How much shipping did the U-boats have to sink?

MickeyM

This is from u-boat.net:

'The Allies did a post war evaluation of U-boat courses and ASW patrol courses and found that the ASW planes missed snorkeling U-boats about 95% of the time. The find rate for surfaced U-boats must have been close to 100%. So we conclude that a U-boat with the big ball valve snorkel head was about 20 times harder to locate by radar than a surfaced U-boat. A well designed T-valve snorkel head is a lot smaller, rides lower in the water and is consequently more difficult to find. The issue is size and height above the water. The coatings used in WWII were not particularly effective.

I had an E-mail conversation with a retired US Navy ASW expert who tells me that snorkels were very hard to pick up with 1970s vintage analog radar. It was not until digital signal processing came along that the snorkel became relatively easy to spot.

The 3 cm radar came out about as fast as it was possible to do it. As mentioned above, it was no panacea against a well designed T-valve snorkel head. The truth is that the submarine (not the submersible) had the natural advantage vs. ASW until the advent of digital signal processing, both for radar and sonar. The caveat is that the U-boats had to become quieter with each generation and have appropriate weapons to shoot at escorts, i.e. wire guided acoustic torpedoes like Lerche. Given the current scenario, there is no reason why an improved XXI B could not be available in 1944 and an even better and quieter XXI C in 1945. The bottom line is that unless the Allies invent integrated circuits by 1945, the U-boat had the technical edge provided it used the appropriate tactics.

The top speed of the XXI was basically academic. The important issue was endurance at medium speeds. The correct way to march an XXI was to snorkel at 6 knots for about 4 hours at night to recharge the batteries and then go deep and run all day at 8 knots. Not a particularly fast way to travel, but relatively safe. The XXI was a complex weapon and required elite crews to be effective, so the safety of crew should have been of paramount importance. Fewer U-boats with elite crews can do a lot more damage than many U-boats with mediocre crews.

Actually, postulating what would have happened if the XXI had come out 2 years earlier is the wrong question. The XXI design was an unintended consequence of the Walter XVIII project and the hull was designed as a surface vessel. The XVIII was supposed to cruise on the surface until the time came to attack at which point it would submerge, go to Walter drive, make a high speed run at the convoy and escape. The concept only addressed the actual attack, but did nothing for the march to and from station, which was at least equally dangerous by 1943. The XXI was a workable solution to both problems, but it was far from ideal.

The real question to ask is what would have happened if the Kriegsmarine had recognized the theoretical danger of airborne radar back in the late 1930s. They would then have designed a real submarine, a single screw teardrop design. The theoretical advantages of such a design were known, and a bunch of such designs (types XXIX, XXX and XXXI) hit the drawing boards in 1944 when it was too late. Given a few years of development time, U-boats with at least twice the medium speed underwater endurance of the XXI could have been available, although their top speeds would not have been much higher. A U-boat which could run all day on battery at 10 - 12 knots was quite feasible with the available technology. If you throw in a thicker hull made from CM 351 steel, we can get a crush depth of 500 meters. In combination with wire guided torpedoes, a few hundred such boats would have closed the Atlantic.

Regards,
SuperKraut'

This leaves me with two questions:
1. Given time, could the KM develop an effective snorkel that can run at high speed?

2. What if the scenario in the last paragraph had come to fruition, and the KM had high-speed underwater boats, maybe with wire-guided torpedoes?
 

Deleted member 1487

MickeyM said:
In combination with wire guided torpedoes, a few hundred such boats would have closed the Atlantic.
Click to expand...
So basically ASB intervention? If the Germans had 300 Type VIIs in 1940 they could have done the same.
 

Cryhavoc101

The problem with the OPs question is that the British were the masters of ASW in WW2 - but even then until mid war placed their first line 2 and 4 engined bombers in bomber command and only 2nd line bombers in Coastal Command

Increased u-boat numbers and suddenly all that industry capable of spamming out 2 and 4 engined bombers is still spamming them out but many more of them as LRMPs (which is what should have happened anyway) and far more attention paid to U Boat production and their bases - earlier

And with that many U-boats the USA is going to 'notice' and be far less likely to enter the war with a serious shortage of Escorts as OTL
 

Carl Schwamberger

I think it is clear here quantity in not the answer. Aircraft were very sucessful in dealing with the submarines of OTL, & its easier for the Allies to send 200-300 additional aircraft to the Battle of the Atlantic that it is for Germany to add 20-30 submarines.

