"Bastard" Electro U-boats From Early 1943?

[Lars]

This is my very first post on this forum, but I believe that I have the greatest chance of a good answer right here as the amount of collective knowledge here is staggering

We all know about the large XXI and smaller XXIII costal electro u-boats that came along during the last months of the war. The XXI was indeed an awesome machine and the Allies were in for a lot of trouble if it had been ready earlier.

The idea of the XXI and XXIII was born during an otherwise depressing meeting between the U-bootwaffe and professor Walther in November 1942. The meeting was about progress in the development of the Walter U-boats, which had a complicated but promising propulsion system. The message was depressing: As usual the Walter U-boats were postphoned and they were still far too expensive in fuel.

However, during the meeting two German engeneers Schuerer and Broecking had a bright idea: If the streamlined hull of the large Walter U-boat was filled with three times the normal battery capacity, the fast electroboat was a reality. The rest is history, as they say.

Now, what-if the Germans decided to spice up the existing U-boats and fill them up with batteries too to improve their underwater performance? It would be a stop gap solution until the real electroboats came off the line but I believe that it could have been implemented almost at once.

Think of this: The large 1,819 tonnes (submerged) XXI electroboat had the following specifications:

17.2 knots submerged top speed
340 miles range under water at 5 knots
4,400 horsepower submerged
372 battery-cells type 44 MAL 740, in total 33,900 Ah

The large 1,232 tonnes (submerged) IXC/40 conventional U-boat had the following specifications:

7.3 knots submerged top speed
63 miles range under water at 4 knots
1,000 horsepower submerged
124 battery-cells type 44 MAL 740, in total 11,300 Ah

Now, if the Germans had decided to increase the battery-capacity of the IXC/40 in late 1942 by, say 50%, it would solve many of the types problems in 1943 and 1944 (especially if a schnorkel was added). Adding 62 batteries to the existing 124 should have been possible by some minor rearangement of the interior decoration. The IXC/40 had 24 torpedos. Reducing that to 20 would free up a lot of space for more batteries. Other modifications which would find more space for batteries were probably also possible.

With 186 batteries, the IXC/40 specifications might look like this with a 50% increase in capabilities:

11 knots submerged top speed
95 miles range at 6 knots
1,500 horsepower submerged.

Increasing the top speed and range by 50% would more than dubble the area the Allied anti-submarine forces would have to scan. By early 1943, the Allied anti-submarine warfare would be much less effective and the U-boatwaffe much more dangerous.

What do you think?

More on batteries here

http://uboat.net/technical/batteries.htm

[Tim Smith]

Adding 62 batteries to the existing 124 should have been possible by some minor rearangement of the interior decoration. The IXC/40 had 24 torpedos. Reducing that to 20 would free up a lot of space for more batteries. Other modifications which would find more space for batteries were probably also possible.

Welcome to the forum Lars! And a great topic to start you off!

However, I'm not sure it would be that easy to fit extra batteries to a conventional U-boat. There was no spare space in a U-boat - absolutely none. The U-boat batteries were quite tall as well as wide, so I'm not sure if taking out the four torpedoes under the deck in the forward torpedo room would create enough space.

A better way to do it might be by converting the aft torpedo room into another engine room, putting two auxiliary electric motors in that space for more power, and extra batteries under the deck in that area.

You could maybe keep the two rear tubes, but they would have to be loaded in harbour, and it wouldn't be possible to reload them at sea. The two rear tubes might have anti-escort homing acoustic torpedoes loaded, for emergency use only.

Also because of the law of diminishing returns, which means you need more horsepower per knot of speed increase, I don't think that 50% more batteries would mean 50% more underwater speed. It would be less than that - and you'd need more powerful electric motors as well.

[Tony Williams]

Also because of the law of diminishing returns, which means you need more horsepower per knot of speed increase, I don't think that 50% more batteries would mean 50% more underwater speed. It would be less than that - and you'd need more powerful electric motors as well.

