WI:Krigesmarine type xxI

[phx1138]

That was actually proposed to modify the existing fleet of U-Boats , but it would have delayed XX-I by year. The speed advantage would have neutralized /offset late war ASW advantage.

I'm not picturing retrofit, which appears to be what this idea meant. I mean, replace the OTL Type IX with a *Type XII which has OTL Type XXI's battery & hull features (& maybe bow & stern sonar arrays?), without the other glitch-prone junk, & start it when a/c begin to make Biscay transits hazardous, around when the flak boats started appearing.

the biggest change I can see is that the Typ XXI class has a speed of 16 knots surfaced and 17 knots submerged. Versus only 7 knots submerged for the Typ VII who fought the battle of the Atlantic OTL. This means that a convoy would not be able to outrun a submerged Typ XXI the way it could a Typ VII. Thus the common strategy of long-range aircraft and minesweepers keeping the u-boat submerged while the convoy makes an evasive maneuver would no longer work. The U-boat has to be hunted and killed, not just 'nailed down'. I have no doubt that with the resources available the convoys would eventually succeed in detecting and killing even a continually submerged u-boat like the XXI, but it would still take them.several months to develop new tactics.

Curiously, this makes it harder for the allies if the XXI were to replace the VII in 1941 then it would be if the XXI were available earlier and superseded the VII before the battle.

Agreed. I also notice nobody's addressed the issue I raised before: what about corvettes & slow convoys? It's all well & good to talk about DDs & a/c with FIDO, but the majority of convoys were escorted with corvettes that (TTL) wouldn't be able to keep up with a dived boat any more, either, & there simply aren't enough DDs to escort all the convoys. Where are they going to come from? And what happens to all the enormous amount of freight that now isn't safe to be sent? That alone is going to bugger things in Europe (& elsewhere!) pretty nicely. That could give real benefits to Japan.

It looks like it means the PQ convoys have to stop entirely. Picture how pissed Stalin will be. How much harder will the Eastern Front turn out to be? (OTOH, how much farther from the Inter-German border will they be at war's end...? Postwar may be better.)

OTOH, it might mean more shipping has to depart Pacific ports, which has knock-ons for simple delay. Iran convoys would seem to be affected, if they go by way of the Pacific. How much does delay of supplies alone affect ops in North Africa?

And if the slow convoys have to stop, what about Bomber Command (just for a start)? How much will ?ops have to be curtailed? How much will food supplies in Britain be affected?

 

[PSL]

I'm not picturing retrofit, which appears to be what this idea meant. I mean, replace the OTL Type IX with a *Type XII which has OTL Type XXI's battery & hull features (& maybe bow & stern sonar arrays?), without the other glitch-prone junk, & start it when a/c begin to make Biscay transits hazardous, around when the flak boats started appearing.

?

KM battery industry could barely keep up with historic demand so doubling battery is out of the Question. But the U-Boat can be hybridized into fast sub , utilizing some of Dr Walters tricks. Schnorkel was developed in 1934 and could be adapted for fast submerged speed early in the war. That fact alone could neutralized most air kills cutting ASW kills 1/2 for the second half of the war.

That means double number of U-Boats at sea in the second half of the war. Schnorkel travel also negates the need for crash diving with massive flooding slits. This in turn allows higher underwater speeds for same sub/motor/tonnage figures. By the same token streamlining the sail allows for further increase in submerged speed for the same U-Boat/motor/battery/tonnage figures. Even with only a few flooding slit the crash dive speed is still respectable...40 seconds to periscope depth, which is couple miles/ clear day- the AC still has to cover to get into DC range. In bad weather such subs likely 30 seconds submerged and virtually impossible to hit.

With a smooth sail & few flooding slits ; 10 knots top submerged dash speed is quite reasonable. This also requires cleaning off the U-Boat hull , so no 'winter-garden' etc. All this can be done mid war instead of the winter garden malarkey and make the sub more stable submerged. Any sub able to dash at 10 knots submerged is twice as difficult to hit with ballistic ASW ; compared to 4-5 knots standard target, but then you will also have only an hour at such dash speeds before need to break off the attack and dive deep and drift.

The real kicker would be to adapt the submerged propeller speed to electric motor -not the diesel. It was estimated that "variable pitch propeller" geared to electric motor- not diesel RPM etc, should immediately increase top-speed of the plain Jane TYPE VII U-Boat from 7 to 12 knots submerged speed. Combined with above mentioned mods it should be able to hit 14-15 knots top speed for an hour or two, while 10 knots submerged could be possible for about 20 hours

 

[McPherson]

the biggest change I can see is that the Typ XXI class has a speed of 16 knots surfaced and 17 knots submerged. Versus only 7 knots submerged for the Typ VII who fought the battle of the Atlantic OTL. This means that a convoy would not be able to outrun a submerged Typ XXI the way it could a Typ VII. Thus the common strategy of long-range aircraft and minesweepers keeping the u-boat submerged while the convoy makes an evasive maneuver would no longer work. The U-boat has to be hunted and killed, not just 'nailed down'. I have no doubt that with the resources available the convoys would eventually succeed in detecting and killing even a continually submerged u-boat like the XXI, but it would still take them.several months to develop new tactics.

Curiously, this makes it harder for the allies if the XXI were to replace the VII in 1941 then it would be if the XXI were available earlier and superseded the VII before the battle.

