"Bastard" Electro U-boats From Early 1943?

[Karwats]

Hi Guys

Here is a link to a very nice plan drawing of a VII C/41.
http://www.mikekemble.com/ww2/images/typeVIIC.jpg

Link kindly provided by Red devil.

The drawing again highlights some of the problems of space.

As I suspected the underdeck space below the fwd torpedo storage is not only utilised for storing torpedoes. You will notice a large tank under the fish-possibly freshwater or trim tanks. So if we fit batteries here we need to move the tank.

You will alo see that the KM have started to streamline the hull allready: no deck gun and removing the net cutter up fwd. Now it sould be a fairly simple solution to just remove the various AA weapons from the rear of the tower,this will streamline allready. Bear in mind the conning tower - or fin is essentially there as a housing for the various masts and doesnt really need any structural strength it is essentially the same as a motorbike fairing and does the same job. I think streamlining the hull is not so much a structural problem of rebuilding the hull,but more removing all the various appendages and portrusions sticking out and creating drag.
Very little if any rebuilding would need to be done.

Moving to the aft torpedodo room,our space problem is indeed more pronounced. The deck indicated in the picture is in fact the pressure hull,so no underdeck storage.That being said if you accept that you have no offensive capability aft,the torpedo storage and tube can be removed so the whole compartment could become a battery in itself-not sure how many you could store in that space though. Again, adding a few tons of weight right on the stern of the boat is going to make trimming a nightmare.

Antoher problem is the generators-they are designed to charge the current batteries of the boat,increasing the battery by approx 1/3 will obviously also increase the charging rate. So it would be advisable to look at more powerful generators. I don't see fitting new e-motors as a necesity. Firstly you should be able to increase underwater speed by streamiling the hull. That being said increasing underwater speed is the least of our problems. As using maximum speed underwater is hell on the battery figure about 45 min at maximum speed. Bear in mind even modern diesel boats blow their batter in 2-4 hours at max speed. So we need endurance more than anything else.

On another tack,what was the technical expertise of the KM in producing batteries. That is can or could they produce cells that were more powerfull but utilising the same housings. Does anyone know if the cells used in the XXI's were the same as those in the VII's, we might solve our problem with little or no rebuilding if we could get more power from the same amount of cells.As an indication we achieved a nearly 40% increase in battery power on the Daphne' class back in the '90's by doing exactly this.

[Mark V]

Streamlining the hull plus conning tower, and dispensing deck gun is easiest way of improving underwater performance.
Mark V

Just how easy is "the easiest way"? What Mark V and Karwats suggest sounds interesting. At the same time however, I must admit it sound like such a radical rebuilding of the U-boats that it may not be worth the effort. How would you suggest to streamline these things? Streamlining the hull plus the conning tower of the VIIs and the IXs will take months in the shipyards. Wouldn´t a completely new conning tower and a new exterior hull be needed?

Hi,

I think there is nothing radical on dispensing deck gun, smoothening the contours of conning tower, eliminating the rails, wire-cutters, and everything protruding from the weather deck.

Mark V

[Lkefct]

http://www.globalsecurity.org/military/ ... /guppy.htm

My understanding of what the US navy did was to convert their old fleet type of boats, as a stop gap before the nuclear navy could be developed. The extrenal hull of a uboat is not nearly as substantial as the pressure hull underneath. A lot of what is visible is very light wieght steel. Modifications can be made to that relatively quickly, possibly even as part of a regular refit. Fitting and producing new engines, and more batteries is a more substaila problem, but not impossible with any descent engineering work.

the biggest issue I have with early electro boats is that there is no way to fire the torpedos except to come up close to the surface. the Type XXI intended to use FAT and Lutz torpedos fired from the hydrophone cotacts so that they where not as close to the surface. I takes depth charges, hedgehog, and other bombs a long time to get to a Uboat depth. At creeping speeds, an old style Uboat can't go very far, even if it takes a minute or so to get to 100 meters. But a type XXI is going to move many times further, so if they hear the bombs going into the water, and take immediate evasive action, the bombs are likely to miss. That is the advantage. It also allows the boats to retain some initative and keep becoming actively involved in hunting targets so long as they can move at 10-12 knots. A submerged VII or IX is only 6-7 knots, and thus as slow as the convoy forward progress.