Quite so - extra battery capacity would only increase the underwater range and endurance, not the speed. You could help the latter by stripping off the external guns and other equipment and fitting some streamlining to the conning tower, but basically far more powerful motors would be required.

In my novel 'The Foresight War' I naturally allowed for Germany developing the Type XXI/XXIII much earlier. There was nothing very difficult about making them, after all, they didn't require new technology. In response, I had the British producing a fast S class sub as a practice target, stripped of armament and fitted with bigger motors from the larger subs and streamlining. For this purpose, endurance wouldn't be much of an issue. And of course the early introduction of fast escorts with ahead-throwing AS weapons.

Tony Williams: Military gun and ammunition website and discussion
forum

[Lars]

A better way to do it might be by converting the aft torpedo room into another engine room, putting two auxiliary electric motors in that space for more power, and extra batteries under the deck in that area.

You could maybe keep the two rear tubes, but they would have to be loaded in harbour, and it wouldn't be possible to reload them at sea. The two rear tubes might have anti-escort homing acoustic torpedoes loaded, for emergency use only

.

Tony and Tim,

Thanks. I knew there was information lurking out there

As you know I´m looking for a "poor man´s electroboat" which could be deployed as a stop gap solution imidiately after the electroboat idea was born in November 1942. The true electroboats took way too long to get ready. The first of the small coastal XXIII electroboats sailed out on January 21st 1945, and the first operational mission of the large XXI was on April 30th 1945.

A poor man´s electroboat needs:

A/ More engine power to get a higher speed both submerged and on the surface. Tim has suggested converting the aft torpedo room into another engine room and putting two auxiliary electric motors in that space for more power.

B/ More batteries to get longer underwater endurange and longer underwater range. Tim has suggested putting extra batteries under the deck in the aft topedo room after it has been converted into an auxiliary electric motor room. I´ve suggested removing four of the 24 torpedos to get more room for batteries.

C/ Better streamlining of the hull to get higher speed submerged. Tony has suggested removing the 88 mm deck gun. Tony´s more radical suggestion would be to streamline the conning tower. This would probably only be done to u-boats under construction as it can´t be done quickly.

So, two auxiliary electric motors plus more batteries in the aft torpedo room, more batteries instead of the four removed torpedoes, and the removal of the deck gun, all of which could be done in a few months, do we have a poor man´s electroboat by early 1943, gentlemen?

[Xavier]

extra battery capacity would only increase the underwater range and endurance, not the speed.

what use..? most u-boats that surfaced under long term attack did so because of bad conditions inside the boat (lack of oxygen-foul air..) no use going farther, faster, if the crew can't survive.

just my 2 cents.

regards

Xavier
Instandsetzungtrüppfuhrer

[Lars]

Xavier,

You are right that going faster, further doesn´t solve the air problem. However, going faster, further underwater would make sure that fewer U-boats would be chased until their air ran out. More would escape as the area the Wallied anti-submarine ships and planes would have to seach would magnify.

When the Allied did the calculations on the search area of the XXI they were horrified. It turned out that the seach area was nine (!) times greater than with the conventional U-boats.

Says V.E. Tarrant in "The Last Year of the Kriegsmarine". p. 207:

"The danger so narrowly averted is summarized by Correlli Barnett:

"The 1,600-ton Type XXI could cruise as far as the Pacific (from German ports) without refueling and reach a sprint speed when deeply submerged of 16 to 17 knots on her electric motors; as fast as most Allied convoy escort vessels ...

Moreover, during a pursuit at this speed the noise caused by water rushing and bubbling along the pursuer´s own hull would deafen his Sonars.

When dived to maximum depth under attack the Type XXI could cruise for nearly 300 miles at 6 knots on her electric motors, as against barely 100 miles and 2 knots by the VIIC U-boats ...

The anti-submarine forces´ existing operational arithmetic of search and kill would thus be rendered null and void: Whereas the area unit in searching for a traditional U-boat had been 31,400 square miles, it would be 282,000 square miles for the Type XXI."