Snort boats can run fast on the battery but are slowed by their snorts which they use to recharge the batteries by running their diesels submerged to about 4-5 m/s or a fast man running (~ 10-12 knots in that era.) . phx1138 and I disagree about this point a bit as to how much of an edge tactical speed on the battery confers a maneuver edge in battle, but we both know that a noisy snorting boat putting a lot of diesel noise into the water attracts DE's like a light bulb attracts flies. That same snort boat is deaf as a senile shrimp and if it pokes up a radar mast to sniff for LRMPs, it will find them as those birds will home in on the radar transmission.

I think it comes down to density of sensor coverage and how fast the launch platforms get there. The best density and closest proximity that can be arranged in WW II conditions for ASW forces and Mister Type 21 is ye-old-convoy. And since the Type 21 has to come shallow (above the thermocline) to get a sonar bearing to even launch a barrage of relatively short ranged German G-7 pattern running NOISY torpedoes (no more than 3000-5000 meters from the convoy), guess what the chances of being undetected and unengaged and escaping are?

About zero as of April 1943. Again @phx1138 and I disagree about the escape and evasion profile %, but I do not think the tactical speed advantage is there at all. Modern snort boats claim they get in to photograph an American aircraft carrier, but the newsies never tell you about what would happen to aforesaid snort boat if and when once transients are detected. The Germans had a word for that situation. Himmelfarhtskommando. Boom.

 

[AlanJWhite]

Schnorkel was developed in 1934

Not true ...

the "Snorkel" principle was patented in 1916 by a British Engineer James Richardson
"GB 106330 (A) - Improvements in or relating to Submarine or Submersible Boats"
later registered at one of my old stomping grounds, the European Patent Office

The same principle was trialed at sea by the Italians in 1926 , Capt. Pericle Ferretti with H.3
(actually planned for production in the Sirena class but cut for cost)

The Dutch used first a simple pipe in early O class and a more complex design by Jan Jacob Wichers in 1938.

 

[marathag]

If the Allies want to get fancy about it and actually kill U-boats instead of outrun them, then FIDO is going to have to become a 30 knot heavyweight torpedo and their depth charges will need to become larger with about 750 lbs of Composition D with a sink rate of 100 seconds to 300 feet. Complementary to this, the hedgehog mortar will have to become more like the Russian RBU 6000 (easy to do)

Weapon Alpha came from the introduction of the new Nazi subs

if one gets introduced, the other follows soon after. 250 pound warhead, sinks at 40 foot a second, and is time fused to detonate at the calculated depth provided by sonar

The Russians as a consequence STOLE a Fairbanks Morse powered American built diesel locomotive in Iran and reverse engineered it. I believe their version was the TE2?

Close, was the L-L Alco RSD-1 Road Switcher

Soviets called the first copied units the DA-20, and then developed to slightly updated models

that were built in Poland as late as 1989.

They were far more popular in Russian and Polish usage than they were in the USA. Alco pretty much was out of the US market by the mid '50s, taken by EMD and GE 'GP' and 'U' locomotives.
They had roughly 25% of the US diesel market in 1946

 

[AJE]

phx1138 and I disagree about this point a bit as to how much of an edge tactical speed on the battery confers a maneuver edge in battle, but we both know that a noisy snorting boat putting a lot of diesel noise into the water attracts DE's like a light bulb attracts flies.

It attracts DEs only in a relative sense. They have to have a general idea of where the submarine already is in order to get close enough to pick up the submarine on sonar. Otherwise, a well-rafted diesel engine submarine sitting dozens or hundreds of miles from the nearest surface ship won't be picked up very easily by search sonar, which is usually where the submarine likes to be when recharging batteries- they prefer to look for enemy ships only when batteries are charged.

That same snort boat is deaf as a senile shrimp and if it pokes up a radar mast to sniff for LRMPs, it will find them as those birds will home in on the radar transmission.

That's not how radar warning receivers work. The Type XXI in 1943 will be blind because Germany was technologically incapable of building centimetric radar warning receivers in a timely manner like I said, but any competently built submarine force (including late-war German submarines with proper radar warning receivers) can easily avoid LRMPs. The idea that Metox emissions were being homed in on by the Allies was misinformation and in reality they had no such ability to do that, and the late-war RWRs by Germany used crystal oscillators which produced no emissions anyway. A competently equipped diesel submarine has plenty of warning time to dive before a radar-equipped LRMP actually gets within range to spot the submarine. There's always the option of turning off the radar and having the LRMP scan for submarines visually, but we all know how useless that was in the war.

 

[phx1138]

Snort boats can run fast on the battery but are slowed by their snorts which they use to recharge the batteries by running their diesels submerged to about 4-5 m/s or a fast man running (~ 10-12 knots in that era.) . phx1138 and I disagree about this point a bit as to how much of an edge tactical speed on the battery confers a maneuver edge in battle, but we both know that a noisy snorting boat putting a lot of diesel noise into the water attracts DE's like a light bulb attracts flies. That same snort boat is deaf as a senile shrimp and if it pokes up a radar mast to sniff for LRMPs, it will find them as those birds will home in on the radar transmission.

I think it comes down to density of sensor coverage and how fast the launch platforms get there. The best density and closest proximity that can be arranged in WW II conditions for ASW forces and Mister Type 21 is ye-old-convoy. And since the Type 21 has to come shallow (above the thermocline) to get a sonar bearing to even launch a barrage of relatively short ranged German G-7 pattern running NOISY torpedoes (no more than 3000-5000 meters from the convoy), guess what the chances of being undetected and unengaged and escaping are?