[Lars]

My understanding of what the US navy did was to convert their old fleet type of boats, as a stop gap before the nuclear navy could be developed. The extrenal hull of a uboat is not nearly as substantial as the pressure hull underneath. A lot of what is visible is very light wieght steel. Modifications can be made to that relatively quickly, possibly even as part of a regular refit. Fitting and producing new engines, and more batteries is a more substaila problem, but not impossible with any descent engineering work.

Karwats, Mark V, Lkefct, Tim, Tony and others,

Very interesting comments all around. Ausgezeichnet, Männer

It seems I was wrong about streamlining the conning tower and the exterior hull. The conning tower could be streamlined simply by removing things sticking out from it, like the Flak guns. Regarding the hulls, as several point out, it´s the pressure hull which is the delicate one. It´s much easier - meaning much faster - to improve the exterior hull and make it more streamlined.

Allow me to conlude:
The Electroboat idea was born in November 1942. If a stop gap solution of improving the existing U-boats had been decided, it would certainly have been possible. Six months later, by May 1943, the first improved VIIs and IXs could have been ready with improved streamlining of the conning tower and the exterior hull. Removal of the deck gun and the weight from its shells would help too. More battery-power would have been possible by changes to the aft torpedo-room and the removal of four of the 24 torpedos. Bigger electro motors is a better solution than simply adding two auxiliary electro motors to the existing motor.

Not all these changes would have been possible or desirable.

However, I believe that enough changes would be possible to allow a 50% increase in underwater speed and endurance. The dived VIIs and IXs would be faster and more silent. Bad news for the Allied ASW.

The great nit would be, that improved streamlining may hurt the surface speed. The streamlined XXI was actually slower on the surface than below water. IMO, the improvements of the VIIs and XIs would have to be done so that surfaced speed wasn´t affected and improved if possible.

Any comments?

[Lars]

I read some of the highly recommendable book "Geschichte des deutschen U-bootbaus" (History of the German U-boat building"), by Eberhart Rössler yesterday.

It turns out that the Germans took the very opposite direction regarding the conning tower than suggested in this thread. In November 1942, the Germans decided that more and better flak guns was the answer to the increased Allied air power at sea. Four series of elaborate rebuilding of the conning towers of existing u-boats followed, the first rebuilt u-boat being ready the next month, in December 1942.

These rebilings had almost no benefits whatsoever as the best solution for a u-boat still was to dive as fast as possible when an aircraft showed up. The Germans kept rebuilding the u-boats right up till the last months of the war.

Rössler remarks that the rebuilded but less streamlined conning towers had a serious negative effect on the u-boats submerged performance! It seems we were right about removing the deck gun and the conning tower flak guns for better underwater performance

[Karwats]

It turns out that the Germans took the very opposite direction regarding the conning tower than suggested in this thread. In November 1942, the Germans decided that more and better flak guns was the answer to the increased Allied air power at sea. Four series of elaborate rebuilding of the conning towers of existing u-boats followed, the first rebuilt u-boat being ready the next month, in December 1942.

This I think illustrates their mistaken tactical use of boats as submersibles, i.e long periods of surface running and diving for short periods. As opposed to the other way around. Even with boats snorting for long periods of time,I think they would heven been basically invulnerable from airborne radar-40's vintage- detection. This would drastically decrase U-boat losses and in any case it is alot easier to dive and evade while allready at periscope depth than from the surface.

[Mark V]

It turns out that the Germans took the very opposite direction regarding the conning tower than suggested in this thread. In November 1942, the Germans decided that more and better flak guns was the answer to the increased Allied air power at sea. Four series of elaborate rebuilding of the conning towers of existing u-boats followed, the first rebuilt u-boat being ready the next month, in December 1942.

This I think illustrates their mistaken tactical use of boats as submersibles, i.e long periods of surface running and diving for short periods. As opposed to the other way around.

An mistake definately. Admittedly Germans were short of short-term measures before boats could be fitted with snort-masts. Shortsightedness on their part that countermeasures against improved radars and increasing patrol aircraft numbers and ranges were not developed seriously much earlierly.

Not that flak-boats helped in any way. I guess it was more to give "something" to boat crews when sending them to nearly assured destruction.

Even with boats snorting for long periods of time,I think they would heven been basically invulnerable from airborne radar-40's vintage- detection.

True, only AN/APS-20 had any kind of meaningful detection range against snorting submarine - but that radar, though WW2 era invention - was only just coming to limited service at the time when war ended - for AEW. It was big mutha, but it could had been be carried by 4-engined maritime aircrafts same time as armament.

