WI:Krigesmarine type xxI

[Astrodragon]

1. Above 12 knots semi-submerged your snort is damaged and rendered useless. British experiments proved this as early as 1920. This is still true for modern boats.
2. Conversion of the sail is not enough. Need to streamline the hull case and that would take more than a year. How do I know this? Because the US DID IT. Called GUPPY.
3. It was retracted, that snort. That V-80 boat made battery and Navol powered runs and never broke 19 knots EVER.
4. At 10 knots you make a noise target a deaf moose can hear with an ear trumpet. The sub is also deaf itself with the GSF gear the Germans used. By 1943 the allies had sonobuoys and chase weapons. Might be difficult to depth charge from a destroyer, but a snort boat is dead meat to FIDO. Diesels submerged put 8x as much noise into the water. This increases air to surface kills 2x.
5. What 4 times as many attacks? Nothing has changed the log function or the cube law when it comes to convoy.

I would add..

At higher speeds, your snort leaves a plume even the RAF can see a LONG way away. Its not to be used as an attack tool.
The idea of a slow speed motor to allow days underwater - we assume the crew have given up on breathing?
The streamlining problem is FAR more than replacing the conning tower with a sail - the biggest saving is streamlining the hull and fittings. Problem is, the more you do that, the longer the boat takes to dive. Might not be a good exchange when that Wellington is bearing down on you...

 

[Astrodragon]

Germans were producing about 286 uboats a year in 1943, so we are assuming here max about that number of XXI.

Those figures are actually very dodgy. They seem to include quite a few Type 21's, which certainly were not complete and working in 1943.
Never trust German Ww2 production figures...

 

[McPherson]

At higher speeds, your snort leaves a plume even the RAF can see a LONG way away. Its not to be used as an attack tool.

Thanks. I forgot to mention it. I am sort of like;

for not mentioning that very obvious drawback.

The idea of a slow speed motor to allow days underwater - we assume the crew have given up on breathing?

Or carbon monoxide poisoning or slow bends or about a dozen other respiratory problems?

The streamlining problem is FAR more than replacing the conning tower with a sail - the biggest saving is streamlining the hull and fittings. Problem is, the more you do that, the longer the boat takes to dive. Might not be a good exchange when that Wellington is bearing down on you...

Agreed.

P.S. While modern AIP boats can stay under for up to 10 days at creep (3 m/s), this is no guarantee that they will have battery reserve to assume tactically useful speed unless a convoy or a target surface vessel runs toward them and practically runs over them. All of those stories in wargames about US carriers stumbling into diesel electric boats? This is because the carriers cut circles in the water where the diesel boats were known to be. The stalk is easy when the prey sort of sits there and dares you to creep up on it. In combat, things are a lot dicier.

Our closest example to this is the Falklands War. HMS Conqueror had a devil of a time getting into position (with satellite recon bird help no less) and she had trouble with her fish besides. When she sank the Phoenix, it was with classical WW II methods and WW II weapons using her nuclear boat propulsion to give her the necessary tactical speed to arrange the merge for the final set up and war-shots.

The problems an AIP boat or a snort boat has in the modern stalk are no different than a standard diesel electric in 1944. It has to find an ambush spot and lie in wait for the target to come to it. All of the elements that come into play for an ambush weapon are the classic diesel electric boat problems. Once the enemy looks at a map and figures out where the boat has to hide to attack as an ambush weapon, the jig is up. H/K assets, rerouting, constant LRMPs to keep snorts down... Sound familiar? British ASW tactics that worked in WW II, still work today, except against nuclear powered boats. THAT is why first class navies accept the attendant pump noise and expense of the nuclear power plants in a sub. The power reserve is for electric gills, air plant and tactical speed.

IOW the type 21 becomes just another slow German U-boat now operating in the brown water zone with no useful blue water capability at all to affect the Battle of the Atlantic.

It seems to be something of a classic mistake that wonder weapon exponents overlook to see how the wonder weapon actually works in the existing wartime mix. In the air, the example is the Me-262. How does a jet fighter stop 4-6 million very angry Russians?

 

[Cryhavoc101]

I thought that the Snorkle would start to deform and be damaged above 5 knots?