About zero as of April 1943. Again @phx1138 and I disagree about the escape and evasion profile %, but I do not think the tactical speed advantage is there at all. Modern snort boats claim they get in to photograph an American aircraft carrier, but the newsies never tell you about what would happen to aforesaid snort boat if and when once transients are detected. The Germans had a word for that situation. Himmelfarhtskommando. Boom.

I think the basis of our disagreement is how we came to our POV. Mine is based heavily on the view from in the boats, & it looks to me like yours isn't. IDK which of us is right, on the facts. So...

On the snorting boat, & the radar mast, I agree--provided there's air on top. I'm far from convinced coverage everywhere was that good all the time, & when it isn't, the *Type XXI is a serious threat. That's even allowing for CVEs or helo-capable tanker-*MACs.

And I come back, again, to the bigger question: where are the fast escorts coming from? Where are the diesels coming from? A million a/c engines proves nothing; the number of makers of marine diesels wasn't enormous, & the OTL production was short for the OTL demand...so what doesn't get built, to make up the difference? Are there other approaches than faster, bigger freighters? Are there other approaches to faster escorts than diesel DEs? (Turbines seem a non-starter; demand there is even greater, & number of producers even smaller.)

Let me posit this: if we equip every tanker & bulk carrier as a *helo-MAC (no TSRs), & fit each *R-5 with a "Hedgehog pod" (what do you say to a *PIAT variant?), could we dispense with corvettes & DEs entirely, & use a single DD as a "beater"? (Yeah, likely need a pair of *R-5s, one with sonobuoys or dipping sonar; I could live with that, if each *MAC operated 6-8.)

On use of the snort, I wonder if it's sensible to run really shallow, to keep the snort head out of the wave action. (Yes, doing this in Biscay is an invitation to suicide. I don't mean then.)

KM battery industry could barely keep up with historic demand so doubling battery is out of the Question. But the U-Boat can be hybridized into fast sub , utilizing some of Dr Walters tricks. Schnorkel was developed in 1934 and could be adapted for fast submerged speed early in the war. That fact alone could neutralized most air kills cutting ASW kills 1/2 for the second half of the war.

That means double number of U-Boats at sea in the second half of the war. Schnorkel travel also negates the need for crash diving with massive flooding slits. This in turn allows higher underwater speeds for same sub/motor/tonnage figures. By the same token streamlining the sail allows for further increase in submerged speed for the same U-Boat/motor/battery/tonnage figures. Even with only a few flooding slit the crash dive speed is still respectable...40 seconds to periscope depth, which is couple miles/ clear day- the AC still has to cover to get into DC range. In bad weather such subs likely 30 seconds submerged and virtually impossible to hit.

With a smooth sail & few flooding slits ; 10 knots top submerged dash speed is quite reasonable. This also requires cleaning off the U-Boat hull , so no 'winter-garden' etc. All this can be done mid war instead of the winter garden malarkey and make the sub more stable submerged. Any sub able to dash at 10 knots submerged is twice as difficult to hit with ballistic ASW ; compared to 4-5 knots standard target, but then you will also have only an hour at such dash speeds before need to break off the attack and dive deep and drift.

The real kicker would be to adapt the submerged propeller speed to electric motor -not the diesel. It was estimated that "variable pitch propeller" geared to electric motor- not diesel RPM etc, should immediately increase top-speed of the plain Jane TYPE VII U-Boat from 7 to 12 knots submerged speed. Combined with above mentioned mods it should be able to hit 14-15 knots top speed for an hour or two, while 10 knots submerged could be possible for about 20 hours

That's very close to what I had in mind, including some of the tactical impacts.

 

[PSL]

Not true ...

the "Snorkel" principle was patented in 1916 by a British Engineer James Richardson
"GB 106330 (A) - Improvements in or relating to Submarine or Submersible Boats"
later registered at one of my old stomping grounds, the European Patent Office

The same principle was trialed at sea by the Italians in 1926 , Capt. Pericle Ferretti with H.3
(actually planned for production in the Sirena class but cut for cost)

The Dutch used first a simple pipe in early O class and a more complex design by Jan Jacob Wichers in 1938.

German schnorkel developed in 1933/34 for experimental 'fish boats'. So they had there own development.

 

[McPherson]

It attracts DEs only in a relative sense. They have to have a general idea of where the submarine already is in order to get close enough to pick up the submarine on sonar. Otherwise, a well-rafted diesel engine submarine sitting dozens or hundreds of miles from the nearest surface ship won't be picked up very easily by search sonar, which is usually where the submarine likes to be when recharging batteries- they prefer to look for enemy ships only when batteries are charged.

1. I believe the submarine has to come within effective torpedo range and execute a launch or it is just wasting fuel and man-hours.
2. The maximum that even a modern D/E can run on battery is about 150 hours at creep (1-2 m/s; ~4 knots, 600 nautical miles). Fast recharge takes anywhere from 4-10 hours depending on type battery and type electrical system (How much load it can handle.) AIP boats use a closed cycle engine to recharge, but it does nothing about creep speed or recharge times.
3. WW II boats have these same battery based limitations or worse. Their run time on lead acids at flank is measured in minutes and they are noisy, especially if they are twin screw and botched the screw blade geometry.
4. Sure they like fully charged batteries, but knowing 1-3, and knowing that a rafted diesel sub snorting cannot hide its pistons moving up and down or sending that noise through the bushings and shock mounts into the water to be detected by hydrophones within 10,000 meters offset through a North Atlantic noise channel above the thermocline means they start burning battery when they close to torpedo range. They are on a tight clock. About 1 hour for a Type 21. Battery goes below 40% after that and they are D.E.A.D. especially after Mr. Torpedo points back at them.