Upgrading radars of ASW aircrafts from H2S "family" to AN/APS-20 would had taken couple years, would had made older aircraft types obsolete in ASW, limited the weapon load and/or range of even the most modern ac types, and seriously complicated escort carrier operations - need of separate "hunter" and "killer" aircraft (that route was followed for some time in late 40s and 50s in anticipation of Soviet XXI clones...).

Regards, Mark V

[Lars]

only AN/APS-20 had any kind of meaningful detection range against snorting submarine - but that radar, though WW2 era invention - was only just coming to limited service at the time when war ended - for AEW. It was big mutha, but it could had been be carried by 4-engined maritime aircrafts same time as armament.

Upgrading radars of ASW aircrafts from H2S "family" to AN/APS-20 would had taken couple years, would had made older aircraft types obsolete in ASW, limited the weapon load and/or range of even the most modern ac types, and seriously complicated escort carrier operations - need of separate "hunter" and "killer" aircraft (that route was followed for some time in late 40s and 50s in anticipation of Soviet XXI clones...).

Regards, Mark V

Good points by Mark V and Karwats.

It took a long time for the schnorkel to appear though the need seems obvious. In a conference with Dönitz on March 13th 1943, professor Walter (the man with the sci-fi Walter-boats) mentions the schnorkel-idea as a response to Allied air power. Dönitz imidiately grabs the idea, but it takes a fully 11 months before the first frontboot sails out on a mission with schnorkel on February 19th 1944! Fitting the U-boat fleet with schnorkels continued at a leisury pace even then.

But how much good would a schnorkel fitted U-boat fleet do in the battle of the Atlantic anyway. It would slash lossed caused from aircrafts but it would also cut the u-boats speed in half. Schnorkel fitted U-boats in the Atlantic would be better than non-snorkeling u-boats but the schnorkel had a heavy pricetag in mobility, right?

Allied air-borne AN/APS-20 radar: The Germans developed a radar-absorbing paint called "Schornsteinfeiger" (chimney sweeper). Some schnorkel heads were painted with this paint which absorbed radar at 10 cm wave-lenght, but not Allied radar at 3 cm wave-lenght which the Germans were initially not aware of. The points is however, that radar absorbing paint was a part of the German inventory and that it could have been developed further had the war continued beyond May 1945, making Allied air-borne radar detection more difficult.

[Karwats]

It would slash lossed caused from aircrafts but it would also cut the u-boats speed in half. Schnorkel fitted U-boats in the Atlantic would be better than non-snorkeling u-boats but the schnorkel had a heavy pricetag in mobility, right?

Well once the boats had been "cleanup -up" externally you could prbably expect quite a significant increase in submerged speed- I'm mot too hot on flow dynamics-but lets say 10 knots (30%) increase fro arguments sake.So yuor transit speed is not reduced that much. But your survivability rate goes up by 60%-again for arguments sake. Longer transit times comes a very distant second in this scenario. Keep in mind while snorting the boat can proceed at full tilt while not draining the battery.

Yet again we come back to incorrect use of u-boats. In the final analysis surface speed should be largely irrelevant and submerged speed paramount for transits.

On the subject on the 3-10 cm radars. Once the change in thinking to submerged operations and the realisation that radar was the primary means of detection, the developement of RWR -Radar Warning Receivers-would proceed apace. The Luftwaffe Nachtjägers were developing them in any case for night fighting. Also in any active/passive range contest, the passive system be it radar or sonar, normally has a 10-20% range advantage on detection,sometime a hell of a lot more on passive sonar . So once the RWR's were fitted on the snortheads or search periscopes-the allies would more than likely never detect a snorting boat, as the boat would have radar warning long before its snortmast came into detection range.

Of course the visual detection possiblity is still there,but it is pretty damn hard to spot a mast unless you happen to be right on top of it.

[red devil]

http://www.uboat.net/fates/scuttled_xxi.htm - electro boats (scuttled, pictures).

[Lars]

An Amazing entry from someone called esl over at Alternate History Forum. Get him over here!

Esl imagines two retrofitted VIIC-types as alternative to the XXI, a 1942- model and a 1944-model.
1942-model: A streamlined tower with schnorkel, 10 torpedoes instead of 14, no guns, remove the bottom torpedo row and place extra batteries in the vacated ammo bunker. Result: A schnorkel endurance of 6000 nautical miles at 10-12 knots, and a top submerged speed of 9 knots for 30 nautical miles. Depth charges effectiveness is halved.

