"Bastard" Electro U-boats From Early 1943?

[T. A. Gardner]

in my view the French Atlantic bases affected u-boat development, if they had operated from Norway or the Channel some of the issues would have to be dealt with sooner?

after June 1941 the life or death struggle for Germany was in the East, and an open wound was in the Med?

it is almost as if the KM was waging a whole separate war, albeit they were almost forced to send u-boats into the Med, which should have been a time to develop smaller boats?

The Type VII was about as small an ocean-going boat as you could make versus a coastal only submarine.

[TheMarcksPlan]

The Type VII was about as small an ocean-going boat as you could make versus a coastal only submarine.

What's your physics/science-based rationale?

[T. A. Gardner]

The Type VII was about as small an ocean-going boat as you could make versus a coastal only submarine.

What's your physics/science-based rationale?

It's more about industrial engineering. You need a certain amount of space for crew, equipment, fittings, etc., to make the boat effective. The Germans designed the Type VII quite well to ensure this human / equipment component was met. Sure, you could build something smaller like a Seehund two-man submarine, but those were all but worthless because they lacked this human / equipment component in their construction. It isn't just about the physics / mechanical engineering of it.

http://uboataces.com/uboat-type-vii.shtml

[TheMarcksPlan]

The Type VII was about as small an ocean-going boat as you could make versus a coastal only submarine.

What's your physics/science-based rationale?

It's more about industrial engineering. You need a certain amount of space for crew, equipment, fittings, etc., to make the boat effective. The Germans designed the Type VII quite well to ensure this human / equipment component was met. Sure, you could build something smaller like a Seehund two-man submarine, but those were all but worthless because they lacked this human / equipment component in their construction. It isn't just about the physics / mechanical engineering of it.

http://uboataces.com/uboat-type-vii.shtml

Yeah duh but the T7 could reach the US East Coast while the Seehund could barely cross the Channel. That's an obvious and not very useful point.

The obvious point being made is that there is some room between the T7 and a purely coastal submarine, which may have been better for the Mediterranean. I'm not convinced that would have been a worthwhile use of German resources but I'm also convinced that it's a more serious point than to raise the false choice between T7 and Seehund.

[T. A. Gardner]

Yeah duh but the T7 could reach the US East Coast while the Seehund could barely cross the Channel. That's an obvious and not very useful point.

The obvious point being made is that there is some room between the T7 and a purely coastal submarine, which may have been better for the Mediterranean. I'm not convinced that would have been a worthwhile use of German resources but I'm also convinced that it's a more serious point than to raise the false choice between T7 and Seehund.

Not until late in 1942 with the new Type VIIC/42 they couldn't really effectively patrol off the US. But that design was cancelled. The Type VII was originally designed for a war against Britain, possibly France. It's 8,500 mile cruising range doesn't give it much room for patrolling off the US once it arrived.

It was the minimum submarine on the least tonnage the Germans could build that would be truly effective in such a war. And, it pretty much was. Previous designs (Type I to VI) were more coastal submarines.

My point in bringing up Seehund was simply to show what an absolute minimum submarine might be in design, and how that minimum design would be a failure compared to something that is better engineered from the equipment and human standpoint.

[ThatZenoGuy]

I think the 7 is pretty easy to understand as a weapon designed to counter Britain, with less capability to take on America. With the 9's being true 'go anywhere I want' ocean submarines.

Not that the 7 was especially short ranged, but she was smaller than the big cruiser subs like the 9's, Japanese cruiser subs, American cruiser subs, etc. That small size was paid for in lesser abilities in terms of fuel storage and munitions.

[thaddeus_c]

The obvious point being made is that there is some room between the T7 and a purely coastal submarine, which may have been better for the Mediterranean. I'm not convinced that would have been a worthwhile use of German resources but I'm also convinced that it's a more serious point than to raise the false choice between T7 and Seehund.

for my part I was not "choosing" between the Type VII and a smaller Type XXIII (or some other designation) but simply that they became fixed on one type, and one type of operations.