That's not how radar warning receivers work. The Type XXI in 1943 will be blind because Germany was technologically incapable of building centimetric radar warning receivers in a timely manner like I said, but any competently built submarine force (including late-war German submarines with proper radar warning receivers) can easily avoid LRMPs. The idea that Metox emissions were being homed in on by the Allies was misinformation and in reality they had no such ability to do that, and the late-war RWRs by Germany used crystal oscillators which produced no emissions anyway. A competently equipped diesel submarine has plenty of warning time to dive before a radar-equipped LRMP actually gets within range to spot the submarine. There's always the option of turning off the radar and having the LRMP scan for submarines visually, but we all know how useless that was in the war.

The German has to poke up something to see if there are aircraft close. I did not say RWR because RWR only tells you if there are propagators. To detect physical close proximity objects you have to use radar. Mr. Type 21 does not even dare stick up a snort (much larger than a radar mast), unless and until he clears skies. Emphasis on RADAR. And we have covered what happens to a detected D/E sub caught above the boundary layer of hot and cold water close to a convoy. It usually dies.

phx1138

I have a lot of respect for your expertise. But given their druthers, WW II submariners rather attacked on the surface and dive to escape. Earlier I wrote how the Germans were preparing to reinvent the submerged sonar only sound bearing attack. In principle, in WW II this means that they have to develop a base track and guesstimate the range via 1 or 2 methods:

a. acoustic interferometry which means they have to triangulate a sound source on at least six different bearings on their own base course and angle solve and plot intersecting scalars to get some idea of range and speed so they can maneuver to intercept and blind-fire a volley into the Predicted Intended Motion of the convoy. PH might be 5% and PK might be 3%. % you will be killed once your torpedoes start running? About 50% as the Allies trackback on your fish.

b. trust to blind luck that they know local acoustic weather and that their bearing only detection is at a set range gate sensitivity on the hydrophones that will allow them to launch on that bearing and their torpedoes' run times will carry into the noise blob and hit something. (The pre-war American method.) Chances of hitting anything with pattern runners? 0-2%. Chances with acoustics? 0-3%. Chances of getting killed? Same as with acoustic interferometry.

Given that I do not think the Germans after 1943 have a buffalo's chance in the midst of a Bill Cody hunting party, I do not see how the Type 21 achieves it's miraculous results.

Evidence? Falklands. German Type 209 Fumble McGurked an ideal setup with sitting ducks laid out for her. The British did not get her, either, but they roiled up the vicinity so hard that she could not re-acquire or set up again either.

IOW, the single sub stalk in open ocean did not work with a D/E boat. It has to be brown water ambuscade and that takes some luck.

 

[phx1138]

I have a lot of respect for your expertise.

I feel the same way. I also know you've a strong tendency not to be persuadable, one I share, so I don't want this to turn into a pissing contest.

I don't dispute the statistics, but IMO that's an ideal situation. I have to ask one question, based on OTL. If you're right, when the Type XXI appeared, why did the Brits, who knew this stuff better than both of us, seem to be in a panic over it?

Do I think even an earlier *Type XXI, in larger numbers, means German victory? As said, no. Neither do I think every encounter will look like the Tom Clancy novel outcome (if I can put it that way, with everything going just right for Allied ASW) it looks like you're offering.

If there was a TL where it went as you suggest, would I think it was outrageous? No. Am I biasing too much in favor of the boats? Maybe. The most likely outcome is probably between our POVs, IMO. So what does the writer want to accomplish? And is a stretch, one way or the other, too far in service of the goal?

But given their druthers, WW II submariners rather attacked on the surface and dive to escape.

How much of that is limitations of the equipment? Or the design decisions going into the boats? Or the basic technology? Even the USN fleet boats didn't have the udw speed or endurance to pursue convoys. The Type XXI was getting close to being able to--& that changes everything. It means you must have a/c on top. It's not just desirable, now. That wasn't always in place OTL. It also means you must have fast escorts. Most OTL convoys for the duration didn't.

Take away those things, you've left a convoy more/less defenseless... And if you add in pack attacks, you have a slaughter.

Something else nobody's considered yet (me included ): most sinkings for the duration weren't in convoy, they were single ships, sailing alone; some were "romping" ahead of convoys, some "lagging"--& either one makes them sub bait for Type XXIs, IMO, because you can't have air over every single ship in ATO. (Would it put the Queens at risk? No...not unless the sub was fairly extraordinarily lucky.)