This leaves technology like the schnorkle, or adding in more of another weapons mix. Leaving aside technology for the moment, I am convinced a much different combination & tactics with existing weapons could have done the trick.
 

Astrodragon

wiking said:
You sure about that? From what I gathered there wasn't much effort invested in making it viable, it was all plowed into the Elektroboote
Click to expand...

Pretty much sure, yes.
The Royal Navy tried improving and using it post-war (without the wartime limitations on time and quality control), and after 5 years it was decided it was far too dangerous.
One of the test subs was nicknames HMS Exploder by her crew, who obviously weren't entirely thrilled.
HTP is, after all, a rocket fuel.
 

Deleted member 1487

Astrodragon said:
Pretty much sure, yes.
The Royal Navy tried improving and using it post-war (without the wartime limitations on time and quality control), and after 5 years it was decided it was far too dangerous.
One of the test subs was nicknames HMS Exploder by her crew, who obviously weren't entirely thrilled.
HTP is, after all, a rocket fuel.
Click to expand...
What changed that has allowed modern countries to use it safely? Also for the crew of HMS Exploder...they lived to nickname it, you sure it wasn't just their fear of the potential danger than actual danger?
 

Astrodragon

wiking said:
What changed that has allowed modern countries to use it safely? Also for the crew of HMS Exploder...they lived to nickname it, you sure it wasn't just their fear of the potential danger than actual danger?
Click to expand...

What's changed is far more knowledge about materials and handling HTP (a lot of this came out of the rocket/missile programs of the 60's and 70's). And it still isn't exactly safe.
But this knowledge simply wasn't there in 1940. Even 'normal' HP tends to happily disassemble itself if you look at it funny, having HTP around drafted ratings with no real idea of what they are dealing with...well, lets say I'd like to be at a safe distance. A few miles should do it. :)

Interesting article here :

http://www.rsc.org/education/teache...esources/34-7 Peroxide power in torpedoes.pdf
 

RamscoopRaider

Donor
wiking said:
Now Walter boats...
https://en.wikipedia.org/wiki/German_Type_XVII_submarine
Apparently the Swedes use this technology today and have world class subs. Those could survive in British coastal waters and ambush convoys before sprinting away.
Click to expand...
wiking said:
You sure about that? From what I gathered there wasn't much effort invested in making it viable, it was all plowed into the Elektroboote
Click to expand...
wiking said:
What changed that has allowed modern countries to use it safely? Also for the crew of HMS Exploder...they lived to nickname it, you sure it wasn't just their fear of the potential danger than actual danger?
Click to expand...
Modern subs most emphatically do not use Peroxide as an oxidant. The US, USSR, Germany and UK all tried, plus the UK and Russia tried using it in torpedoes. They all gave it up as a bad deal (Edit Russia might still use it in torpedoes)

Instead modern air independent subs, like the Swedish boats you mention, use stored liquid oxygen as a source of oxidant, or use fuel cells (not sure about French MESMA system, unclear if oxygen is stored as liquid or not). The Germans did experiment with a variant of the Type XXVIIB using this system AFAIK
 
Last edited:

Shevek23

As someone who thinks that the history of space travel might have been much improved by more use of hydrogen peroxide, I am the first to admit that while the stuff is pretty ubiquitous in industry (in much more dilute form, generally, than one would want for rocket or submarine power) it hardly is used in modern times for propulsion, and less used than it once was.

In rocketry, one can readily find anecdotes that have von Braun rejecting the stuff as dangerous in the wake of disastrous experiments by a compatriot. But in that case, the attempt was to mix HTHP with a fuel to make a fueled monopropellant...a very ill advised notion indeed!

What is less widely understood is that every V-2 they ever launched used a certain amount of HTHP anyway, as a pure, fuelless monopropellant to drive the turbo pumps of the alcohol and liquid oxygen primary propellants. And that the Soviet R-7 rocket, the one to launch first Sputnik, then Vostok, Voshkod and even Soyuz, also launched on engines pumped by stored hydrogen peroxide. I believe they eventually upgraded to alternate engines that eliminated this need but not I think until the 1970s, if even then.

From recent sources referring me to modern studies, it appears that one key to minimizing the hazards of stored HTHP is, strangely enough, to purify it as much as possible! It seems that although chem lab maxims and common sense would agree that mixing some water into anything should buffer its worst properties at least somewhat, that actually the presence of the dissimilar water molecule is as liable to trigger and perpetuate breakdown as it is to moderate the effects, and going from say 98 percent peroxide to 99.9 reduces the volatility of the stuff.