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?

[TheMarcksPlan]

Deleted

[Terry Duncan]

The obvious point being made is that there is some room between the T7 and a purely coastal submarine, which may have been better for the Mediterranean. I'm not convinced that would have been a worthwhile use of German resources but I'm also convinced that it's a more serious point than to raise the false choice between T7 and Seehund.

for my part I was not "choosing" between the Type VII and a smaller Type XXIII (or some other designation) but simply that they became fixed on one type, and one type of operations.

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?

I absolutely got your point - something between T7 and T23 in size. T.A. Gardner, however, does not get that point. I was merely expressing annoyance at this poster's tendency to opine on subjects requiring technical insight without evincing any such insight nor the effort to gain it.

Maybe you should consider just sticking to the discussion itself and not passing comments about other members insights, lack of, or knowledge?

[TheMarcksPlan]

Maybe you should consider just sticking to the discussion itself and not passing comments about other members insights, lack of, or knowledge?

I should. Comment deleted. Apologies to both Terry's.

[TheMarcksPlan]

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).

[kfbr392]

What really was needed in 1943 (actually, in 1939) instead of the Typ XXI was a fast (submerged speed) ~750t one-screw boat with a ~8000nm range that could be used in the operational area "North Cape to Gibraltar".
The XXI was in fact only built because it had already been calculated and pre-designed by May 1943 as a Walter propulsion boat, and Dönitz accepted it in June 1943 despite reservations because of its unnecessarily large size.


In 1944, the topic was revisited and resulted in the Typ XXIX designs.
Personally, my favorite is the Typ XXIX H.

This design was only proposed in the fall of 1944, and of course never built.
It used only 124 battery cells, whereas the XXI had 372. Overall, it would have be a lot faster and easier to build than the Typ XXI, and more suitable for convoy battles in the Western Approaches and around Great Britain.

http://www.hisutton.com/Uboat_XXIXH.html
https://www.secretprojects.co.uk/thread ... boat.28945

[TheMarcksPlan]

What really was needed in 1943 (actually, in 1939) instead of the Typ XXI was a fast ~750t one-screw boat with a ~8000nm range that could be used in the operational area "North Cape to Gibraltar".
The XXI was in fact only built because it had already been calculated and pre-designed by May 1943 as a Walter propulsion boat, and Dönitz accepted it in June 1943 despite reservations because of its unnecessarily large size.


In 1944, the topic was revisited and resulted in the Typ XXIX designs.
Personally, my favorite is the Typ XXIX H.

This design was only proposed in the fall of 1944, and of course never built.
It used only 124 battery cells, whereas the XXI had 372. Overall, it would have be a lot faster and easier to build than the Typ XXI, and more suitable for convoy battles in the Western Approaches and around Great Britain.

http://www.hisutton.com/Uboat_XXIXH.html
https://www.secretprojects.co.uk/thread ... boat.28945

Thanks, I hadn't heard of T29 - even uboat.net doesn't list it on its projects page.

While it certainly would have been an excellent weapon, note some drawbacks vs. T21:

• Slower submerged: 15.5kn vs. 18kn (using design speeds for both)
• Less submerged range: 120nm@6kn vs. 340@5kn (works out to ~240nm@6kn)
• 12 torpedoes vs. 23
• Slower surfaced: 13kn vs. 15.5kn

The submerged range is a big factor: T21 creates ~4x the required search area given its ~2x submerged range.

Submerged range also figures into how much of sprint into attacking position each sub could do, leaving enough battery juice for evasion/escape after attack. T21 can stay submerged an moving for ~2x as long as T29 at equal speed.

T21 could have launched 18 torpedoes in 25min, and still had 5 more for later. From your diagram, it looks like the T29's torpedo room doubles as accommodation, with reloads stored below rather than ready for reload as in T21 (that may be the drawer's choice though). T21's dedicated torpedo loading room took a lot of space, which probably isn't feasible on a smaller boat.

