"Bastard" Electro U-boats From Early 1943?

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Re: "Bastard" Electro U-boats From Early 1943?

Post by DerGiLLster » 26 Dec 2018 01:26

T. A. Gardner wrote:
25 Dec 2018 23:19

Not entirely true, as the USN proved in the late 40's. The GUPPY boats got batteries that used more carefully designed plates that were thinner, greater in number, and purer in quality of material going into them. That increased cell capacity (in terms of ampacity) while keeping the cell the same size. By using new materials like plastics for the shell, they reduced the weight and increased safety as well. In this way, the same size battery could put out more power or last longer.

The USN also in that program, rearranged the interior of the sub to increase efficency of the crew.

Now, the US had the advantage that their boats were larger, and somewhat more redundant, than German boats. For example, on some GUPPY mods, they removed one diesel (out of 4) reducing both surface speed (considered acceptable) and giving more room for other machinery. They simply ran the remaining diesels more and schnorkeled more to keep the batteries charged.
Getting rid of the deck guns and their magazines gave the conversions new space for more batteries. This could be done on something like a Type IX but not on an electroboat.

So, there are things the Germans could have done, even to older designs, to improve underwater performance. Imagine a Type IX that has the deck gun removed, is streamlined as best as possible, has an increased battery capacity by using the magazine and say removing the stern torpedo tubes along with those torpedoes. Maybe some additional rearrangement of things internally as well. Add some air conditioning to improve crew efficency as well. Add the better GHG sonar like the Type XXI got, and you have a pretty going moderately fast underwater sub. It can snorkel and it can outrun slow escorts and has a much better chance of evading depth charges and 18 knot escorts.

Let's assume the result is a 12 knot submerged boat for 1 hour. That's sufficent to render the Flower class obsolete. They are now entirely too slow for ASW work. That's a near paradign shift in a weapons system. That would require the Allies to make big shifts in escort procedures as well as how they attack submarines.

I'd bet that was doable by early 1943.
How would the Allies respond? Do you know any class of ships that knock out this new hypothetical U-Boat? What ships were brought out late in the war, planned post war, for potential submarine use?

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Re: "Bastard" Electro U-boats From Early 1943?

Post by T. A. Gardner » 26 Dec 2018 02:18

DerGiLLster wrote:
26 Dec 2018 01:26
T. A. Gardner wrote:
25 Dec 2018 23:19

How would the Allies respond? Do you know any class of ships that knock out this new hypothetical U-Boat? What ships were brought out late in the war, planned post war, for potential submarine use?
I would expect the Allies to do several things:

1. Continue production of US destroyer escorts as these could make 28 knots. The US stopped at about 500 units in late 1942 and tapered off production. They had planned for about 1000 units and could have kept cranking out more. These would replace older, slower vessels like the Flower class.

2. See the conversion of older British DD into ASW boats in larger numbers. The RN did this postwar, and could have done it during the war.

3. See the introduction of Hedgehog, Squid, Weapon Alpha, and the like more quickly and widely.

4. See improved versions of FIDO and other homing torpedoes put into service earlier

5. See directional sonobouys like the CRT-4 introduced more quickly.

6. See a reduction in depth charges as a primary weapon. I could also see a better version of the K gun introduced to throw the charges into a wider pattern.

There could also be a larger effort by the USAAF and RAF to bomb and destroy the shipyards where the subs are produced reducing the number being introduced into service. Another might be far more mining off known U-boat ports in an effort to sink them as they leave harbor.

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Re: "Bastard" Electro U-boats From Early 1943?