Earlier I wrote how the Germans were preparing to reinvent the submerged sonar only sound bearing attack. In principle, in WW II this means that they have to develop a base track and guesstimate the range via 1 or 2 methods:

a. acoustic interferometry which means they have to triangulate a sound source on at least six different bearings on their own base course and angle solve and plot intersecting scalars to get some idea of range and speed so they can maneuver to intercept and blind-fire a volley into the Predicted Intended Motion of the convoy. PH might be 5% and PK might be 3%. % you will be killed once your torpedoes start running? About 50% as the Allies trackback on your fish.

b. trust to blind luck that they know local acoustic weather and that their bearing only detection is at a set range gate sensitivity on the hydrophones that will allow them to launch on that bearing and their torpedoes' run times will carry into the noise blob and hit something. (The pre-war American method.) Chances of hitting anything with pattern runners? 0-2%. Chances with acoustics? 0-3%. Chances of getting killed? Same as with acoustic interferometry.

Given that I do not think the Germans after 1943 have a buffalo's chance in the midst of a Bill Cody hunting party, I do not see how the Type 21 achieves it's miraculous results.

Evidence? Falklands. German Type 209 Fumble McGurked an ideal setup with sitting ducks laid out for her. The British did not get her, either, but they roiled up the vicinity so hard that she could not re-acquire or set up again either.

IOW, the single sub stalk in open ocean did not work with a D/E boat. It has to be brown water ambuscade and that takes some luck.

True. As stated, it makes me wonder how subs achieved any success at all--& that's (partly) why I think you're overstating the difficulty for the subs.

Was it easier for USN boats in PTO? It surely was, & that may be coloring my POV more than I realize. Either way, it just can't be so easy for ASW, either, or it wouldn't have been so damn hard to beat U-boats OTL.

 

[AlanJWhite]

German schnorkel developed in 1933/34 for experimental 'fish boats'. So they had there own development.

Sources please ...

because as far as I can find the Germans copied the Dutch boats they captured in '40
... and in any case initially planned to use it only for ventilation

See https://uboat.net/technical/schnorchel.htm a VERY PRO UB site and many others

 

[AJE]

1. I believe the submarine has to come within effective torpedo range and execute a launch or it is just wasting fuel and man-hours.
2. The maximum that even a modern D/E can run on battery is about 150 hours at creep (1-2 m/s; ~4 knots, 600 nautical miles). Fast recharge takes anywhere from 4-10 hours depending on type battery and type electrical system (How much load it can handle.) AIP boats use a closed cycle engine to recharge, but it does nothing about creep speed or recharge times.
3. WW II boats have these same battery based limitations or worse. Their run time on lead acids at flank is measured in minutes and they are noisy, especially if they are twin screw and botched the screw blade geometry.
4. Sure they like fully charged batteries, but knowing 1-3, and knowing that a rafted diesel sub snorting cannot hide its pistons moving up and down or sending that noise through the bushings and shock mounts into the water to be detected by hydrophones within 10,000 meters offset through a North Atlantic noise channel above the thermocline means they start burning battery when they close to torpedo range. They are on a tight clock. About 1 hour for a Type 21. Battery goes below 40% after that and they are D.E.A.D. especially after Mr. Torpedo points back at them.

In theory that would be the case but if all the submarine has to do is get beyond 10,000 meters (but let's say 25,000 meters so it has a good margin of error and can't be tracked on its immediately preceding course) from its target to be safe from hydrophones picking up the diesel noise then its batteries are easily capable of doing that.

The German has to poke up something to see if there are aircraft close. I did not say RWR because RWR only tells you if there are propagators. To detect physical close proximity objects you have to use radar. Mr. Type 21 does not even dare stick up a snort (much larger than a radar mast), unless and until he clears skies. Emphasis on RADAR. And we have covered what happens to a detected D/E sub caught above the boundary layer of hot and cold water close to a convoy. It usually dies.

Any close proximity object that isn't propagating is almost certainly no threat. The Allies tried to use visual searching from LRMP aircraft early on and U-boats evaded them without difficulty. If enemy search radar can be avoided by checking with the RWR there's no need to check for any non-radar-using vehicle with the submarine's own radar. Then the submarine won't give its position away.

a. acoustic interferometry which means they have to triangulate a sound source on at least six different bearings on their own base course and angle solve and plot intersecting scalars to get some idea of range and speed so they can maneuver to intercept and blind-fire a volley into the Predicted Intended Motion of the convoy. PH might be 5% and PK might be 3%.

More like 25% PK if a country has competitive torpedoes and sonar (and that wasn't even with the good US torpedo fire control computer).

 

[PSL]

Sources please ...

because as far as I can find the Germans copied the Dutch boats they captured in '40
... and in any case initially planned to use it only for ventilation

See https://uboat.net/technical/schnorchel.htm a VERY PRO UB site and many others

Rosslers THE UBOAT , generally considered the bible on the subject. What I was proposing was earlier development , Walters many proposals for U-Boat improvement were 'taken under advisement'. Had Furbringer been put in charge of U-Boat war , it would have been a very different war.

 

[pdf27]

The real kicker would be to adapt the submerged propeller speed to electric motor -not the diesel. It was estimated that "variable pitch propeller" geared to electric motor- not diesel RPM etc, should immediately increase top-speed of the plain Jane TYPE VII U-Boat from 7 to 12 knots submerged speed. Combined with above mentioned mods it should be able to hit 14-15 knots top speed for an hour or two, while 10 knots submerged could be possible for about 20 hours

The US fleet boats used their diesels purely as charging engines and so the propeller was always driven from the electric motor. The Germans could have done the same, but it would have led to a somewhat bigger submarine (and so fewer of them). Since their doctrine was for night surface attack (and their boats never really had time to change the design after radar killed that tactic), it's unlikely ever to be adopted.