I lean towards believing that Doenitz' fixation on the smallest-possible ocean-going boats was an artifact of pre- and early-war resource constraints that he never overcame mentally. Germany established a 30/mo build rate (aside from bombing impacts) late in the war, which should have been sufficient boats to mount a picket line across the seaways.

That's not to say definitively that either would have been the better use of resources, just that there's tradeoffs. Thanks again for posting.

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I'd actually suggest building something even larger than T21, though not as the main boat and not in Germany's actual 1943 resource constraints. Along with the bigger boat, build bigger torpedoes capable of attacking convoys from standoff range. The bigger boat will be even faster and longer-ranged underwater, assuming equal HP-weight ratios. Or keep the same speed and more torpedo tubes. This would force Allied escorts to sail farther from the convoys - opening gaps for the main type - and/or force more resources thrown into hunter/killer groups and away from the convoys.

[kfbr392]

While it certainly would have been an excellent weapon, note some drawbacks vs. T21:

• Slower submerged: 15.5kn vs. 18kn (using design speeds for both)
• Less submerged range: 120nm@6kn vs. 340@5kn (works out to ~240nm@6kn)
• 12 torpedoes vs. 23
• Slower surfaced: 13kn vs. 15.5kn

The submerged range is a big factor: T21 creates ~4x the required search area given its ~2x submerged range.

Submerged range also figures into how much of sprint into attacking position each sub could do, leaving enough battery juice for evasion/escape after attack. T21 can stay submerged an moving for ~2x as long as T29 at equal speed.

T21 could have launched 18 torpedoes in 25min, and still had 5 more for later. From your diagram, it looks like the T29's torpedo room doubles as accommodation, with reloads stored below rather than ready for reload as in T21 (that may be the drawer's choice though). T21's dedicated torpedo loading room took a lot of space, which probably isn't feasible on a smaller boat.

All true!
Regarding underwater endurance at various speeds I have made these calculations: see screenshot below.
Regarding reload speed: no speed loading possible with this setup; loading time would be similar like in a Type VII, but I suspect even slower since more accommodation needs to be removed before getting to the reserve torpedoes.

On the positive side, compared to the XXI:
- only 33% of batteries (a bottleneck in 1944)
- only ~50% of engines (a bottleneck in 1944)
- only (probably) 3 hull sections instead of 8
- less sonar and radar echo
- ability to snorkel at flank speed
- more maneuverable
- shorter diving time
- greater diving depth (due to circular pressure hull)
- greater resistance to depth charges (boat will „roll with the punches“ more; this phenomenom was in fact reported by XXIII crews, where it applied to great extend)
- 27 crew instead of 57
- shorter working-up/ shakedown time
- only one type needed (XXIX H) instead of 2 (XXI and XXIII); massive economies of scale

[TheMarcksPlan]

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).

On the positive side, compared to the XXI:
- only 33% of batteries (a bottleneck in 1944)
- only ~50% of engines (a bottleneck in 1944)

Yes there's definitely positives to the design.

- ability to snorkel at flank speed

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

- 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. I can blow a spherical ballon that will crush in a few feet of water, shallower than a square metal box...

I mentioned upthread that I suspected T21 used its floor beams to reinforce the structural discontinuity at the "double bubble" join. From pictures I've since seen this seems obviously true:



This is a very strong structure, only marginally less efficient than a circle (weight of the floor beams but you need those anyway). Like a circle, it uses "hoop stress" on ~95% of its surface - all except the bubble-join where it's reinforced by the floor beams.

- 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.

- greater resistance to depth charges (boat will „roll with the punches“ more; this phenomenom was in fact reported by XXIII crews, where it applied to great extend)

Yes, another good point.

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On the other hand, many things cost just as much for T29 as T21:

• All advanced sensor systems, submerged and surfaced
• Communications suite
• Schnorkel
• Periscope
• Torpedoes

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.