"Bastard" Electro U-boats From Early 1943?

[kfbr392]

Regarding underwater endurance at various speeds I have made these calculations: see screenshot below.

I don't quite understand the calculations. From the endurance vs. speed columns I infer you're roughly tracking endurance as correlated to [1 / speed^2]? Horsepower (therefore battery drain) moves roughly with the cube of speed (that's rough because many smaller factors are present such as battery draw efficiency, Reynolds number and therefore friction coefficient, propeller cavitation).

I merely did a linear extrapolation based on the following:
- the measured performance of U 3507 in its final configuration as stated on de.wikipedia.org/wiki/U-Boot-Klasse_XXI
- the fact/assumption that at submerged speed of 6kn a XXI could go 256nm while a XXIX H would go 120nm.
In short: I multiplied the performance (submerged range@speed) of a XXI by the factor 0.469 to arrive at the performance of the XXIX H.

- ability to snorkel at flank speed

I didn't catch this. In the article you linked? I wonder if this really would have worked...

Please use deepL.com to machine translate the German language wikipedia article on Typ XXI. It is very good and comprehensive, because it is mainly based on the books by Eberhard Rössler, the German expert author on Uboats.
You will see that the XXI telescoping snorkel had some serious design flaws. It had too small diameter and was not rigid enough, leading to vibrations at certain snorkel speeds. Plus the periscopes could not be used at underwater speeds of >8kn due to vibrations.
This would not have been the case in XXIX H, which would have used a folding snorkel which stabilized the periscope (a so called "Sehrohrschnorchel" - periscope snorkel). In fact, it probably could have been used very much like a weaving, alternatingly snorkeling and deep-diving Schnellboot to break through the convoy screen at night!

- greater diving depth (due to circular pressure hull)

Your linked article says depth undetermined. It's not necessarily true that circles have greater crush depth - depends on how strongly-built something is.

Please read the German wiki page on this issue also.
The strength of the figure-8 hull of the XXI could not be calculated reliably beforehand and it turned out later that it could not dive deeper than a VII because of that.

- only one type needed (XXIX H) instead of 2 (XXI and XXIII); massive economies of scale

What about Caribbean ops? The first T21 was on its way there when the war ended... And South Atlantic, Indian Ocean.
You might say ignore the peripheral theaters but enables the Allies to concentrate all their ASW in the North Atlantic.

True.
But that is where traffic is concentrated and where the war is won or lost. And successful patrols there mean more Allied tonnage sunk/day/boat.
The boats need to march undetected to north of Ireland, find a convoy, break through the screen, fire the 6 ready torpedoes, disengage, then return to port; use the 4 reloads to target DEs, targets of opportunity, and damaged stragglers. Short patrols of less than 20 days, like in the fall of 1940, close to England. With substantial numbers of XXIX's.
I would argue type XXIX H would have been more effective and survivable than XXI. It could have re-enabled convoy battles in the Western Approaches close to Ireland, an area where uboats have been driven away from since May 1941. According to Rössler, it also featured noise dampening to enable quieter snorkeling, which would have somewhat compensated for its reduced battery capacity.

One XXIX could also shadow an outgoing convoy for days, report its position, evade HUFFDUFF attackers below the surface, and re-enable large scale wolfpack attacks further out in the Atlantic where fewer escorts could be expected.

Additionally, a few XXIX could be sent out further - to Freetown or the US - using older large conventional uboats as milk cows.
But with long patrols, a lot of time is wasted in transit, since these boats (XXI and XXIX) would have marched always submerged at ca. 5-6kn average.

A final judgment might come down to how much cheaper is the T29 and how many more ships would a T21 kill?

T21's ability to throw out 18 torpedoes in 20 minutes, then evade at higher speed for longer, suggests to me that it might have ~3x the killing power of a T29, which probably will cost at least half as much.

Then again there's other factors (bottlenecks, construction/training time, number of boats at sea and therefore reconnaissance). I'd still probably pick the T21 if given only one choice but I can see the other side of the argument.

I can see that point also and agree with you that both concepts had their merit.

The XXIX was conceptualized 15-24 months later than the XXI and thus incorporated some lessons learned from the XXI detailed design and construction.