1944-model: Overhaul the u-boats with the variable pitch propeller, and upgrade the generator from 375 hp to 580 hp. Top submerged speed is 15 nautical miles (XXI had 17.2). Depth charges effecitiveness is much less than 1/4.

I must say I like esl´s solution better than the XXI.

Full post from els below:

http://www.alternatehistory.com/discuss ... p?t=134297

An alternative to the earlier Type XXI scenario.
The keys to the Type XXI programme where greater submerged endurance through tripling the battery capacity and increased underwater speed through greatly increased electrical generator power allied to a more streamlined hull/turret plus a Schnorkel.

The Type XXIII had an endurance of 175nm @ 4knots and top submerged speed of 12.5 knots. The Type XXI had submerged endurance of 285nm @ 6knots and top submerged speed of 17.2 knots. However the initial production model only reached 15.95 knots in initial test runs and the first models had to be cleaned up to reach ~17knots.

All this was achievable through the existing Type VII Uboat as a retrofit package. In fact the original designs for the “Type I” Uboat in the early 1930s [pu111], was a Uboat with 8.5-9knots top submerged speed and submerged endurance of 160nm @ 4knots. While the Type VII prototype was design to get ~8.5 knots top speed submerged.

By adding saddle tanks to increase surface endurance from 4800 –6000 nm, they sacrificed ½ knot off top speed. To reduce crash dive time from to 20 seconds, twice as much flooding slit area had to be adopted, resulting in another drop in the top speed of ½ knot. So the war production Type VIIC Uboats had top submerged speed of only 7.6 knots and an endurance of 80nm@ 4knots.

Reversing both of these should raise the top submerged speed back to ~8.5 knots. Further removing the flak and deck guns along with all the railings should increase the top speed again by 7%, to 9.2 knots.

[1] Finally a variable pitch propeller matched up to the existing generator should increase the top speed by 50% to 13.8 knots.

[2] By 1943 all new Type VII could be produced with the upgraded generator putting out 580 hp instead of 375hp of the original generator. Combined this should further increase the top speed to 15.9 knots.

[3] Replacing the existing ammo bunker and the bottom row of reserve torpedos with battery space would more than double the Uboat endurance.

All the above comes from Rossler’s “The U-Boat” , considered by many to be ‘the bible’ on German Uboat development and technology. Its also where the 100km detection range for the GHG sonar comes from at the start of the war. In one case in 1940, passive sonar detection occurred at a range of 100 nm or 180 km.

http://www.subsim.com/books/book_uboat.htm

According to Rossler, Steps 1, 2 and 3 were proposed to increase the effectiveness of the existing Uboat fleet in 1944; however overhauling the entire Uboat fleet would cause a significant delay in the Type XXI production schedule, so it was cancelled.

To change the history, all you have to do is have Walter working with Donitz in Uboat Development from the start of the war, as Donitz ideally wanted instead of being put in charge of Uboat ops. Walters emphasized that the key to Uboat success was high underwater speed and endurance from 1933 on. Given the mid war ASW crisis, Walter would then convince Donitz to push for earlier peroxide boat development, but in the meantime modify the Uboats as much as possible for higher underwater speed and endurance. So the initiative to beef up the Uboat flak through rebuilding the conning tower in 1942/43, would instead be replaced with an initiative to mount the Schnorkel Walter designed in 1933/34, inside a more streamlined tower with no armament. Along with welding over ½ of the flooding slit area, this should raise the top underwater speed to ~9 knots in 1942.

Removing the bottom torpedo row and placing extra batteries in the vacated ammo bunker, should then double the submerged endurance to 180 nm @ 4 knots. These changes should leave the existing fleet of Uboats with 10 torpedos and a submerged Schnorkel endurance of ~ 6000nm @ 10-12knots and a dash submerged speed of 30nm @ 9 knots. Combined with deep diving, this should reduce allied ASW effectiveness to ½ of historical levels. Thus “Depth Charge” attacks should only be 2% effective while “Hedgehog” attacks would only be 4% effective.

