort group" include air support? How long were the exercises conducted for?

Regards

Tom

[Takao]

Do we really need another Type XXI thread because the OP wants to move up the Type XXI a whole 3 months? Balkan Gerate was tested in January, 1943, and the first Type XXI was laid down in April, 1943. Nor are any of the new equipment aboard the Type XXI, that would not be there earlier addressed.

He also seems to have based this what if on the Type XXI having nuclear propulsion, and able to maintain 17 knots underwater indefinately, as opposed to the hour or so on a fully charged battery.


Further, none of the issues that prevented the Type XXI from becoming operational earlier are addressed.

Finally, no "just cause" has been given for the Germans to "invent" the Type XXI earlier...Other than the usual hindsight/I'm smarter than the Germans were.

[TheMarcksPlan]

[AHF conventional wisdom] is?

Approximately this:

[T21] would have made German subs more survivable and would have increased sinkings, but not by 10 times. It'd be more like 1.25 to 1.5 times in my opinion.

I.e. a non-analytical list of factors favoring the Allies, completely ignoring any German-favoring factors, followed by a hunch that happens to coincide with one's priors/allegiances.

This hunch is presented against the analysis of Professor W.H. Mcrea of the RN's Directorate of Naval Operational Research which, as cited above, stated the following:

• Whereas T7/9 converted 1/3 of contacts into torpedo attacks, T21 would rarely be prevented from converting contacts into attacks.
• Whereas only 1/3 of T7/9's torpedo attacks resulted in a hit, T21 would rarely miss.

...simple arithmetic gives a 9x delta to sinkings per sub contact.

And that's ignoring T21's ability to fire 3x the torpedoes per attack, something of which Professor Mcrea was unaware at the time of his analysis.

So far we have ~27x killing delta.

Then on the sub losses side, it's even worse. If T21 is 4x harder to kill, the sub-ships exchange ratio would be ~100x times worse. 10x is conservative.

Between an AHF hunch and Professor Mcrea's analysis, I'll go with the latter.

they have early homing torpedoes like FIDO which is deployed on both ships and aircraft.

As I've repeatedly pointed out to you, FIDO is a 12-knot torpedo. Fine against T7/9, not so against T21.

What's more, FIDO had 18.5% success rate - about twice that of depth charges. https://maritime.org/doc/jolie/part1.htm Useful weapon but not a dominator.

USN escorts on the whole in 1944 - 45 are faster than RN ones (24 to 32 knots versus 14 to 30)

What on earth are talking about? Of the American DE's in 1944, only the Buckley's were faster than 21kn and their 24kn speed barely meets your range. https://en.wikipedia.org/wiki/Destroyer ... s_overview

Are you talking about fleet destroyers? They were pretty busy elsewhere in '44.

Regardless, the higher speed is of little value because they can't use asdic above ~20kn.

[Tom from Cornwall]

This hunch is presented against the analysis of Professor W.H. Mcrea of the RN's Directorate of Naval Operational Research which, as cited above, stated the following:
Whereas T7/9 converted 1/3 of contacts into torpedo attacks, T21 would rarely be prevented from converting contacts into attacks.
Whereas only 1/3 of T7/9's torpedo attacks resulted in a hit, T21 would rarely miss.
...simple arithmetic gives a 9x delta to sinkings per sub contact.

And that's ignoring T21's ability to fire 3x the torpedoes per attack, something of which Professor Mcrea was unaware at the time of his analysis.

So far we have ~27x killing delta.

Hmm, I think this is a somewhat more balanced discussion which covers earlier trials with a converted UK S Boat (note that Mccrea was in attendance):

http://rnsubs.co.uk/articles/developmen ... rials.html

And did you deliberately ignore the all-important question (or, like me, do you just not know!)?:

Has any of your research identified how long the Type XXI can crack on at 17 knots submerged only on it's batteries?

Looking at the converted Seraph, it looks like about 15 minutes at top speed. Do we know what that figure was for the Type XXI?

the analysis of Professor W.H. Mcrea of the RN's Directorate of Naval Operational Research

Is the original work available on line? It would be interesting to see what his assumptions were in terms of submarine dynamic performance and sensor performance at high speed; what detection ranges he was using for the escorts ASDIC, radar, etc and whether he included any air assets in the ASW force. Do you know?