Also, in parallel to the XXIX, the one-screw Typ XXXI was drawn up in 1944 as a possible successor to the XXI; it had half the number of engines, 75% of the batteries, but still almost the same performance as the XXI. The XXXI too was never built, of course.
This makes it clear that the German officials did not consider the XXI an ideal solution, not even as a boat for long range operations. And definitely not for operations in the North Atlantic.

[thaddeus_c]

I used the Med for a quick reference to the size/type of boat I was speculating upon, but more broadly I meant something that could have been transportable overland, even if in sections. (well suited to the Black Sea)

certainly when they "inherited" so much coastline to defend, some "different" if not smaller boats would have been warranted?

They didn't really rely on the Uboats for coastal defense, however - not to any great degree. Rather the (IMO correct) strategy was to use Uboats to sink shipping, which would reduce Allied strategic mobility and protect Europe in general.

This strategy worked to a greater degree than most commentators realize. Allied shipping shortages were THE constraint on strategic options during 1942-43. Absent the U-boats, Allies probably could have invaded Europe in 1942 - they certainly could have done ROUNDUP in 1943. For roughly 5% of the armaments budget and a small manpower commitment, Uboats bought Germany roughly two years before facing the full might of the Wallies.
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Re transporting Uboats overland in sections, not sure that's really possible. Unlike an Eboat or Siebel Ferry, a Uboat's structural requirements are such that you'd need, basically, to have a final assembly point on the Med/Black seas.

...which isn't a bad idea if Italy, Romania, Bulgaria, or occupied SU had the capability/willingness to host such facilities and had Germany invented modular submarine construction earlier. There was some German shipbuilding happening in Bulgaria, Italy, and occupied SU (Nikolaev), not sure whether they could have been brought up to snuff for Uboats though, absent a crash investment and workforce-relocation/training program. Doenitz and Raeder did discuss moving U-boat production to the Baltic before Ostheer started retreating. I wonder whether the archives contain any detailed analysis of such plans or if they were just notional.


For a Med-optimized sub, what would you imagine? T7 was ~800t, T2 ~250t. I could see a 500t sub being useful and less expensive than T7 for non-coastal Med ops. You don't need 8,500nm range to operate effectively in the Med.

The per-boat savings seems perhaps unjustified, however, by the need to design a whole new boat, invest in new construction facilities, and loss of scale economies for T7/9 production (assuming resources are shifted Med-ward from T7/9).

my posting may have been unclear, IDK about the modular construction, the requirement or "desire" was to have a "transportable" smaller u-boat with Type XXIII, think by the time it was launched they didn't have anywhere to transport it to!? (so I don't know if it was easier or similar to the Type II to move overland)

Hitler, Doenitz, and the Baltic Sea is an interesting account of why they clung to some areas late war.

historically they used S-boats for harassing shipping and laying mines, just IMO, they should have continued development of smaller boats, rather than find in 1944 or 1945 they need a crash program (manned torpedoes and Seehund) of smaller vessels?

the whole premise of this thread is an earlier Elektroboote or otherwise enhanced oceangoing submarine, that could provide the savings in resources to build a number of smaller boats?

[kfbr392]

IMHO, a German Med optimized uboat for 1943 onwards would have had to have the following characteristics:
- assembly in the Med (straits of Gibraltar had become too dangerous) from prefab sections
- ability to march and attack submerged more or less permanently (too many Allied ASV aircraft, escorts, and also shore based radar systems)
- small size in order to not be spotted from the air while at periscope depth (the water was very clear)
- quick diving time
- endurance >2500nm
- at least 2 torpedo tubes and no less than 4 torpedoes

Basically, the XXIII would have almost perfectly fit the bill, albeit on the low end, if it had been lengthened by about 1300mm and been given two torpedo reloads in the bow room. This actually was a consideration in February 1944, but because it would have resulted in delays in XXIII deliveries the proposal was rejected. The wrong decision, IMO.

The XXIX would have been an exellent fit also, on the high end.

