Earlier Type XXI - informed by Cold War developments

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TheMarcksPlan
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Re: Earlier Type XXI - informed by Cold War developments

Post by TheMarcksPlan » 29 Jul 2020 20:55

kfbr392 wrote:If an opponent can be reached in an underwater start-up, even if the battery capacity is used ruthlessly, then run, carry out an attack in a start-up and force it if necessary ... 20 percent battery capacity is still enough to do a longer Wabo tracking (4-5 hours) ...
kfbr392 wrote: The XXI should attack surfaced, use eyes, FuMB, FuMO (Hohentwiel), and Balkon-GHG to get a picture of the situation. Stay surfaced as long as possible.
These two quotes that you provided (thanks!) appear at first contradictory. The second envisions attacking on the surface initially while the first encourages using the batteries "ruthlessly" to reach a convoy.

In fact they're probably not contradictory: the ideal is a surface approach but underwater approach is possible if the sub is forced under.

Given the proliferation of Allied airpower later in the war, and given the anticipated response to T21 (e.g. more B-24's over the North Atlantic), T21 probably would have been forced to approach submerged in most circumstances.

That's not a firm obstacle to devastating the convoys, however: U-boats had a detection range of around 10 miles depending on weather etc. So if you have 100 boats at sea it's pretty easy to form a picket line that will guarantee contacts. It'd be harder to concentrate in large wolf packs but even 2-5 T21's would be a massive headache for escorts. Five T-21's could launch 90 torpedoes in half an hour, which means most of the convoy is sunk.

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Re: Earlier Type XXI - informed by Cold War developments

Post by Lars » 30 Jul 2020 19:51

But the XII would also be larger than an upgraded VIIC. The larger the more vulnerable to depth charges.

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Re: Earlier Type XXI - informed by Cold War developments

Post by TheMarcksPlan » 30 Jul 2020 22:30

Lars wrote:
30 Jul 2020 19:51
But the XII would also be larger than an upgraded VIIC. The larger the more vulnerable to depth charges.
Fair point, although I wonder about the magnitude of this effect. Does vulnerability scale linearly with hull volume or with hull surface area? If the latter the size effect would be far less predominant than the speed effect.

Had the T12 entered service in 1941 or so, it also would have been able to outrun most British escorts on the surface - a big asset while the air gap persists and before the buildup of radar-equipped ASW air forces.

To me it seems obvious that the KM should have given itself more frontline options than T7/9. After all, the T12's topline performance/size numbers resemble those of the USN's Gato/Balao class subs, which were publicly known. So it's not as if it would have required exceptional imagination.

Again I see a KM that is designing several classes of big-gun ships, aircraft carriers, cruisers, and destroyers, yet doesn't even bother to bring a large fleet submarine (T12) into detailed design. It's possible that the mere redirection of engineering resources from Raeder's raiders to T12 and other submarine projects would have led to T21's genesis earlier.

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Re: Earlier Type XXI - informed by Cold War developments

Post by kfbr392 » 04 Aug 2020 21:30

TheMarcksPlan wrote:
30 Jul 2020 22:30
Again I see a KM that is designing several classes of big-gun ships, aircraft carriers, cruisers, and destroyers, yet doesn't even bother to bring a large fleet submarine (T12) into detailed design.
That is because of the 1935 AGNA. The tonnage limits therein led to a focus on smaller U-Boot types II, VII, and IX in 1935-38 in order to maximize sub qtys.

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Re: Earlier Type XXI - informed by Cold War developments

Post by TheMarcksPlan » 04 Aug 2020 21:48

kfbr392 wrote:
04 Aug 2020 21:30
TheMarcksPlan wrote:
30 Jul 2020 22:30
Again I see a KM that is designing several classes of big-gun ships, aircraft carriers, cruisers, and destroyers, yet doesn't even bother to bring a large fleet submarine (T12) into detailed design.
That is because of the 1935 AGNA. The tonnage limits therein led to a focus on smaller U-Boot types II, VII, and IX in 1935-38 in order to maximize sub qtys.
I agree that's true before '39 or so. But the KM accepted war with Britain by '39 at the latest and was planning programs without regard for the naval agreement. Despite this, there was no serious effort to field something beyond Types VII/IX until 1942.

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Re: Earlier Type XXI - informed by Cold War developments

Post by kfbr392 » 05 Aug 2020 20:26

yeah, well, Reader assumed the war would start in 1944, so no biggie.

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Re: Earlier Type XXI - informed by Cold War developments

Post by Lars » 10 Aug 2020 10:24

I think that was a rationalization on Raeder's behalf. If he didn't assume that the war started in 1944 he wouldn't get his Z-plan big ships.

If the war plan says war starts in 1940, then build only what can be finished before that. That would be destroyers, e-boats, u-boats, minesweepers, auxiliary cruisers etc.

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Re: Earlier Type XXI - informed by Cold War developments

Post by Carl Schwamberger » 12 Aug 2020 04:26

TheMarcksPlan wrote:
29 Jul 2020 20:55
... Five T-21's could launch 90 torpedoes in half an hour, which means most of the convoy is sunk.
That would be bad. Anyone have some reliable data on the ratio of torpedos launched to ships sunk 1943-45?

All I have is for Japanese surface ships which seemed in 1942 to have roughly a 7% hit rate.