Regards

Tom

[T. A. Gardner]

[AHF conventional wisdom] is?

Approximately this:

[T21] would have made German subs more survivable and would have increased sinkings, but not by 10 times. It'd be more like 1.25 to 1.5 times in my opinion.

I.e. a non-analytical list of factors favoring the Allies, completely ignoring any German-favoring factors, followed by a hunch that happens to coincide with one's priors/allegiances.

This hunch is presented against the analysis of Professor W.H. Mcrea of the RN's Directorate of Naval Operational Research which, as cited above, stated the following:

• Whereas T7/9 converted 1/3 of contacts into torpedo attacks, T21 would rarely be prevented from converting contacts into attacks.
• Whereas only 1/3 of T7/9's torpedo attacks resulted in a hit, T21 would rarely miss.

...simple arithmetic gives a 9x delta to sinkings per sub contact.

And that's ignoring T21's ability to fire 3x the torpedoes per attack, something of which Professor Mcrea was unaware at the time of his analysis.

So far we have ~27x killing delta.

Then on the sub losses side, it's even worse. If T21 is 4x harder to kill, the sub-ships exchange ratio would be ~100x times worse. 10x is conservative.

Between an AHF hunch and Professor Mcrea's analysis, I'll go with the latter.

they have early homing torpedoes like FIDO which is deployed on both ships and aircraft.

As I've repeatedly pointed out to you, FIDO is a 12-knot torpedo. Fine against T7/9, not so against T21.

What's more, FIDO had 18.5% success rate - about twice that of depth charges. https://maritime.org/doc/jolie/part1.htm Useful weapon but not a dominator.

USN escorts on the whole in 1944 - 45 are faster than RN ones (24 to 32 knots versus 14 to 30)

What on earth are talking about? Of the American DE's in 1944, only the Buckley's were faster than 21kn and their 24kn speed barely meets your range. https://en.wikipedia.org/wiki/Destroyer ... s_overview

Are you talking about fleet destroyers? They were pretty busy elsewhere in '44.

Regardless, the higher speed is of little value because they can't use asdic above ~20kn.

Unless you look at Kimball and Morse...

https://archive.org/details/methodsofoperati030158mbp

They do a fairly thorough analysis of the U-boat problem from a different perspective. The U-boat problem isn't just one applied to the tactical requirements. The Allies have many more options to counter the Type XXI.

For example, one Kimball and Morse don't discuss is increasing convoy speeds. This could occur by replacing slower merchant ships with faster ones. They discuss things like search rates. If the Allies increased maritime patrols by aircraft, the Type XXI is forced to spend more time submerged to avoid air attack or is driven down more often. This greatly decreases it's search rate.

There are more choices than simply trying to fight the Type XXI head on tactically for the Allies whereas the Type XXI gives the Germans only a tactical advantage in return. It's a better submarine, but it doesn't change the strategic dynamic of the Battle of the Atlantic. So, the problem isn't just a tactical one.

As for escorts: The Buckley, Butler, and Rudderrow classes which comprise about a half of all DE the US built could do 24 knots, but proved capable of 26 to 28 in service.

As for your predictions of kill v. loss rates, these are not going to be linear. The Allies can respond in various ways. They increase the number of escorts for a convoy. They increase the speed of the convoy--something that did occur historically as slower merchant ships were replaced by faster ones newly constructed and as can be demonstrated, slow convoys suffered the most losses during the war.

Kimball and Morse also show that the norm for torpedo firing by a submarine is to fire a spread of 3 or more torpedoes at a target, so that doesn't change from the Type VII / IX to the XXI. Given the torpedoes and fire controls are the same, the odds of a success remain the same it is just the Type XXI has a better chance of getting to a firing position, but that definitely is not a 100% success rate proposition either.

[TheMarcksPlan]

There are more choices than simply trying to fight the Type XXI head on tactically for the Allies

Of course it's not all about convoy battle tactics.