Post by WATU » 22 Oct 2021 17:26

I am three years late to this thread which I enjoyed reading but a few thoughts.
Kurier, the burst transmission never made it to operational status. The Allied Y service could not triangulate on it but by monitoring the trials equipment had been designed that might do the job with good knowledge of the frequencies being used. The kit was not ready when the war ended. Kurier only worked from U-boat to shore as it needed a large aerial. Signals from BdU to the U-boats would still be available for decryption although the Sonderschlussel cyphers were a big problem. Signal security was flawed and often gave BP cribs. Plus captured documents tec.
Schnorkel. Increasing the speed while schnorkelling was not an objective as far as I am aware. Despite being able to travel at 7kts with experience they usually schnorkelled at less than 4kts to minimise the wake and spray. Precise depth-keeping was harder as speed increased. Diesel noise and cavitation would both increase with speed making passive location easier for hunting ships.
Schnorkelling and generally submerged U-boats have very a very poor radius of vision via the periscope. Without air reconnaissance they would have been ineffective in finding targets. With only a few Atlantic convoys at sea at any one time the ocean is virtually empty. Getting a well-equipped and well-trained maritime air arm past Goering would have been a lot harder than upgrading old U-boats.
Time to get on station mid-Atlantic a problem depending on what happens to endurance with the modifications.
The combination of sonobuoys and FIDO was capable of development. Neither was quite the ticket but great efforts. However I am less impressed with MAD which had such a short range of just a few hundred feet. It did well in the Straits of Gibraltar and there might have been some similar choke points off the UK where it would have been useful. Certainly inefficient at open sea.

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Re: "Bastard" Electro U-boats From Early 1943?

Post by T. A. Gardner » 23 Oct 2021 07:02

Lars wrote:
24 Nov 2004 19:29
This is my very first post on this forum, but I believe that I have the greatest chance of a good answer right here as the amount of collective knowledge here is staggering 8O

We all know about the large XXI and smaller XXIII costal electro u-boats that came along during the last months of the war. The XXI was indeed an awesome machine and the Allies were in for a lot of trouble if it had been ready earlier.

The idea of the XXI and XXIII was born during an otherwise depressing meeting between the U-bootwaffe and professor Walther in November 1942. The meeting was about progress in the development of the Walter U-boats, which had a complicated but promising propulsion system. The message was depressing: As usual the Walter U-boats were postphoned and they were still far too expensive in fuel.

However, during the meeting two German engeneers Schuerer and Broecking had a bright idea: If the streamlined hull of the large Walter U-boat was filled with three times the normal battery capacity, the fast electroboat was a reality. The rest is history, as they say.

Now, what-if the Germans decided to spice up the existing U-boats and fill them up with batteries too to improve their underwater performance? It would be a stop gap solution until the real electroboats came off the line but I believe that it could have been implemented almost at once.

Think of this: The large 1,819 tonnes (submerged) XXI electroboat had the following specifications:

17.2 knots submerged top speed
340 miles range under water at 5 knots
4,400 horsepower submerged
372 battery-cells type 44 MAL 740, in total 33,900 Ah

The large 1,232 tonnes (submerged) IXC/40 conventional U-boat had the following specifications:

7.3 knots submerged top speed
63 miles range under water at 4 knots
1,000 horsepower submerged
124 battery-cells type 44 MAL 740, in total 11,300 Ah

Now, if the Germans had decided to increase the battery-capacity of the IXC/40 in late 1942 by, say 50%, it would solve many of the types problems in 1943 and 1944 (especially if a schnorkel was added). Adding 62 batteries to the existing 124 should have been possible by some minor rearangement of the interior decoration. The IXC/40 had 24 torpedos. Reducing that to 20 would free up a lot of space for more batteries. Other modifications which would find more space for batteries were probably also possible.

With 186 batteries, the IXC/40 specifications might look like this with a 50% increase in capabilities:

11 knots submerged top speed
95 miles range at 6 knots
1,500 horsepower submerged.

Increasing the top speed and range by 50% would more than dubble the area the Allied anti-submarine forces would have to scan. By early 1943, the Allied anti-submarine warfare would be much less effective and the U-boatwaffe much more dangerous.

What do you think?

More on batteries here

http://uboat.net/technical/batteries.htm
I don't think it's possible to add 50% more battery to a Type VII or IX. There simply isn't any room in the design for it. You could get maybe 5% more removing the deck guns and ammunition magazine, but there simply isn't room elsewhere in the design for more.

Image

Shifting to something other than lead-acid might have helped, like the Edison nickel-iron or iron-graphite but here you get a major increase in cost and have to start production from scratch using materials in short supply in Germany.