[TheMarcksPlan]

Please use deepL.com to machine translate the German language wikipedia article on Typ XXI. It is very good and comprehensive

Somebody added a ton of great info to this article since I last looked at it a year or so ago.

the XXI telescoping snorkel had some serious design flaws. It had too small diameter and was not rigid enough, leading to vibrations at certain snorkel speeds. Plus the periscopes could not be used at underwater speeds of >8kn due to vibrations.
This would not have been the case in XXIX H, which would have used a folding snorkel which stabilized the periscope (a so called "Sehrohrschnorchel" - periscope snorkel).

I was aware of T21's schnorkel problems but not of the proposed fix on T29. Are we confident it would have worked?

It also raises the question of just putting a better schnorkel on T21. In any circumstance in which Germany can build T29, it can modify T21 as well.

But that [North Atlantic] is where traffic is concentrated and where the war is won or lost. And successful patrols there mean more Allied tonnage sunk/day/boat.

THe most successful patrols IIRC - aside from 39-40 - were in the Caribbean.

The boats need to march undetected to north of Ireland, find a convoy, break through the screen, fire the 6 ready torpedoes, disengage, then return to port; use the 4 reloads to target DEs, targets of opportunity, and damaged stragglers. Short patrols of less than 20 days, like in the fall of 1940, close to England. With substantial numbers of XXIX's.

Sounds like a good strategy to try - probably first priority effort whether it's T29 or T21.

The one concern I'd have is that Schnorkels could be detected by Allied aircraft, albeit at reduced radar range. If you concentrate solely on the Western Approaches then the Allies have enough planes that - if they're focused there - they can blanket the area, find the subs, and attack with air/surface cooperation.

If, however, that main effort is supplemented by serious attacks throughout the Atlantic, the Allies can't possibly cover the entire hemisphere with enough planes. That requires at least some long range boats. Even for attacks around Greenland, it's maybe better to send a T21 with twice the torpedoes given the weeks of deployment time required.

I would argue type XXIX H would have been more effective and survivable than XXI. It could have re-enabled convoy battles in the Western Approaches close to Ireland, an area where uboats have been driven away from since May 1941. According to Rössler, it also featured noise dampening to enable quieter snorkeling, which would have somewhat compensated for its reduced battery capacity.

You may be right on the actual designs but I'm more interested in how size selection drives the decision. As I said, anything "small" like a schnorkel that is put into a T29 seeing service maybe in 1946 could also be put into T21.

One XXIX could also shadow an outgoing convoy for days, report its position, evade HUFFDUFF attackers below the surface, and re-enable large scale wolfpack attacks further out in the Atlantic where fewer escorts could be expected.

Assuming the schorkel is really superb. With any kind of swell/waves in the North Atlantic, it becomes difficult to see long-term and high-speed schnorkelling viable. Even if it worked exactly as designed, wouldn't the schnorkel have to be so big/tall that it would give away the boat?

Also, in parallel to the XXIX, the one-screw Typ XXXI was drawn up in 1944 as a possible successor to the XXI; it had half the number of engines, 75% of the batteries, but still almost the same performance as the XXI.

Is this from Rossler? I should probably get a copy...

This makes it clear that the German officials did not consider the XXI an ideal solution, not even as a boat for long range operations.

It definitely wasn't ideal. Upthread I promised a citation to Germans acknowledging that the Walther-boat-derived hull form wasn't ideal. I haven't been able to track down that cite. Do you recall them saying so?

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To return to the ideal size issue... My notion is that if you're choosing between 200 large subs and 300 smaller subs, you go for 300. I.e. the choice Doenitz advocated.

If, however, you're choosing between, say, 700 large subs and 1,050 smaller subs, I think the answer changes. With a 700-sub fleet, you probably have enough coverage already that the marginal reconnaissance value of each additional sub is lower. You want to maximize killing power more.

So T29 is probably a better answer for IRL Germany than T21, but stopping all submarine production in early '43 is the best possible answer.

For a Germany that has an actual chance of a sustained elektroboot campaign - say a Germany that's defeat Russia - a larger sub seems justified because Germany will have the resources to field perhaps a couple thousand uboats.

Finally, in the latter scenario, I could see the Allies trying to adapt by using faster merchants. A 16kn Type C2 cargo ship cost "only" twice as much, per ton, as a Liberty Ship. The Allies could have switched to that kind of shipping (at massive expense), which reduces their losses by a lot. Against those kinds of ships, each additional submerged knot would really count in taking opportunistic shots.