The Type XXI in 1943 will be blind because Germany was technologically incapable of building centimetric radar warning receivers in a timely manner like I said, but any competently built submarine force (including late-war German submarines with proper radar warning receivers) can easily avoid LRMPs. The idea that Metox emissions were being homed in on by the Allies was misinformation and in reality they had no such ability to do that, and the late-war RWRs by Germany used crystal oscillators which produced no emissions anyway. A competently equipped diesel submarine has plenty of warning time to dive before a radar-equipped LRMP actually gets within range to spot the submarine. There's always the option of turning off the radar and having the LRMP scan for submarines visually, but we all know how useless that was in the war.

The key thing about Metox is that the idea it was detectable came from the interrogation of a shot down LRMP crewman - who told his interrogators that they found submarines by homing in on Metox. And the Germans believed him, spending vast amounts of effort in trying to cut down on any emissions from it without even looking for other types of radar. That shows a breathtaking level of incompetence on the part of the Germans.

And I come back, again, to the bigger question: where are the fast escorts coming from? Where are the diesels coming from? A million a/c engines proves nothing; the number of makers of marine diesels wasn't enormous, & the OTL production was short for the OTL demand...so what doesn't get built, to make up the difference? Are there other approaches than faster, bigger freighters? Are there other approaches to faster escorts than diesel DEs? (Turbines seem a non-starter; demand there is even greater, & number of producers even smaller.)

The OTL approach seems to have been planned as doing a Type 15/16 conversion on older fleet destroyers which had the required speed. You probably don't need high speed escorts for every role around the convoy - a handful for chasing down contacts once identified is probably enough.

In theory that would be the case but if all the submarine has to do is get beyond 10,000 meters (but let's say 25,000 meters so it has a good margin of error and can't be tracked on its immediately preceding course) from its target to be safe from hydrophones picking up the diesel noise then its batteries are easily capable of doing that.

As soon as it does that, the convoy is pretty much safe from re-attack: it's travelling at 6-9 kts along a defined course, so breaking contact on batteries is going to take a lot out of them. Flank speed with fresh batteries is 17 kts, so even for a fairly optimal course you're going to be at flank speed for an hour to get back in contact with the convoy. Per McPherson's numbers, that's enough to eat the entire battery pack and leave the boat practically dead in the water. Maybe enough to get back in contact with a 6 kt convoy (albeit with a depleted battery pack and so easy prey for escorts as it can no longer move fast), but a 9 kt convoy might well be able to simply sail away from it.

More like 25% PK if a country has competitive torpedoes and sonar (and that wasn't even with the good US torpedo fire control computer).

They had visual contact on that target (schnorkel), so probably used a visual range estimation - they are recorded as identifying what they saw as a periscope, so would know that they were pretty close.

 

[DougM]

Three questions that I think still need to be answered.
First how exactly does all this advancement happen for Germany with 0 advancement for the Allies? Unless this is a German wank?
How is Germany getting the resources to put it into production or are you cutting back the number of Subs to compensate ?
And the last question is does this decrease the transit time to and from the combat zones? If so how much? It seams to me Mostly it would just make it safer in transit vs very much faster.
The point of the last question is that the sub will take a give amount of time in transit and only carries so many torpedoes and some of those torpedoes will miss, some will be duds others will do limited damage and yet others they may not want to expend at the time of encounter if they are worried they will need them for later or whatever, the point is not 100% of torpedoes will sink a ship. So you have a maximum number of ships a sub can sink in a give amount of time. This is made worse by the amount of time needed for resupply and maintainance and crew R&R and such and the end result is a limited number of ships that can go to the bottom per German Sub.
So even if they somehow pull off this advancement much earlier then in the real world you still have a limit on how much more damage it can do.
Admittedly I don’t have access to these numbers right now but I would be really surprised if it resulted in all that many additional ships sunk. Yes it will be more. And you will have more subs around as they are harder to sink. But I don’t think it will approach the numbers needed to have a real effect given how fast the aliens built ships and other war supplies. Remember that by the mid part of the war the US was already turning its attention (as far as equipment and such goes) more and more towards the Pacific and cutting down on Europe so if these new subs come into play the US would most like only have to keep pumping supplies towards Europe a bit more.
But given the limitations of how long it takes to get a sub into combat range vs how many torpedoes it has I doubt this gets bad enough that the Spruce Goose is needed.
As for the British panic. At least part of that is undoubtedly the result of the typical fear of the unknown. In much the same way that every single new missile rocket or aircraft or ship or sub the USSR produced in the 50s- 80s was going to be the doom of the US.
Don’t get me wrong I am sure it would have been worse but not as bad as all that. And whenever the US manages to get everything going thier way like the Germans get with the subs it will have the bomb a year sooner and in number and will just nuke Germany

 

[phx1138]

The US fleet boats used their diesels purely as charging engines and so the propeller was always driven from the electric motor. The Germans could have done the same, but it would have led to a somewhat bigger submarine (and so fewer of them).

AIUI, the extra length for the geartrain wasn't excessive (something like 3' loa?), so it should affect numbers much.

The OTL approach seems to have been planned as doing a Type 15/16 conversion on older fleet destroyers which had the required speed. You probably don't need high speed escorts for every role around the convoy - a handful for chasing down contacts once identified is probably enough.

I guess I wonder "when". A lot of (early war only?) slow convoys had no DDs at all, or only 1. So when the conversions arrive, against when the *Type XXIs do, would seem to decide the ability to continue to run slow convoys at all.