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Re: "Bastard" Electro U-boats From Early 1943?

Post by Helmut0815 » 23 Oct 2021 08:58

Well, regarding the speed submerged, a streamlined hull plus optimized propellers would have made the difference.

Let's compare the WWII types IX and XXI with the actual type 212:

Type IX C/40
Electric power: 740 kW
Weight submerged: 1,250 to
Max. speed submerged: 7.5 kn

Type XXI
Electric power: 3,700 kW
Weight submerged: 1,820 to
Max. speed submerged: 16.5 kn

Type 212
Electric power: 1,700 kW
Weight submerged: 1,830 to
Max. speed submerged: 20 kn

Although the actual type 212 has less than half the power of the WWII type XXI it has a greater underwater speed due to it's perfect streamlined hull and it's modern efficient propeller, which also reduce the noise and make the boat harder to detect.

So modified types VII and IX with streamlined hulls would have been significantly faster even with standard electric engines and battery capacity. Even the fast type XXI could have been much faster with a streamlined hull due to it's strong electric engines.


regards


Helmut

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Re: "Bastard" Electro U-boats From Early 1943?

Post by TheMarcksPlan » 25 Oct 2021 07:31

Helmut0815 wrote:
23 Oct 2021 08:58

Type 212
Electric power: 1,700 kW
Weight submerged: 1,830 to
Max. speed submerged: 20 kn

Although the actual type 212 has less than half the power of the WWII type XXI it has a greater underwater speed due to it's perfect streamlined hull and it's modern efficient propeller
Seems a bit of stretch to suggest a 1990's design as a feasible alternative to Type XXI.

Does anyone have stats on max submerged propeller RPM for these two designs?
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Re: "Bastard" Electro U-boats From Early 1943?

Post by TheMarcksPlan » 25 Oct 2021 07:35

T.A. Gardner wrote:I don't think it's possible to add 50% more battery to a Type VII or IX.
Why not exactly? I'd agree re T7 and perhaps T9C but Type IX-D added ~20% to IXC's pressure hull volume. Just eyeballing your IXC hull diagram, I'd estimate that <10% of the pressure hull is taken by batteries:
Type-IXC-U-boat-plans2.jpg
If you used all the IX-D's volume increment to increase battery volume, that'd be roughly a tripling of battery capacity before any other steps such as removing the deck gun and magazine.

The problem is that speed is proportional roughly to the cube root of HP, so tripling battery capacity means you can run 44% faster than T9's max submerged speed - so roughly 11 knots - for only as long as the T9 could run its max submerged speed.

So even a tripling of battery capacity, alone, doesn't get quite you a real submarine. Maybe streamlining can bump you up past 12kn for a decent interval on 3x the batteries.

If we want to make this discussion informed by the fundamentals of hydrodynamics and propulsion, we could create rough proportional underwater drag profiles for T9 and T21 based on HP at the same speeds (using the speed^3 - HP relationship, adjusted for RPM and therefore propulsive efficiency). We could then approximate how closely a streamlined could get to a T21, then calculate roughly what the bastard Electro Boat could have done.
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Re: "Bastard" Electro U-boats From Early 1943?

Post by TheMarcksPlan » 25 Oct 2021 08:15

WATU wrote:
22 Oct 2021 17:26
Schnorkel. Increasing the speed while schnorkelling was not an objective as far as I am aware. Despite being able to travel at 7kts with experience they usually schnorkelled at less than 4kts to minimise the wake and spray. Precise depth-keeping was harder as speed increased. Diesel noise and cavitation would both increase with speed making passive location easier for hunting ships.
That's roughly my impression too. Schnorkeling wasn't a means of travelling faster, just safer. But it worked: Uboats in Doenitz's late-war in-shore campaign were about as safe per day at sea as they had been in 1941. See Doenitz's Last Gamble: The Inshore Uboat Campaign, 1944-45 by Karl Peterson. The problem was they were too slow and range-limited underwater to get into attacking position unless a convoy ran them over. They were basically manned mines.