 

[McPherson]

I thought that the Snorkle would start to deform and be damaged above 5 knots?

Not modern types. The tactical limit for periscope shears is about 5 m/s. Not even carbon buckey-balls can handle that.

 

[Cryhavoc101]

Not modern types. The tactical limit for periscope shears is about 5 m/s. Not even carbon buckey-balls can handle that.

So a modern periscope cannot operate above 10 knots so I therefore assume that a 1940s first Gen Snorkle is likely only intended for speeds not much above steerage 2 to 3 m/s (which has always been my understanding).

The reason I mention it is because I get the impression that some posters beleive that a snorkle allows a given sub to travel at its maximum 'surfaced' speed while at periscope depth while its actual intention is to make it far harder to detect from the air while allowing it to recharge its batteries.

 

[McPherson]

So a modern periscope cannot operate above 10 knots so I therefore assume that a 1940s first Gen Snorkle is likely only intended for speeds not much above steerage 2 to 3 m/s (which has always been my understanding).

The reason I mention it is because I get the impression that some posters believe that a snorkel allows a given sub to travel at its maximum 'surfaced' speed while at periscope depth while its actual intention is to make it far harder to detect from the air while allowing it to recharge its batteries.

I don't know where people get the idea that one can move what is essentially a tall hollow pipe (periscope or snort) through water at 30 knots. Now with stoutly made non-penetrating sensor masts or modern snorts where the shear can be engineered to a more v-shape and can be somewhat bladed better you can reach about 10-12 knots; but you still have what is essentially a tall pipe despite best materials and design. It will snap under load.

 

[AJE]

I don't know where people get the idea that one can move what is essentially a tall hollow pipe (periscope or snort) through water at 30 knots. Now with stoutly made non-penetrating sensor masts or modern snorts where the shear can be engineered to a more v-shape and can be somewhat bladed better you can reach about 10-12 knots; but you still have what is essentially a tall pipe despite best materials and design. It will snap under load.

Hollow hydrofoil blades operate at many times that speed.

 

[McPherson]

Hollow hydrofoil blades operate at many times that speed.

They are planes and not in the vertical (Y axis) against the water column, nor are they ever at depth below 5-7 meters before they plane. Makes a HUGE difference.

 

[thaddeus]

noticed that the battery cells tripled for Type XXI (over Type VII) whereas the smaller Type XXIII required the same number as earlier coastal boat Type II (68), this being a very casual reading of the specs.

IF the Type XXI starting having an outsized impact in 1943 - 1944, wouldn't the battery factory become target number one for bombing? there was only one until 1944?

understand the rationale for increased underwater range and hence (likely) need for more batteries but why create for themselves another scarcity or bottleneck?

 

[PSL]

Rossler reported about a fixed schnorkel experimental sub at end of the war. This was designed for 17 knots submerged, but it would be nearly silent at 6 knots. The design project was called "Tummler" based on a coastal U-Boat model, but the war ended before anything could be done. it would have had stability problems but not likely much more than the "winter garden" imposed on late war fleet.

The actual U-Boat programme developed a fast schnorkel that was fitted on two boats at the end of the war named Oelfken able to manage 10-11 knots , but none were deployed B4 the end of the war.

Creep motors were standard fit on Type XXI & XXIII plus most post war U-Boats [limp home capability].

 

[PSL]

noticed that the battery cells tripled for Type XXI (over Type VII) whereas the smaller Type XXIII required the same number as earlier coastal boat Type II (68), this being a very casual reading of the specs.

IF the Type XXI starting having an outsized impact in 1943 - 1944, wouldn't the battery factory become target number one for bombing? there was only one until 1944?

understand the rationale for increased underwater range and hence (likely) need for more batteries but why create for themselves another scarcity or bottleneck?

Increasing sub speed due to streamlining is independent of battery consumption which is another reason why staying with squeezing more out of Type-VII & IX is a wiser route.

 

[McPherson]

Rossler reported about a fixed schnorkel experimental sub at end of the war. This was designed for 17 knots submerged, but it would be nearly silent at 6 knots. The design project was called "Tummler" based on a coastal U-Boat model, but the war ended before anything could be done. it would have had stability problems but not likely much more than the "winter garden" imposed on late war fleet.