Read more on ASW effectiveness in the OG 51 reports…
http://www.ibiblio.org/hyperwar/USN/rep ... index.html

Instead of building the Type XXI Uboats in 1944, overhaul all the Uboats with the ‘variable pitch propeller’ mated to an ‘upgraded 580 hp generator’ to get to the >15 knot top submerged speed possible. Combined that should further drop allied ASW effectiveness to much less than ¼ of historical operational levels, so even the ‘Squid attacks’ late in the war would be only a few % operationally effective at sinking Uboats.

BTW reportedly 4000 Mark 24 torpedos were built, but the order had been cut back from 10,000 , so that could certainly change in response to greatly enhanced Uboat fleet. However the Mark 24 ASW torpedo would have been no use against the Type XXI Uboat or such a notionally overhauled Type VII/IX Uboat fleet, because @ 12 knots it was far to slow.

Mark 24 ASW torpedo.
http://www.navweaps.com/Weapons/WTUS_WWII.htm
This site reports that the Mark 24 acoustic torpedo was introduced in 1943 and was too slow to catch the Type XXI Uboat .

“Fido would have been too slow to attack the Type XXI U-boats and could be avoided by going very deep.”

http://uboat.net/allies/technical/fido.htm
Top speed of 12knots @ 15minutes.

[Lars]

Inspired by the electro-boats, in 1943 the Germans conducted a study about the possibility of greater underwater speed for the VIIC. Rössler, from whom esl draws most of his innovative thinking, notes that it was "perhaps surprising" that the Germans never retrofitted any of the VIIC or the IXs to meet the requirements of greater underwater propulsion. Rössler´s conclusion is that it was probably lack of any spare yard capacity that meant that the "electro" VII was stillborn as the XXIs and the XXIIIs took up the whole capacity.

Esl recommends Rössler´s book "The U-boat", an English version of the original German 2 volume "Geschichte des Deutschen U-bootbaus". For any technically interested u-boat freak, I really can´t recommend Rössler´s book(s) enough.

The central question one must ask esl´s electro VIIC scenario is just how much yard time the 1942-retrofitting and the 1944-retrofitting would take up. This is done from memony so feel free to correct me: In one end of the scale, we have the total building time for a new VIIC of 1 year (1942). At the other end smaller retrofittings took considerably less time. The fitting of the snorkel took 4-6 weeks if I recall correctly. Esl´s 1942-retrofitting of a new streamlined tower with a snorkel, removing the bottom torpedo rows and placing more batteries in them, removal of all guns, and the 1944-retroffing of the variable pitch propeller and a larger generator fall somewhere in between the two timespans. My gut feeling that the 1942-conversion might be the greater one so a guesstimate would be that the 1942-conversion would take up 2½ months of yard time and the 1944-conversion would take up 2 months of yard time.

In conclusion: 5 1942-retrofitted VIICs would take up the yard time of one new VIIC (12.5 months vs. 12 months). Six 1944-retrofitted VIICs would take up the yard time of one new VIIC (12 months vs. 12 months). In esl´s scenario, the yard trime that was used in our timeline with the adding of more flak guns, and the adding of the snorkel would be freed as the snorkel would be part of the 1942 conversion which would also mean that u-boats were unarmed from then on. The retrofitted VIICs are a hell of bargain for the U-bootwaffe and a faster bang for the buck instead of the XXI.

I´m not a member of the Alternate History Discussion Forum and sadly I can´t find the time for yet another discussion forums. So again, if any of you are a member of that forum, please let esl know of this discussion and invite him here.

[red devil]

If WW2 had progressed any longer, these electric boats may well have caused problems in the Atlantic. The war eneded at an opportune moment, for the Allies!!

[Lars]

It is even worse than that, Red Devil. If the Germans start upgrading their VIICs in 1942 as suggested above, then the Allies are in real trouble by 1943. The schnorkel retrofitted VIIC u-boats have larger underwater speed and are more immune to depth charges due to speed, greater streamlining, and much better underwater evasion. Even more significantly they are much more immune to be discovered and to be attacked by aircrafts. The drawbacks are only 10 torpedos per u-boat and slower transportation to and from the battle area when snorkeling instead of sailing surfaced.

It is only a matter of doing the maths. Say, each of the upgraded VIICs sinks dubbel the amount of shipping per day in the Atlantic and the attrition rate per u-boat drops to one third. This is enough to threaten Britain´s life line across the Atlantic like never before in the war.

[red devil]

This is assuming that Britain's scientists didn't come up with something that would detect these 'new' boats. It is entirely possible that threat = solution.