So what's your analytical, non-hunch argument that success beyond the convoy battle would largely neutralize the T21?

They do a fairly thorough analysis of the U-boat problem from a different perspective.

Do they make any specific points that you find convincing? Or are you just citing an entire book?

For example, one Kimball and Morse don't discuss is increasing convoy speeds

Ok but I did discuss that in my OP.

Kimball and Morse also show that the norm for torpedo firing by a submarine is to fire a spread of 3 or more torpedoes at a target, so that doesn't change from the Type VII / IX to the XXI.

...which would allow the T21 to fire two spreads without reloading, versus one for T7/9.

Furthermore, might the "norm" be influenced by tactical considerations that the disparate reloading times might influence? Or should we just assume that the "norm" is some metaphysically-compelled entity?

As for your predictions of kill v. loss rates, these are not going to be linear.

As for my predictions, they plainly aren't linear. Heck they're not even predictions; they're preliminary analysis in which a range of ATL outcomes are suggested, all of them significantly worse than OTL for the Allies.

[T. A. Gardner]

Of course it's not all about convoy battle tactics.

So what's your analytical, non-hunch argument that success beyond the convoy battle would largely neutralize the T21?

1. The Allies bomb the snot out of the U-boat construction yards
2. The Allies bomb the battery factories, and they did indeed do this late in the war. Here those become a bigger priority. There are only three in Germany and a single one builds more than 50% of the batteries.

https://uboat.net/technical/batteries.htm

Between the two, production dries up to a trickle.

Then they bomb the U-boat pens with Tallboy bombs and other precision munitions wrecking many boats and making operations from France difficult.

They step up patrols over the Bay of Biscay so that only a submerged transit, in danger of discovery anyway, is the only possible way to cross. It becomes extremely treacherous for a U-boat of any type to transit, coming or going.

Do they make any specific points that you find convincing? Or are you just citing an entire book?

They provide some examples, but some is theoretical too. For example, they discuss search rates at length. Aircraft have an exponentially greater and faster search rate than submarines. So, the Allies could put up more maritime patrols and have more aircraft searching near convoys. This would drive the U-boat search rate down and in turn reduce the number of targets found.

Or, since U-boat captains preferred the G7E electric torpedo because it is wakeless, the defending escorts can plot a likely position of an attacking sub once an attack is made. That greatly increases their chances of driving down and keeping down the boat preventing a second successful attack. Even if the sub survives this more often, it is unable to make more than one success. Again, it's better than a Type IX but not that much better.

Furthermore, might the "norm" be influenced by tactical considerations that the disparate reloading times might influence? Or should we just assume that the "norm" is some metaphysically-compelled entity?

Reload times are not likely to have a great effect. The boat will have to set up for each target in any case, and if it is discovered, or after the first attack, the convoy can take countermeasures such as a radical course change to mess up a second attack.

As for my predictions, they plainly aren't linear. Heck they're not even predictions; they're preliminary analysis in which a range of ATL outcomes are suggested, all of them significantly worse than OTL for the Allies.

Yes, the Type XXI will be more effective, but it won't be anywhere near 4 to 10 times as effective. It will be more like 1.25 to 2 times and probably more towards the lower end of that range. The biggest reason is the only thing you are changing about it really is it is faster underwater. It uses the same sensors. It uses the same torpedoes. It uses the same fire controls.

Certainly Soviet subs of the 50's versus essentially late WW 2 ASW proved vulnerable to the techniques employed.

The best argument to deal with the Type XXI is limit production and in-service boat availability by bombing the production and harbors where they replenish. The next would be to reduce their effectiveness by forcing them to cruise submerged as much as possible. That greatly reduces their search area and in turn makes it less likely they find targets to attack.

[TheMarcksPlan]

1. The Allies bomb the snot out of the U-boat construction yards
2. The Allies bomb the battery factories, and they did indeed do this late in the war. Here those become a bigger priority. There are only three in Germany and a single one builds more than 50% of the batteries.

That's a fair point, thanks for getting specific.