The actual U-Boat programme developed a fast schnorkel that was fitted on two boats at the end of the war named Oelfken able to manage 10-11 knots , but none were deployed B4 the end of the war.

Creep motors were standard fit on Type XXI & XXIII plus most post war U-Boats [limp home capability].

Type XXII. Complete program failure.

Increasing sub speed due to streamlining is independent of battery consumption which is another reason why staying with squeezing more out of Type-VII & IX is a wiser route.

Why? The boats were dead ends with numerous design flaws. If you are going to try new tech, fresh sheet the design to fix your known problems in your old boats.

 

[thaddeus]

noticed that the battery cells tripled for Type XXI (over Type VII) whereas the smaller Type XXIII required the same number as earlier coastal boat Type II (68), this being a very casual reading of the specs.

IF the Type XXI starting having an outsized impact in 1943 - 1944, wouldn't the battery factory become target number one for bombing? there was only one until 1944?

understand the rationale for increased underwater range and hence (likely) need for more batteries but why create for themselves another scarcity or bottleneck?

Increasing sub speed due to streamlining is independent of battery consumption which is another reason why staying with squeezing more out of Type-VII & IX is a wiser route.

that was my implication to have evolution of the Type VII and/or build smaller Type XXIII

Rossler reported about a fixed schnorkel experimental sub at end of the war. This was designed for 17 knots submerged, but it would be nearly silent at 6 knots. The design project was called "Tummler" based on a coastal U-Boat model, but the war ended before anything could be done. it would have had stability problems but not likely much more than the "winter garden" imposed on late war fleet.

The actual U-Boat programme developed a fast schnorkel that was fitted on two boats at the end of the war named Oelfken able to manage 10-11 knots , but none were deployed B4 the end of the war.

Creep motors were standard fit on Type XXI & XXIII plus most post war U-Boats [limp home capability].

(from complete layman's viewpoint) why did they scheme a closed circuit diesel system which projected to carry 9 1/2 tons of liquid oxygen rather than small scale project to perhaps power a creep motor or recharge batteries?

of course, never understand the years spent on hydrogen peroxide projects, except possibly for torpedoes?

 

[McPherson]

(from complete layman's viewpoint) why did they scheme a closed circuit diesel system which projected to carry 9 1/2 tons of liquid oxygen rather than small scale project to perhaps power a creep motor or recharge batteries?

of course, never understand the years spent on hydrogen peroxide projects, except possibly for torpedoes?

KABOOM. This also plagued Japanese type 93 torpedoes. They, the Germans, did not really understand what they were up against. At least, the Japanese knew how dangerous oxygen and OIL contaminants, were.

Navol is safer, but not by much.

 

[PSL]

that was my implication to have evolution of the Type VII and/or build smaller Type XXIII



(from complete layman's viewpoint) why did they scheme a closed circuit diesel system which projected to carry 9 1/2 tons of liquid oxygen rather than small scale project to perhaps power a creep motor or recharge batteries?

of course, never understand the years spent on hydrogen peroxide projects, except possibly for torpedoes?

Leafing through Rosslers book there must be 20-25 projects for New U-Boats from 1943-45 plus another 5-10 mini sub designs examined.

Simple answer was no one was going to reject XXI & XXIII -for an over haul of the existing fleet -after selling the XXI & XXIII as wunderwaffen. The more complex answer was that "squeezing " more out of existing U-Boat fleet would have neutralised the WALLIE ASW threat , but would do nothing to reclaim the high MV kill rates of 1st half of the war. So the increased KM effort could only offset allied late war ASW efforts resulting in same MV loss tonnage at the cost of much higher U-Boat loss rate. In other words just a less slippery slope.

What the XXI/XXIII really offered was a new U-Boat warfare that spent most of its time hunting convoys underwater with long range GHG sonars and using MF-ASDIC underwater to spot MV and launch torpedoes underwater...with little idea off results. The wolf pack system for sweeping vast areas of ocean would have to be replaced with a fleet of schnorkeling 'lone wolfs'.