In sum, the Allied navies had no ready technical or operational answers to the Type XXI."

It is clear from this quote that going father, further underwater is a great improvement even if the amount of air in the sub stays the same.

[Karwats]

Hi Guys

Soething else you might want to consider,apart from all the other ramifications about physical size etc.

Submarine cells are Heavy-very heavy around 800kg per cell. Adding 60 odd cells raises the weight by +- 50 tons, This may not sound a lot but it will have a huge impact on the bouancy and trim of the boat. Simply put it may not float with the added weight. This has implications for a number of systems onboard-most importanty the trim and ballast tank arrangements. With that much weight added you may not be able to trim the boat, which could mean that ac certain percentage of your fuel is unuseable, same for fresh water etc. You may require bigger air ballast bottles or higher pressure bottles. So adding weight to a boat has a host of assorted technical problems associated with it.

Now as for maximum underwater speed. This is normally something only achieved on trails and extremely rarely used,cetainly not to evade an ASW group-this is done at silent or ultra silent speeds 0.5-2 knots.

The question of air on the U boats came up a while ago, I'm convinced the U-boat crews with the personal CO2 scrubbing apparatus could easily maintain underwater operations for 3 days and more than likely a lot longer -5-6 days.

ASW tactics from WW2 are still practised today. The whole force will not bash about at maximum speed but pickets will be sent out at maximum speed 30 knots-on a "sprint" and subsequently drift and listen for any sonar contacts. Today this "sprint" is normally done by the Helo carried onboard ASW Frigates. But Frigates operating in pairs or groups will also employ this tactic especially if no helo is onboard.

In my view a streamlining of the hull could achive greater underwater speed with no extra battery capacity requirment. But more importantly a new tactical approach was needed earlier. This new approach only really came into effect with the Type XXI,when they employed submarine as opposed to submersible warfare. Submarines are designed to stay and fight underwater not only go underwater to avoid detection. if the Kriegsmarine had understood this earlier the various technical improvements that were available allready i.e. the schnorckel would have gone into series and standard production earlier.

[red devil]

My first post in here. I have done lots of research into Capt Johnnie Walker, his ships and his men. I am not sure that having the electro boats in early '43 would have made any difference. Walker, who certainly knew his stuff, could predict, to the minute when a U Boat would have to surface in order to expel CO2 and replenish oxygen. He was on the attack in the instance of the U202, when the U Boat went deep, a lot deeper than "normal" and Walker said that his depth charges could not reach the depth his asdic showed the U Boat to be, so instead he organised his "ring" and sat waiting, telling his men to have tea and sandwiches, as "the boat will not surface until 0002 hrs". Sure enough, on the dot, the U202 broke surface and was despatched back down again by the guns of Walker's sloops.

[Lars]

Hi Guys

Submarine cells are Heavy-very heavy around 800kg per cell. Adding 60 odd cells raises the weight by +- 50 tons, This may not sound a lot but it will have a huge impact on the bouancy and trim of the boat. Simply put it may not float with the added weight. This has implications for a number of systems onboard-most importanty the trim and ballast tank arrangements. With that much weight added you may not be able to trim the boat, which could mean that ac certain percentage of your fuel is unuseable, same for fresh water etc. You may require bigger air ballast bottles or higher pressure bottles. So adding weight to a boat has a host of assorted technical problems associated with it

Karwats,

I suggested removing 4 of the 24 torpedos. As each topedo weights 4.5 tonnes this would relieve the U-boat of 18 tonnes. This reduced weight alone would equal 22½ batteries, adding to the existing 124 batteries. The battery power would then go up 18%. Removal of the aft torpedo room would add two auxiliary electro motors with more batteries below the engines.

Removal of the the deck gun decreases weight even more and improves streamlining. There were probably other minor improvements which were possible, but which we can´t think of right now. The added batteries and the auxiliary engines would of course have to be placed so that the trim of the U-boat was affected as least as possible.