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On the torpedo reload issue, my intuition is that being able to fire 18 torpedoes in 20-25min makes a small wolfpack ("wolfpod") the equivalent of a much larger wolfpack. That 20-25min timeframe fits nicely within the T21's ability - on a full battery - to sprint, maneuver, attack, and evade. The timeline for normal reloads means that each attack comes with another convoy/escort encounter, which doubles the sub's risk of destruction (or viewing it another way, cuts its usefulness by 2/3 per each time it's risked).

To be clear, this is the decisive issue IMO. The longer range isn't sufficient to justify the larger sub as the primary type and maybe not even as a supplemental type. Were it possible to have a dedicated ready-reload chamber on a smaller sub, then definitely go with the smaller sub.

[TheMarcksPlan]

@kfbr392 somewhat off-topic but do you know whether the KM considered using T7/9's as "scouts" for the elektroboots? They still had hundreds of the hulls lying around. I'm thinking they could have left off some torpedoes and associated crew, packed in more provisions. Then send out the older boats to form a recon picket line, not expecting them to attack convoys (just a few torpedoes to defend themselves). As they'd be mostly loitering instead of cruising, they don't need more fuel for longer endurance - just more crew supplies. With schnorkel, the T7/9's were pretty safe at sea, so long as they didn't try to attack convoys.

I could see this not being considered because the crews were all transitioning to elektroboots or being pulled into land formations. Or because the cost of maintaining the boats wasn't worth it.

[kfbr392]

@kfbr392 somewhat off-topic but do you know whether the KM considered using T7/9's as "scouts" for the elektroboots?

Well possible that someone contemplated this, but in reality it took 22 months from build decision for the first XXI to go on a war patrol and in the meantime, the VII and IX boats were asked - and were willing - to sacrifice themselves to tie down Allied anti submarine resources to save civilian German lives and cities. And then the war was over.

[kfbr392]

I was aware of T21's schnorkel problems but not of the proposed fix on T29. Are we confident it would have worked?

Pretty much. This concept was about to be tested on 2 Typ VII C in May 1945, and snorkel speeds up to 11kn were envisioned (on the modified VII C!). It was also called the Oelfkenschnorchel after its inventor. It should have been mature by the end of 1945.

THe most successful patrols IIRC - aside from 39-40 - were in the Caribbean.

Yeah, the most sinkings per single patrol were done by IX boats doing very long cruises in 1941/42. But the ONLY important metric was tons/boat/day of the whole U-Bootwaffe, and that metric was dropping since 1941 as sinkings in the NA were down so much because uboats could not operate close to England anymore, and other factors.

The one concern I'd have is that Schnorkels could be detected by Allied aircraft, albeit at reduced radar range. If you concentrate solely on the Western Approaches then the Allies have enough planes that - if they're focused there - they can blanket the area, find the subs, and attack with air/surface cooperation.

Germany worked on ways to mask the snorkel with radar absorbing materials. Germany in 1944 was aware that Allies were using 9cm, 3cm and 1.5cm radars. Detection range was also contingent on sea state. Germany put passive radar detectors on snorkel heads and/or on masts so the following scenarii are possible:
- the uboat only snorkels at night and goes on a silent dive as soon as the detector reports a radar emitting plane approaching.
- in good weather, the uboat snorkels during daytime and uses the periscope to visually spot approaching planes before they get close
- for ~18h/day, the boat runs deep on silent engines at 5-6kn
The Allies could not be sure they had really picked up a snorkel radar echo, it could also have been flotsam.
Also consider the actual patrols done by XXIII boats around England in 1945. Not a single boat was attacked from the air during war patrol, not a single boat was lost to any anti-submarine weapon during war patrol.

Assuming the schorkel is really superb. With any kind of swell/waves in the North Atlantic, it becomes difficult to see long-term and high-speed schnorkelling viable. Even if it worked exactly as designed, wouldn't the schnorkel have to be so big/tall that it would give away the boat?

The combustion air for the diesel engines was taken from the engine room, the snorkel fed air into the engine room. This enabled the diesel engines to remain running even if the snorkel got submerged for up to 30 seconds (IIRC). The snorkel head had a shut off valve to prevent water ingress, and water that ingressed was seperated down in the boat.