As soon as it does that, the convoy is pretty much safe from re-attack: it's travelling at 6-9 kts along a defined course, so breaking contact on batteries is going to take a lot out of them. Flank speed with fresh batteries is 17 kts, so even for a fairly optimal course you're going to be at flank speed for an hour to get back in contact with the convoy. Per McPherson's numbers, that's enough to eat the entire battery pack and leave the boat practically dead in the water. Maybe enough to get back in contact with a 6 kt convoy (albeit with a depleted battery pack and so easy prey for escorts as it can no longer move fast), but a 9 kt convoy might well be able to simply sail away from it.

It won't have to run that far or hard from an escort that can't keep up. And when it's beyond the range of escort weapons, putting up the snort & charging battery, while trailing, would be pretty easy. Unless you've got TSRs or helos to continue to pursue & harass, which isn't (necessarily) a given in all cases: it would be once the *Type XXI threat is recognized, but that still leaves a large window.

One other thing (& this may be even more improbable): if the TSR/helo threat is so large, what are the odds of fitting *Type XXIs with SAR-homing SAMs? In that case, the radar mast isn't an a/c target--it's bait.

 

[pdf27]

AIUI, the extra length for the geartrain wasn't excessive (something like 3' loa?), so it should affect numbers much.

I suspect it might have been more of a weight than space issue - it's certainly not a huge issue, but every little helps.

I guess I wonder "when". A lot of (early war only?) slow convoys had no DDs at all, or only 1. So when the conversions arrive, against when the *Type XXIs do, would seem to decide the ability to continue to run slow convoys at all.

More a case of how much warning is available I suspect - the RN would have been in quite a good place against U-boats attacking submerged in 1939 I suspect, and any change in underwater performance would have been factored in. It was the lack of understanding of the potential for night surface attack which bit them as much as anything else AIUI.

It won't have to run that far or hard from an escort that can't keep up. And when it's beyond the range of escort weapons, putting up the snort & charging battery, while trailing, would be pretty easy. Unless you've got TSRs or helos to continue to pursue & harass, which isn't (necessarily) a given in all cases: it would be once the *Type XXI threat is recognized, but that still leaves a large window.

Breaking contact is really easy - you just hang there, ultimately. The problem is catching up again with a full charge - at 20,000 yards distance (10 nautical miles) against a 7 knot convoy, you have to close fast enough to eat your entire battery. That means while snorkelling (and hence deaf, etc.) you need to work your way around to the front of the convoy to have a chance of attacking again. In OTL, the U-boats could do that on the surface when the environment is permissive enough - I'm struggling a bit to see how that would be all that different with a snorkel.

One other thing (& this may be even more improbable): if the TSR/helo threat is so large, what are the odds of fitting *Type XXIs with SAR-homing SAMs? In that case, the radar mast isn't an a/c target--it's bait.

This has been looked at repeatedly in OTL (including all the U-flak boats). Problem is it makes the U-boat much worse at being a submarine while not being massively effective since aircraft are a lot cheaper than U-boats. Plus underwater-launch SAMs are a long way past the state of the art for WW2.

 

[PSL]

With large numbers of U-Boats , the Wolf Pact works well until 43 -when allied dominance of air restricts such activity to schnorkeling in the convoy vicinity , which restricts wolf pact sweeping rates. However since B-Dienst exploited Merchant code cracking through 1941-1944, they still had a good enough understanding of the WALLIE Convoy routes to place groups of U-Boats ahead of the convoy streams, allowing many opportunities attacks.

Generally convoy 're-attacks' were not recommended anyway due to the general convoy escort advantage- so submerged dashing ahead of convoy was not as crucial as might be imagined. With double the number of U-Boats at sea [due to schnorkling] they will still be an effective system to slow down WALLIE build up. If you look at the strategic tonnage flow to Europe , the overall Historical U-Boat war slowed the WALLIE progress by at least a year. Shifting U-Boat construction early in the war from type VII to type IX [& ignoring supply U-Boats] will result in less U-Boats built, but more U-Boats at sea through the war due to the much larger bunkerage [ better endurance] of the Type IX U-Boat.

The net gain sinking tonnage, through 1941 should be 6.4 million tons sunk compared to historical rates of 5 million tons sunk. The strategic result should push the WALLIE strategic build up back by 4-6 months in 1942. Continuing this rates through 1943, new AMERICA shipping should slow the Nazi gain but still slow the overall WALLIE logistical build up. Thus any gap should be narrowed to about 2 months through 1942/43. Continuing through 1944, this GAP could extend the delay in WALLIE LOGISTICAL build up to 3 months and 6 months by VE day. Clearly WALLIES are not going to tolerate that and further increase there ASW /MV building efforts can be expected.

BUT AT WHAT COST Mister SPOCK? AT WHAT COST?

 

[AJE]

The key thing about Metox is that the idea it was detectable came from the interrogation of a shot down LRMP crewman - who told his interrogators that they found submarines by homing in on Metox. And the Germans believed him, spending vast amounts of effort in trying to cut down on any emissions from it without even looking for other types of radar. That shows a breathtaking level of incompetence on the part of the Germans.