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Re: Earlier Type XXI - informed by Cold War developments

Post by TheMarcksPlan » 12 Aug 2020 04:58

Carl Schwamberger wrote:
12 Aug 2020 04:26
TheMarcksPlan wrote:
29 Jul 2020 20:55
... Five T-21's could launch 90 torpedoes in half an hour, which means most of the convoy is sunk.
That would be bad. Anyone have some reliable data on the ratio of torpedos launched to ships sunk 1943-45?

All I have is for Japanese surface ships which seemed in 1942 to have roughly a 7% hit rate.
Would be very bad indeed...

Note that my projection (most of convoy sunk) is based on use of a pattern-running torpedo, unlike the "dumb" torpedoes fired by all (?) navies in 1942. Upthread my sources predicted (IIRC) >90% success rate for a pattern torpedo running amok within a convoy. I projected "only" that most of the convoy would be sunk by 90 such torpedoes because at some point all those torpedoes are either overkill against an unlucky ship or are running patterns amidst a mostly-sunk convoy and therefore don't hit anything.

For a 5-boat wolfpack, it'd probably be better to launch 30-60 homing torpedoes against the escorts on approach and then 30-60 torpedoes from under the convoy after penetrating the screen.

With 60 homing torpedoes fired at escorts, even 10-15% success rate means 6-9 escorts go down/out. That would leave most convoys practically defenseless: you need several escorts working together to sink even a 12-knot sub and many more to sink an 18kn sub. The remaining 30 pattern-running torpedoes can sink 20-30 ships within 30min of contact with probably zero losses to the small wolfpack ("wolf pod"?). And each T21 still has another 5 torpedoes aboard - not sure how long reload for those would take, however. If the convoy's escorts have been denuded by the initial attack it doesn't really matter how long it takes.

Again, the basic math is daunting. Gives a better understanding of why the USN considered it a "nightmare scenario" for the USSR to produce T21-like submarines as fast as the Germans did.

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Re: Earlier Type XXI - informed by Cold War developments

Post by T. A. Gardner » 12 Aug 2020 16:16

Historically, U-boats almost never sank escorts. Sure, they had some successes more on the order of 1 or 2% but that was it. Part of the problem with all of these is that you have to get relatively close to the target to fire. The G7 torpedo had a run range of, depending on model, 5000 to about 15,000 meters. The wakeless electric torpedoes favored by U-boat captains ran 4000 to 7500 meters.

For pattern runners, you really need a much longer ranged torpedo. Using a G7a (wet heater with wake) torpedo on the slowest speed you have the 15,000 meter range--or about 8 NM. It isn't going to run much of a pattern with such a short range unless you fire it at very short range from potential targets.

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Re: Earlier Type XXI - informed by Cold War developments

Post by Carl Schwamberger » 12 Aug 2020 17:11

TheMarcksPlan wrote:
12 Aug 2020 04:58
. Upthread my sources predicted ...
What sources? Expecting the readers to revisit nine pages for a reference is not a good way to win supporters.

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Re: Earlier Type XXI - informed by Cold War developments

Post by TheMarcksPlan » 12 Aug 2020 22:06

Carl Schwamberger wrote:
12 Aug 2020 17:11
TheMarcksPlan wrote:
12 Aug 2020 04:58
. Upthread my sources predicted ...
What sources? Expecting the readers to revisit nine pages for a reference is not a good way to win supporters.
Ha true. Just FYI I'm not here looking for "supporters" - happy to have nobody agree with me so long as I think I'm right.

But I'm all for courteous, productive interlocutors and e-friends even if we don't agree. So I owe you those sources.

One is The Royal Navy and Anti-Submarine Warfare, 1917-1949 by Llewellyn:
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.
I know there's another source I'm recalling re the >90% figure but pressed for time at the moment. Will get back to you.

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Re: Earlier Type XXI - informed by Cold War developments

Post by Tom from Cornwall » 13 Aug 2020 20:24

TheMarcksPlan wrote:
12 Aug 2020 04:58
With 60 homing torpedoes fired at escorts, even 10-15% success rate means 6-9 escorts go down/out.
How well do you think your "wolf pod" can co-ordinate their attack? Would the "pattern run" cover the whole of the area covered by the convoy and its escorts? I'm certainly not a statistician, but doesn't your calculation rely on a rather unlikely perfect spread of torpedoes fired from a perfectly placed set of submarines against a perfectly positioned set of targets? Do any of your sources give a reliability figure for the "pattern running" torpedo? How many dud warheads or dud fuzes or defective "pattern running" mechanisms or defective electrical circuits, etc, etc.

Regards

Tom

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Re: Earlier Type XXI - informed by Cold War developments

Post by Lars » 17 Aug 2020 13:05

I would add: Is there a risk that the U-boats sink one of their own in such a torpedo rich environment?

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Re: Earlier Type XXI - informed by Cold War developments

Post by Carl Schwamberger » 17 Aug 2020 16:14

I recall discussions of the possibility that happened & the validity of sources for alleged incidents. But, that may be a low probability outlier. What would be more useful to the conversation here would be some hard data on the number of actual hits in proportion to those fired. There must be something from German tests, or others when they experimented with 'pattern running' torpedoes. Some sort of count of those actually fired in combat would be even more useful.

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