Also, in parallel to the XXIX, the one-screw Typ XXXI was drawn up in 1944 as a possible successor to the XXI; it had half the number of engines, 75% of the batteries, but still almost the same performance as the XXI.

Is this from Rossler? I should probably get a copy...

Yes, nearly all of the info I give here is from Eberhard Rössler, the German expert author on uboats.

On the torpedo reload issue, my intuition is that being able to fire 18 torpedoes in 20-25min makes a small wolfpack ("wolfpod") the equivalent of a much larger wolfpack. That 20-25min timeframe fits nicely within the T21's ability - on a full battery - to sprint, maneuver, attack, and evade. The timeline for normal reloads means that each attack comes with another convoy/escort encounter, which doubles the sub's risk of destruction (or viewing it another way, cuts its usefulness by 2/3 per each time it's risked).

This is very true and the reason why most 1944 German uboat concepts foresaw at least 8 torpedo tubes. Type XXVI W had 10, Type XXXI had 12. It was realized that probably only a single breakthrough into the convoy would ever be possible, and so the ready torpedoes had to be maximized.

The XXIX H was on the low end in this regard. I believe it was intentionally tuned down to be low on resource consumption and complexity.


And yes, pure Victory ship convoys would really have given XXI a very hard time. This was realized in Germany in early 1944 and one of the reasons the Walter drive Typ XXVI W was ordered into limited production (only Hamburg shipyards). It was half the size of the XXI, which was all that was needed for the North Atlantic, another admission that the XXI was too big.
The XXIX was basically a Elektroboat evolution of the XXVI W.
Some XXIX concepts also had Kreislaufdiesel (closed circuit diesel engines, feeding bottled oxygen into the combustion air) propulsion to save on batteries or Walter fuel and still have high underwater speeds independent of outside air.

[TheMarcksPlan]

Re transporting Uboats overland in sections, not sure that's really possible. Unlike an Eboat or Siebel Ferry, a Uboat's structural requirements are such that you'd need, basically, to have a final assembly point on the Med/Black seas.

...which isn't a bad idea if Italy, Romania, Bulgaria, or occupied SU had the capability/willingness to host such facilities and had Germany invented modular submarine construction earlier.

I'm working my way through Rossler's Uboat "bible," noticed that Germany planned exactly this for T23:

those boats destined for operations in the
Mediterranean and the Black Sea would be built by
their foreign outlets in Toulon (Arsenal); Genoa
(Ansaldo); Monfalcone near Trieste (Cantiere
Riuniti); and Nikolayev. On 20 September 1943,
DW was given a contract for a total of 140 of these
small boats, of which 50 would be built at
Hamburg-Finkenwerder, 30 each at Toulon and
Genoa, and 15 each at Monfalcone and Nikolayev.
As early as December, the yard at Odessa (at that
time under Rumanian authority) was mentioned as
suitable for Black Sea boats

T23 sections were to be rail-transportable for final assembly at the foreign ports.

...which isn't surprising, given that a few Germans are/were smart and the utility of this plan is sort of obvious. The only questionable part is assuming Germany still holds the foreign locales for long but you can't build an assumption that you'll lose the war into your planning... [I mean they should have by then, but the appropriate response is to join the resistance rather than building submarines]

[thaddeus_c]

IMHO, a German Med optimized uboat for 1943 onwards would have had to have the following characteristics:
- assembly in the Med (straits of Gibraltar had become too dangerous) from prefab sections
- ability to march and attack submerged more or less permanently (too many Allied ASV aircraft, escorts, and also shore based radar systems)
- small size in order to not be spotted from the air while at periscope depth (the water was very clear)
- quick diving time
- endurance >2500nm
- at least 2 torpedo tubes and no less than 4 torpedoes

Basically, the XXIII would have almost perfectly fit the bill, albeit on the low end, if it had been lengthened by about 1300mm and been given two torpedo reloads in the bow room. This actually was a consideration in February 1944, but because it would have resulted in delays in XXIII deliveries the proposal was rejected. The wrong decision, IMO.