That's because the Germans didn't believe centimetric radar was possible, as Hitler had refused requests for their scientists to develop magnetrons further and their existing projects had not yielded useful microwave sources (much like the British prior to the invention of a useful cavity magnetron). But once the aircraft with H2S crashed, they were working on countering centimetric radar as much as anyone would, it's just that they believed Metox was being tracked as well and there were serious technical difficulties in developing a centimetric RWR, which the Luftwaffe night fighters had priority on anyway.

As soon as it does that, the convoy is pretty much safe from re-attack: it's travelling at 6-9 kts along a defined course, so breaking contact on batteries is going to take a lot out of them. Flank speed with fresh batteries is 17 kts, so even for a fairly optimal course you're going to be at flank speed for an hour to get back in contact with the convoy. Per McPherson's numbers, that's enough to eat the entire battery pack and leave the boat practically dead in the water. Maybe enough to get back in contact with a 6 kt convoy (albeit with a depleted battery pack and so easy prey for escorts as it can no longer move fast), but a 9 kt convoy might well be able to simply sail away from it.

That's assuming the convoy has to be attacked from underwater the next time, escorts tended to be targeted if possible. If all 8 or so escorts are torpedoed and destroyed the convoy can be attacked while on diesel power on the surface. Otherwise the submarine can go around the convoy on the surface and position itself in front for the convoy to run into it again.

 

[McPherson]

I feel the same way. I also know you've a strong tendency not to be persuadable, one I share, so I don't want this to turn into a pissing contest.

Right back at you, so let me stick to what I understand and remind everyone, it is my opinion only and it is not gospel or personal EVER. Others can be right and I can be wrong, ya know?

I don't dispute the statistics, but IMO that's an ideal situation. I have to ask one question, based on OTL. If you're right, when the Type XXI appeared, why did the Brits, who knew this stuff better than both of us, seem to be in a panic over it?

a. Maybe they are not as technically aware of snort boat limitations as we are today. That is one possibility.
b. Morale. They thought they had the U-boat problem licked and then here come the Germans with this new U-boat that they may not be able to solve quickly. They had some funk over the V-1 and V-2 because of how hard it was to deal with these weapons in the short term morale wise. Of course the military professionals could crank through the numbers and see that these wonder weapons were endurable and the Germans were doomed to fall to either the Russians on the ground or the Allied bomber offensive in 1945, if the Normandy landing had to be delayed, but tell that to someone whose home has been V-2ed. The politicians would not understand either (Exception Churchill who at least had competent scientific advisors.). Morale in war leads to some incredibly stupid military decisions (Market Garden was in part about V-2 launch sites.), so I agree that the RN in a panic might have abandoned convoy. The USN and Canada though would NOT.

Do I think even an earlier *Type XXI, in larger numbers, means German victory? As said, no. Neither do I think every encounter will look like the Tom Clancy novel outcome (if I can put it that way, with everything going just right for Allied ASW) it looks like you're offering.

I'm a numbers man and I also have a good idea of what the USN is up to at this time. A huge amount of US research is in ASW and counter submarine operations and this starts to show in 1944. The Germans by 1944 are rank amateurs compared to what the Allies are doing, because the British have not let up on the ASW research either. It is an offense defense race the allies will win easily until true submarines and long range fire and forget heavyweight torpedoes come into service. 1955 is that tilt year.

If there was a TL where it went as you suggest, would I think it was outrageous? No. Am I biasing too much in favor of the boats? Maybe. The most likely outcome is probably between our POVs, IMO. So what does the writer want to accomplish? And is a stretch, one way or the other, too far in service of the goal?

Just have to read this to see what I think. ...Those Marvelous Tin Fish: The Great Torpedo Scandal Avoided.

How much of that is limitations of the equipment? Or the design decisions going into the boats? Or the basic technology? Even the USN fleet boats didn't have the udw speed or endurance to pursue convoys. The Type XXI was getting close to being able to--& that changes everything. It means you must have a/c on top. It's not just desirable, now. That wasn't always in place OTL. It also means you must have fast escorts. Most OTL convoys for the duration didn't.

"Mr. Sikorsky can your helicopter dip a sonar and will it drop bombs?"

"Give me six months."

"Mr. Kaiser, we need more C-hulls modified."

"Give me three months."

Take away those things, you've left a convoy more/less defenseless... And if you add in pack attacks, you have a slaughter.

The Type 21 cannot attack in packs. It does not have the unimpeded communications of the early war U-boat.

Something else nobody's considered yet (me included ): most sinkings for the duration weren't in convoy, they were single ships, sailing alone; some were "romping" ahead of convoys, some "lagging"--& either one makes them sub bait for Type XXIs, IMO, because you can't have air over every single ship in ATO. (Would it put the Queens at risk? No...not unless the sub was fairly extraordinarily lucky.)

Here I agree. Corral those rompers. CONVOY everybody.

True. As stated, it makes me wonder how subs achieved any success at all--& that's (partly) why I think you're overstating the difficulty for the subs.

I have to confess, I wargamed it for the storyline to see average results. If the subs try the tactics I postulated against a 1944 Allied convoy they will hardly hit anything by the torpedoes of the day. The periscope attack is about the only way to get efficient torpedo hits (about 25%) and by 1944 it is almost suicide.

Was it easier for USN boats in PTO? It surely was, & that may be coloring my POV more than I realize. Either way, it just can't be so easy for ASW, either, or it wouldn't have been so damn hard to beat U-boats OTL.

Entirely different war from the North Atlantic. Sensor density was far less and terrain far worse. Different tactics.