Now if LW worked hand in glove with KM, they could have built a fleet of long range 4 engine maritime patrol bombers. To search for WALLIE convoys and broadcast those locations to schnorkeling subs near by. But that would also work for a fleet of schnorkel equipped TYPE-IX U-Boats with NAXOS RWR etc.

 

[bernardz]

Those figures are actually very dodgy. They seem to include quite a few Type 21's, which certainly were not complete and working in 1943.
Never trust German Ww2 production figures...

Fair enough, let use it then as a first level approximation for the XXI.

The other issue is timing.

https://uboat.net/technical/electroboats2.htm

November 1942 the idea is born
End of January 1943 detailed theoretical calculations were finished
End of June 1943 a preliminary design was completed.
Presented to Hitler the 8th July 1943 for production
13th August 1943 an order was given for the transition to building Electroboats.
Scheduled prototypes in November 1944
Regular production boats would be ready for operational use in 1946.

Note: I know that here that I am deviating from the OTL because in the OTL the XXI were rushed.

So basically we are looking assuming normal development of a 4 to 5-year development cycle.

If these boats were to start in 1943 coming off the production line in mass then this POD has to start in early 1939. Would the Germans be willing in 1939 when they are trying desperately to get VII out? What would be more likely is that the VII would be modified to have a bigger battery, as there was nothing wrong in 1939 with the technology of the VII so I doubt the XXI in this POD would be as good as the XXI in the OTL.

Also, why would the development team think they need to put in a schnorkel something that only was seen as useful in 1943 and took about a year to be developed and go into mass use in 1944. So I doubt that the Schnorkel would be put into the uboats built in 1943. The XXI in 1943 in this POD would not have a Schnorkel

 

[eltf177]

Honestly I don't think the Walther system could have enough of the bugs worked out of it to make it operational. Not to mention supplying the hydrogen peroxide, which was also needed for the Me-163 "Komet" and other rocket projects...

 

[Astrodragon]

Personally I wouldnt want to be sitting in a tube full of Hydrogen Peroxide being depth charged.
The stuff has a nasty tendency to dissasociate if you look at it funny, let alone let off big bangs closeby.

 

[thaddeus]

that was my implication to have evolution of the Type VII and/or build smaller Type XXIII

(from complete layman's viewpoint) why did they scheme a closed circuit diesel system which projected to carry 9 1/2 tons of liquid oxygen rather than small scale project to perhaps power a creep motor or recharge batteries?

of course, never understand the years spent on hydrogen peroxide projects, except possibly for torpedoes?

Leafing through Rosslers book there must be 20-25 projects for New U-Boats from 1943-45 plus another 5-10 mini sub designs examined.

Simple answer was no one was going to reject XXI & XXIII -for an over haul of the existing fleet -after selling the XXI & XXIII as wunderwaffen. The more complex answer was that "squeezing " more out of existing U-Boat fleet would have neutralised the WALLIE ASW threat , but would do nothing to reclaim the high MV kill rates of 1st half of the war. So the increased KM effort could only offset allied late war ASW efforts resulting in same MV loss tonnage at the cost of much higher U-Boat loss rate. In other words just a less slippery slope.

What the XXI/XXIII really offered was a new U-Boat warfare that spent most of its time hunting convoys underwater with long range GHG sonars and using MF-ASDIC underwater to spot MV and launch torpedoes underwater...with little idea off results. The wolf pack system for sweeping vast areas of ocean would have to be replaced with a fleet of schnorkeling 'lone wolfs'.

Now if LW worked hand in glove with KM, they could have built a fleet of long range 4 engine maritime patrol bombers. To search for WALLIE convoys and broadcast those locations to schnorkeling subs near by. But that would also work for a fleet of schnorkel equipped TYPE-IX U-Boats with NAXOS RWR etc.

yes, "shiny new object" was ascendant.

the logic behind my scenario of building the smaller Elektroboot (first) was easier to build (or at least faster), they used much less batteries, and at least some cooperation with LW possible (as they are operating near coast)

with the enhanced snorkel u-boats attempting the long range "lone wolf" attacks.

seems like there would have been enough reason to revamp their near constant messaging by then? @McPherson suggested messaging buoys (IIRC, cannot find exact post)