The XXIX would have been an exellent fit also, on the high end.

thanks for highlighting the Type XXIX, they had a "manic" development program as their situation worsened, and with all the plans (and speculative types) had not really noticed that one.

when we discuss the smaller uboats and mini subs, recall one problem was launching them, think the Seeteufel tracked boat was an innovative design. if they had launched that and the Seehund earlier the designs might have matured.

[kfbr392]

Greetings Thaddeus.
Seeteufel and Seehund were too small and too slow.
The cramped conditions were too much for the human body to endure for more than a few days.

No, Germany at the end of the war was looking at "big midget submarines" with high underwater and snorkel speeds.
Like Typ XXXIV, a 98t closed-cycle boat, using a S-Boot diesel engine and liquid oxygen storage, which would have been quite formidable for its size. And one where a man could stand up in and stretch every once in a while, also have a bed (one bed to be shared between 4 men) to sleep on.

[thaddeus_c]

Greetings Thaddeus.
Seeteufel and Seehund were too small and too slow.
The cramped conditions were too much for the human body to endure for more than a few days.

No, Germany at the end of the war was looking at "big midget submarines" with high underwater and snorkel speeds.
Like Typ XXXIV, a 98t closed-cycle boat, using a S-Boot diesel engine and liquid oxygen storage, which would have been quite formidable for its size. And one where a man could stand up in and stretch every once in a while, also have a bed (one bed to be shared between 4 men) to sleep on.

I was speculating in parallel to the Type XXIII and the other developments you mentioned not as an alternative. (and in any case for "short" specific operations yes. for instance the only type available for use at Anzio was the manned torpedo Neger)

some of the "big midget subs" mentioned would be hard to imagine (under any scenario) being ready by '43 or early '44 don't you think?

they had already identified the need for a larger diesel engine for the Seeteufel as well as improved tracks, cannot imagine the KM could proceed thru the development of an engine using liquid oxygen as fast as they could prepare more conventional types?

OTOH, my rationale for pressing the Type XXIII forward prior to the Type XXI, is that it seems more feasible to actually produce and it would not monopolize all their production, so you could envision the production of some of the more advanced types?

[ThatZenoGuy]

What about early anti-escort weapons? A big problem was a corvette could outrun a submerged Uboat. So instead of being reactive, we go proactive and salvo-fire slow moving guided 'mines' at them?

Even if they are expensive to build, a whole ship surely is more expensive.

[kfbr392]

some of the "big midget subs" mentioned would be hard to imagine (under any scenario) being ready by '43 or early '44 don't you think?

they had already identified the need for a larger diesel engine for the Seeteufel as well as improved tracks, cannot imagine the KM could proceed thru the development of an engine using liquid oxygen as fast as they could prepare more conventional types?

OTOH, my rationale for pressing the Type XXIII forward prior to the Type XXI, is that it seems more feasible to actually produce and it would not monopolize all their production, so you could envision the production of some of the more advanced types?

The 98 ton boat I mentioned was designed in 1945, based on its Roman number.
The whole midget submarine program only started in 1943 after the Germans had captured similar British crafts. The closed circuit propulsion - feeding oxygen into the recycled combustion air - is a manageable engineering challenge. With 20/20 hindsight, the whole midget submarine program could’ve been started years earlier, yes.

Regarding the XXI and XXIII: The first was too large (for the Western Approaches), the second a bit too small (no reloads). An 800 ton boat could have replaced both from the outset (1943).

[kfbr392]

What about early anti-escort weapons? A big problem was a corvette could outrun a submerged Uboat. So instead of being reactive, we go proactive and salvo-fire slow moving guided 'mines' at them?

There was something under development in 1944: the Ursel anti-destroyer underwater upwards-and-astern firing unguided fin-stabilized cavitating missile:
viewtopic.php?f=20&t=60011

[ThatZenoGuy]

What about early anti-escort weapons? A big problem was a corvette could outrun a submerged Uboat. So instead of being reactive, we go proactive and salvo-fire slow moving guided 'mines' at them?

There was something under development in 1944: the Ursel anti-destroyer underwater upwards-and-astern firing unguided fin-stabilized cavitating missile:
viewtopic.php?f=20&t=60011

Now that is pretty cool! Although it seems like aiming the weapon must've been a nightmare and VERY risky.