And of course the T7/9's of the Inshore Campaign were far more vulnerable to surface escorts, when they got "lucky" enough to attack, than T21 or the ATL Bastard would have been (T21 would have been practically invulnerable, see linked discussion below).
WATU wrote: Schnorkelling and generally submerged U-boats have very a very poor radius of vision via the periscope. Without air reconnaissance they would have been ineffective in finding targets.
One solution is to wage an inshore campaign (i.e. around the Western Approaches) a la 1944-45. A true sub - either T21 or the bastard - can locate a convoy via hydrophones and has sufficient speed and battery capacity to reach an attacking position while submerged. If you put a couple hundred of these subs in the Western Approaches there's not enough room to hide the convoys.

You may be interested in a more recent thread discussing the T21. As shown there, the RN evaluated its anti-fast-sub capabilities in Cold War context (predicting that SU would field T21ish designs) and found that it had nearly no ability to kill them even several years after WW2 ended.
WATU wrote:The combination of sonobuoys and FIDO was capable of development
FIDO has extremely limited utility against a fast sub because it's limited to 12kn. That's a fairly hard limit because a faster torpedo can't pick the submarine signal out of its own background noise. A solution to that problem is years, perhaps decades, away if the Germans field a fast sub in 1943.
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Re: "Bastard" Electro U-boats From Early 1943?

Post by T. A. Gardner » 26 Oct 2021 06:55

TheMarcksPlan wrote:
25 Oct 2021 07:35
T.A. Gardner wrote:I don't think it's possible to add 50% more battery to a Type VII or IX.
Why not exactly? I'd agree re T7 and perhaps T9C but Type IX-D added ~20% to IXC's pressure hull volume. Just eyeballing your IXC hull diagram, I'd estimate that <10% of the pressure hull is taken by batteries:

Type-IXC-U-boat-plans2.jpg

If you used all the IX-D's volume increment to increase battery volume, that'd be roughly a tripling of battery capacity before any other steps such as removing the deck gun and magazine.

The problem is that speed is proportional roughly to the cube root of HP, so tripling battery capacity means you can run 44% faster than T9's max submerged speed - so roughly 11 knots - for only as long as the T9 could run its max submerged speed.

So even a tripling of battery capacity, alone, doesn't get quite you a real submarine. Maybe streamlining can bump you up past 12kn for a decent interval on 3x the batteries.

If we want to make this discussion informed by the fundamentals of hydrodynamics and propulsion, we could create rough proportional underwater drag profiles for T9 and T21 based on HP at the same speeds (using the speed^3 - HP relationship, adjusted for RPM and therefore propulsive efficiency). We could then approximate how closely a streamlined could get to a T21, then calculate roughly what the bastard Electro Boat could have done.
The IX D isn't any better.

Image

Also, battery capacity alone won't raise top speed. You need to streamline the hull, and you probably need to install more powerful motors. Same motors, more battery = same speed for longer time.

Both the VII and IX are very tight designs. They simply have little room to grow as designed. The quickest way to a faster boat is to insert two new sections fore and aft of the conning tower while streamlining the hull as much as possible. That would give the necessary space to fit the motors and battery. Dump the aft torpedoes to allow for auxiliaries like air conditioning (important to crew morale and performance).

Without a stretch there's simply nowhere to stuff more batteries or put in larger electric motors.

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Re: "Bastard" Electro U-boats From Early 1943?

Post by TheMarcksPlan » 26 Oct 2021 13:18

T.A. Gardner wrote:Without a stretch there's simply nowhere to stuff more batteries or put in larger electric motors.
It should be obvious that's what I meant: stretch the IXC hull to IXD length but don't put in any of the IXD's extra stuff except batteries (primarily) and a larger e-motor (much less significant factor). I specifically said use all the extra space for batteries, which leaves other revisions (e.g. deck gun magazine) to accommodate larger e-motors.

The IXD came in several variants, the IXD-2 from your diagram used a lot of its extra space for an extra pair of diesels that can charge the main batteries while main diesels are used for fast cruising. Kriegsmarine Uboats, 1939-1945 (2) from Osprey Publishing, page 9. Those additional engines are circled below:
Type IX-D diagram.png
Obviously that takes a lot of space and it's not necessary for the bastard, which will charge via Schnorkel off the main diesels. Type IXD-1 used 9,000hp of diesels (taking more extra space) to achieve higher surface speed, obviously that's not what you do in the bastard either.