It's only valid during '44, however. If the T21 enters in '42-'43 the Allied ability to conduct precision strikes at acceptable cost is doubtful. By '44 they can probably neuter new production but if there's already 300 T21's deployed the Allies are going to lose millions of shipping tons. If T21 exchange rate is only 50k tons (about what older U-boats were worth against convoys), that's 15mil shipping tons. Very serious strategic implications. Not war-winning alone, but serious. If T21 exchange rate is 100k tons British production will be seriously impacted.

And focusing bombing effort on T21 would have high opportunity cost.

Then they bomb the U-boat pens with Tallboy bombs and other precision munitions wrecking many boats and making operations from France difficult.

The Allied record against U-Boat facilities was pretty poor. O'Brien has a good discussion of this in How the War was Won. Even it works, it's going to take a huge portion of CBO resources with attendant opportunity cost.

Or, since U-boat captains preferred the G7E electric torpedo because it is wakeless, the defending escorts can plot a likely position of an attacking sub once an attack is made. That greatly increases their chances of driving down and keeping down the boat preventing a second successful attack. Even if the sub survives this more often, it is unable to make more than one success. Again, it's better than a Type IX but not that much better.

One successful attack per encounter would be a massive improvement over Type IX, as discussed above.

Then you move from the single encounter battle to the strategic attrition picture: T21 would survive and return for many more attacks. Their numbers would be building in the Atlantic.

Reload times are not likely to have a great effect.

Not even talking about reloads. T21 has 6 forward tubes so it can do two three-fish spreads successively.

It will be more like 1.25 to 2 times and probably more towards the lower end of that range. The biggest reason is the only thing you are changing about it really is it is faster underwater.

That's a big "only." As the RN's own analysis found, escorts that had a 30% success rate against a 12-knot sub (i.e. 50% faster than T7/9) had "practically zero" chance against T21 speeds. Higher underwater speed (and endurance) is a game-changer.

This is the difference between a submersible and submarine. Fundamentally different.

I still see no real analytical treatment of your "1.25 to 2 times" figure.

[TheMarcksPlan]

And did you deliberately ignore the all-important question (or, like me, do you just not know!)?

T21's underwater endurance figures are given on Wikipedia and elsewhere. https://de.wikipedia.org/wiki/U-Boot-Klasse_XXI

Top speed for ~1.5hrs, 12-14kn for ~10hrs.

The Seraph had lower endurance because it was an older design. The "revolutionary" aspect of T21 was basically to expand the hull to accommodate more batteries.

[T. A. Gardner]

And, tactically, that's the problem with the Type XXI. It has a high underwater speed but low endurance. All the escorts have to do is keep it down and busy, even if they don't kill it, and it is rendered ineffective. The Type XXI isn't "revolutionary" as high underwater speed submarines have been around since 1917 (the British R class). The Japanese produced high speed subs too to little success.

The point is, that higher tactical speed doesn't translate into greater operational or strategic success. The Type XXI wasn't a war winner, but rather a means of survival in a war that needed a paradigm shift that wasn't coming for the Germans with better submarines.

[Takao]

And did you deliberately ignore the all-important question (or, like me, do you just not know!)?

T21's underwater endurance figures are given on Wikipedia and elsewhere. https://de.wikipedia.org/wiki/U-Boot-Klasse_XXI

Top speed for ~1.5hrs, 12-14kn for ~10hrs.

The Seraph had lower endurance because it was an older design. The "revolutionary" aspect of T21 was basically to expand the hull to accommodate more batteries.

The HMS Seraph had lower endurance because it was a smaller design, not because it was older. The British S-Class submarines were roughly the size of the German Type VIIs. She was chosen to be modified, because it could be done quickly, and had already been taken out of service due to damaged sustained.

The hull of the Type XXI was not "expanded to accommodate more batteries." The hull was essentially that of the failed Walther Type XVIII. When the Walther AIP was realized to be a failure, rather than scrap the whole design, it was decided to convert the design into a conventional diesel-electric design. The fuel stores needed for the Walther turbine were quite large, so much of the space could be dedicated to batteries, since the diesels would require far less fuel.