From the birth of the electro-boat idea in November 1942 to the first of the small XXIII were operational in January 1945, 26 months passed. The large XXI was only operational 29 months after the electro-boat idea was born!

I agree with you that the Kriegmarine needed a fundamentally new approach and that the XXI and the XXIII were the answers. However, I´m looking for improvement of existing u-boats in early 1943 that will give the U-boatwaffe greater survivability untill the Electroboats are ready.

[Karwats]

I'm trying to find a good line drawing (plan) of the type VII. See below a good picture of the Aft Torpedo room.



Pic from Ubootwaffe.net

This gives a good indication of the space problems involved and the affected systems.

In the centre are main vents for Ballast tanks-on the deckhead. These would probably have to be shifted to accomdate manual operation.

I'm pretty sure the machine on the left is an air compressor. Notice air bottles on the bottom left, so I'm guessing aft ballast bottles. There is also what looks like a fresh water tank on the bottom left.

Just to clarify, you want to fit extra E-motors for propulsion or extra generators for charging???? Both have some problems associated. If E-motors then somehow we need to transfer the power to the shafts which implies another gearbox somewhere. If generators,you need some way of venting the exhaust,either by fitting a new line or coupling to the existing-either way you also need a series of exhaust discharge valves for the generators.

Also looking at the pic I don't think there is any underdeck space available,it looks like the deck is actually the pressure hull or very close to it.

You could probably get away with removing some of the fish from the fwd torpedo room and fitting some batteries there,but I would like a good look at a drawing showing what other systems are also incorporated under deck. That being said you will still have very serious trim problems fwd with all the added weight,so somewhere a corresponding amunt of weight-or ballast would need to be incorporated, this in turn could negatively affext both speed and manueverability.

If someone has access to a good line drawing,please post it. I think this is a brilliant topic and i think we should make a serious go of it.

[Lars]

. Just to clarify, you want to fit extra E-motors for propulsion or extra generators for charging???? Both have some problems associated. If E-motors then somehow we need to transfer the power to the shafts which implies another gearbox somewhere. If generators,you need some way of venting the exhaust,either by fitting a new line or coupling to the existing-either way you also need a series of exhaust discharge valves for the generators.

Kawats,

I was hoping for both 2 auxiliary electro motors and more batteries.

I know this patchwork U-boat isn´t anyones idea of an ideal submarine but it might just keep the U-bootwaffe alive and kicking until the Electroboats are ready.

Anyone,
How much weight would the removal of the deck gun plus its shells save?

Off the cuff, I´d say that removing the gun increases the streamlining of the U-boat by 1-2%, giving it a little more speed and a little better underwater performance.

It all ads up.

[Xavier]

More electric motors are definitively a no-no

By 1943, cooper resources were already stretched to the limit.
we are not taking in consideration external factors that affect the design of "our" bastard.

regards

Xavier
Instandsetzungtrüppfuhrer

[Mark V]

In my view a streamlining of the hull could achive greater underwater speed with no extra battery capacity requirment.

I am with you. VII or IX "guppy" conversion is complicated by the fact that they didn't use electric drive, like US boats.

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

Mark V

[The Argus]

As far as I can tell from the VII drawings I've got, the deck in the photograph is either the aft trim tanks or aft torpedo compensating tanks.

On the otherhand I don't see why there's any need for more electric motors, it would be much easier just to replace the existing ones with larger units. They seem quite modestly sized in comparision to the batteries. But where you could put more cells... Ballast tank III is about the only sizable volume that you could tap into but then it is kind of useful for other things.

As for in the forward torpedo room, it looks like there's only a torpedo diameter or so under the floor plates before again it's trim and compensating tanks. Oh and the space for manual control of the bow planes right up under the breaches.

As far as I can see the only way to get more batteries into the existing designs is to take the route they did historically, add a 'belly tank' to the presure hull although in this case it might be best to use the tank for 'internal' ballast rather than batteries.

shane

[Lars]

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?