Aside from extra space for diesels, IXD's appear to have used extra space for better crew accommodations because they went on very long voyages. Obviously not what you do with the bastard either.

Re motors, here's a picture of the Type XXI's e-motors:

Image

If you want to reach 17-18kn, that's around what you'll need. If you want to reach 12kn, you'll need something ~1/3 of that size. If the latter, this is mostly a battery issue. The extra space (IXD vs. IXC hull) goes to batteries, larger motors can probably be accommodated by removing the deck gun/magazine (with volume-neutral reshuffling) and the aft tubes.

I'm trying to help you articulate your own idea, not mine:
T. A. Gardner wrote:
25 Dec 2018 23:19
Let's assume the result is a 12 knot submerged boat for 1 hour.
So try to read my suggestions sensibly in that spirit. When I say Type IXD in this context, it should be rather obvious that I mean a IXD hull but not the IXD's internal stuffings.
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Re: "Bastard" Electro U-boats From Early 1943?

Post by TheMarcksPlan » 26 Oct 2021 17:58

So one obvious drawback of using a larger hull to fit more batteries is the extra resistance due to more wetted area. There's really no way around this.

Image

Type IXD's were 4.5% slower underwater than IX-C's (6.9kn vs. 7.3), implying ~12% higher drag (drag ~ speed^2 ; each had 500 bhp e-motors and, I presume, the same propellers).

If we want to make the bastard IX-D do 12kn, our job is now a little harder. Assuming the same propellers - therefore required HP is proportional to speed^3 - we now need 5.26x as much HP or ~2,600 bhp. That's assuming no streamlining of course.

What would be the feasible effect of streamlining? Let's compare Type IX-D's HP-speed to the Type XXI's. As mentioned, we can't make a great comparison because we don't know max propeller RPM yet.

Why does this matter? Because lower RPM means lower horsepower for a given thrust (=resistance at top speed). Theoretical propeller disc efficiency is inversely related to RPM^(2/3) - see here at page 33 for a discussion. Let's set that aside for now.

The other main parameter is wetted area - the total surface area exposed to the sea. Let's call these about even: Type IX-D is 14% longer than T21 (87.6m vs. 76.7m); IX-D is 7% wider and probably >10% taller (due to the "figure 8" pressure hull being taller than wide). In addition, T21's hull shape is, overall, more full for a greater portion of its length:

Image
Image

I would guess T21 has slightly greater total wetted area, actually.

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

Now let's look at speeds and HP.

T21: 17.2kn on 4,900 shp.
T IX-D: 6.9kn on 500 bhp.

Ignoring the bhp/shp distinction for now, and keeping our equal wetted area and propeller assumptions, Type IX-D would require ~7,750 bhp to equal the T21's speed [ 500 * (17.2/6.9)^3 ]

So at first cut, streamlining would have reduced drag by ~35%.

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

That's probably too high, however, because T21 probably had bigger propellers (benefit of wider hull) and the shp/bhp undercounts T21's engine output by a few %.

If we apply a 35% drag reduction to our T9-D via streamlining, we can do 12kn on ~1,700 bhp e-motors [ 0.65 * 2,600]. That's probably doable with decent underwater endurance at higher speeds, given 3x the battery capacity.

I'd really like to find RPM figures for T9-D and T21. Can anyone help?

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

The other suggested approach is to use a "Type VII-D": a T7-C with plugs fore and aft the tower. The problem with that approach, however, is that the square-cube law works against higher speeds for smaller submarines: internal volume (for batteries and motors) escalates with the cube of linear distance; underwater resistance escalates with its square. This is why the T21 had to be bigger than Doenitz would have liked, and why Type XXIII was slower than T21. So I doubt that a "T7-D" bastard e-boat is viable.

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

TMP bookmark: faster Type IX-D
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Re: "Bastard" Electro U-boats From Early 1943?