Also, the Seraph was not seen to need the extended range of the Type XXI, not only did the British not know the exact range, but because she was only intended to act as a target for training escorts against the "new" German fast submarines. The Seraph was never intended for combat or to be a British Type XXI equivalent.

[Lars]

If a search area expansion by a factor 10 (to 13) after one hour isn't a serious problem for the Allies I don't know what is:

"Even when located, an alteration of speed and course would help to evade escorts or aircraft-dropped sonar buoys. When escaping at high speed, the Type XXI was almost as fast as most of the Allied escorts and bubbling of water rushing along the hull would make ASDIC location difficult. potential area where a hunted Type XXI, escaping at the silent speed of 5 knots, would be forced to raise the schnorkel again was some 10-13 times greater than an area for conventional U-boat (escaping at 2 knots with a range of 100 miles). With the existing anti-submarine forces search abilities a chance for a kill was therefore greatly reduced."

https://uboat.net/technical/electroboats3.htm

[T. A. Gardner]

If a search area expansion by a factor 10 (to 13) after one hour isn't a serious problem for the Allies I don't know what is:

"Even when located, an alteration of speed and course would help to evade escorts or aircraft-dropped sonar buoys. When escaping at high speed, the Type XXI was almost as fast as most of the Allied escorts and bubbling of water rushing along the hull would make ASDIC location difficult. potential area where a hunted Type XXI, escaping at the silent speed of 5 knots, would be forced to raise the schnorkel again was some 10-13 times greater than an area for conventional U-boat (escaping at 2 knots with a range of 100 miles). With the existing anti-submarine forces search abilities a chance for a kill was therefore greatly reduced."

https://uboat.net/technical/electroboats3.htm

The article cited is one of those All the if's in the world sort that says everything will go just so.

For example, if the Type XXI (or any other boat for that matter) is submerged using extant search technologies its sweep rate, the area it can effective search, becomes that of the sensors. So, when not snorkeling, that would be limited to the periscope and GHG sonar array giving something like an effective 10 nm radius around the boat. The low search rate, in turn translates into a low target detection rate.

The Allies have several things they can do to make this even lower.

First, when a U-boat (regardless of type) is detected by patrolling vessels or aircraft, its position is plotted and then transmitted to all other Allied vessels and airbases / aircraft. For a convoy, they could alter course to avoid the detected boat. If the boat then fails to find the convoy, it is as effective a countermeasure as hounding the sub once found, or sinking it. The sub was made ineffective.

Next, the Allies don't have to necessarily sink the sub to effectively neutralize it. They can simply drive it down and keep it down. Intermittent contact on a particular sub that is not in contact with potential targets would be sufficient for this purpose. That is, say an aircraft--immune to the U-boat--is able to maintain a track or plot of the boat's likely position with sufficient accuracy to allow other Allied assets to move in on it, or avoid it. Further, if the boat has to snorkel and there is an aircraft searching with sufficient accuracy to detect the snorkel, then the U-boat has a problem using it.

For an ASW aircraft, the use of sonobuoys would be initially to establish a track on the target boat. A pattern of sonobuoys, not one but up to six, would be placed by the aircraft and a track established. MAD could be used to confirm the track. The boat might not even know it was being tracked at that point. Again, even ineffective attacks on a Type XXI, where it is tracked on some sensor system would seriously degrade its performance.

All the article looks at is the tactical picture. Tactically, the Type XXI is better than a Type IX for open ocean submarine warfare, but it isn't the claimed ten to thirteen times better. For the Germans, they looked at the problem wrong and came up with the wrong solution. On the other hand, the Allies were able to track with reasonable accuracy the position of U-boats by various means.

What the Germans needed wasn't a better U-boat but better sensors allowing for a greater and faster search rate. That would allow the available boats to engage targets more frequently. It would also allow more data on where Allied ASW assets were which, in turn, means the U-boat can avoid these.

Tactically, all the Allies have to do is stay on a found boat and keep it down. If the U-boat is spending all its time, once detected, evading attack and trying to hide, it isn't attacking shipping so it is a mission fail for the Germans. It doesn't matter one whit that a Type XXI would be harder to kill. It matters that it is not much harder to evade. That is all the Allies need do against one.