Post by T. A. Gardner » 26 Oct 2021 22:08

Well, the IXD model proves it is possible to stretch the Type IX design. So, adding 20% + more battery is possible. With streamlining of the hull and larger electric motors it would easily be possible to get 12 knots for 1 hour out of the design, possibly more.

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Re: "Bastard" Electro U-boats From Early 1943?

Post by TheMarcksPlan » 27 Oct 2021 01:30

T. A. Gardner wrote:
26 Oct 2021 22:08
Well, the IXD model proves it is possible to stretch the Type IX design. So, adding 20% + more battery is possible. With streamlining of the hull and larger electric motors it would easily be possible to get 12 knots for 1 hour out of the design, possibly more.
Well maybe. Depends on the numbers/science, not just a hunch. Have a little fun and dip your toes into the basic physics.
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Re: "Bastard" Electro U-boats From Early 1943?

Post by thaddeus_c » 23 Dec 2021 18:30

Helmut0815 wrote:
23 Oct 2021 08:58
Well, regarding the speed submerged, a streamlined hull plus optimized propellers would have made the difference.

Let's compare the WWII types IX and XXI with the actual type 212:

Type IX C/40
Electric power: 740 kW
Weight submerged: 1,250 to
Max. speed submerged: 7.5 kn

Type XXI
Electric power: 3,700 kW
Weight submerged: 1,820 to
Max. speed submerged: 16.5 kn

Type 212
Electric power: 1,700 kW
Weight submerged: 1,830 to
Max. speed submerged: 20 kn

Although the actual type 212 has less than half the power of the WWII type XXI it has a greater underwater speed due to it's perfect streamlined hull and it's modern efficient propeller, which also reduce the noise and make the boat harder to detect.

So modified types VII and IX with streamlined hulls would have been significantly faster even with standard electric engines and battery capacity. Even the fast type XXI could have been much faster with a streamlined hull due to it's strong electric engines.
TheMarcksPl[/i wrote:an post_id=2370561 time=1635143484 user_id=80684]
Seems a bit of stretch to suggest a 1990's design as a feasible alternative to Type XXI.

Does anyone have stats on max submerged propeller RPM for these two designs?
my understanding it had less to do with the decade in which it was developed and more to do with the conception of the vessel? the Types VII and IX were optimized for surface transit and operations, only with the XXI did underwater operation become the primary focus, with a streamlined hull as a result.

the capture of the French Atlantic coast lulled the KM into operations where they didn't need much technological advance from WWI types? possibly if they had continued developing some smaller types (for minelaying, etc.), the result would be in the direction of Elektroboot?

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Re: "Bastard" Electro U-boats From Early 1943?

Post by TheMarcksPlan » 24 Dec 2021 05:01

thaddeus_c wrote:my understanding it had less to do with the decade in which it was developed and more to do with the conception of the vessel?
You're right to question whether the basic physics constraints on sub speed have changed since 1942. AFAICS, however, Type 212 relies on an air-independent propulsion system (fuel cells) that simply wasn't feasible back then. Walther's hydrogen peroxide system was probably the closest to feasible and even that wasn't really feasible.
thaddeus_c wrote:the capture of the French Atlantic coast lulled the KM into operations where they didn't need much technological advance from WWI types? possibly if they had continued developing some smaller types (for minelaying, etc.), the result would be in the direction of Elektroboot?
Probably capture of the French and Norwegian coasts contributed to KM's complacency. Hard to document this, however.

IMO the fundamental problem was the U-boats were mostly Doenitz's domain. He was a one-man show largely dictating tactical and technical developments. While excellent in many respects, he appears to have had little technical imagination and had a sort of tunnel vision on the training/doctrine/personnel issues in which he excelled. This is reminiscent of German panzer generals who were excellent in these aspects as well but failed to notice that their tanks were becoming obsolete until they ran into the T34's and KV's. Countries like Japan and Britain developed high-speed subs during prewar; Germany didn't. That's a colossal failure for the most sub-dependent great power. I'd blame Raeader and the rest of upper Seekriegsleitung. They were too focused on rivalling British surface seapower to give the Ubootwaffe its due.
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