Another approach not tried in these classical days that would have helped is to chill the stuff down to a few degrees above its freezing point, which is colder than that of water.

As I understand it, Walter's experiments and prototypes were going to carry HTHP in plastic bags stored outside the pressure hull. Outside of tropical waters, this might have worked pretty well since deep sea water is quite cold, not much above freezing in fact. Concussion might be bad news, but if the stuff were nearly 100 percent pure and chilled I suppose it might put up with it.

But alas, in the 1940s no one knew that perfect purity would be helpful, nor that chilling would help, and anyway the technical processes of obtaining ultra-pure stuff was not perfected, nor could keeping the hull in cold water be guaranteed in operations, especially in tropical waters such as those between Brazil and West Africa, pr even the Caribbean. With concussions going on, warm water warming the peroxide bags, and purity at best in the 85-90 percent range, I think bags swelling and bursting would be all too likely.

Note that even if you can solve the problem of storing high-test peroxide, the upshot is you wind up having to haul about 8 times the mass you'd require if one could just obtain air for a diesel engine. And there is no way to restore the oxidant supply short of being topped off at a port or tanker ship of some kind, so range would be limited to when you've used up half the propellants. Nor can an engine that can run off peroxide/fuel mix be adapted to run off air and fuel; you'd either need two engines to burn fuel only when able to snort, or to rely exclusively on the stored bi-propellant, which would limit range badly.

An alternative might be to snort air when you can, and use some engine power to run compressors to attempt to extract and store liquid oxygen. I've never seen any figures on how much power it takes to obtain a kilogram of LOX. Also the machinery to compress it might run dangerously loud. If one could obtain and store LOX, trading off some diesel oil for the ability to run the main engines while submerged, for a while anyway, might be worthwhile, and it has the advantage that once the sub has a chance to surface, or just reach snorting depth, the oxygen tank can be refilled. Note that liquid air would be much bulkier per kg of fuel it could burn, but also much more suited to running a diesel cycle than pure oxygen would be, since the standard engine operation assumes 4/5 the molecules aspirated from air are nearly neutral nitrogen.

I've never heard of a diesel sub with auxiliary LOX tanks and a compressor to obtain more at sea. I would guess the ratio of fuel to be burned to LOX obtained might be unfavorable, that the equipment is heavy, bulky and unacceptably noisy in operation. But it might work?
 

Tonrich

MickeyM said:
Ok, so it looks like the British started the war with 19,500,000 tons of shipping, and the allies built 270,000-470,000 tons of shipping per month.
If the Germans sank 750,000 tons per month for 24 months, the British would be losing 280,000 to 480,000 tons of shipping per month, roughly 1.5 to 2.5% of their fleet size. In two years, the British would be down to 7,980,000 to 11,280,000 tons of shipping, roughly half their pre-war fleet.
This still seems like a lot of shipping. Could the British stay in the war with about 10,000,000 tons?
Click to expand...

You're not really looking at this issue with a proper understanding of Germany's goal. (Trust me I used to look at this issue the same way) Germany's goal was to reduce imports to Britain to the point that Britain would surrender. Sinking merchant shipping was one method of achieving the goal (although it tended to be a more permanent method then some of the others). I don't have my notes with me as I write this, but I'll speak in general terms. Once Britain declared war on Germany and Hitler decides to actually fight them (he still had hope they wouldn't fight) he declared the maritime exclusion zone around Britain. This forces Britain to reinstitute the convoy system which is an instant win for Germany.

Merchant ships typically sailed to and from ports carrying freight which is how they made money. Sometime they didn't have freight (had to sail in ballast) which means they weren't utilized (hence not making money). Ships are expensive things so there wasn't a "lot" of excess capacity floating around the world. The ships all sailed at their best economical speed in order to make maximum profit going from port to port. Once they got put in a convoy they could only travel in the same path as the convoy and at the speed of the slowest ship in the convoy, so they typically traveled more miles and at a slower speed then normal. Plus they also had to wait for the convoy ships to assemble at some point so they had delays where they weren't even sailing. Then when they get to Britain you now have a line of ships to unload, because I assume the docks couldn't unload all 40 to 70 ships at the same time so there's another delay. If prior to the war a ship made 12 cargo deliveries in a year, after convoy they were lucky to make 9, probably more like 8.

I've seen estimates that the convoy system cost Britain 25 to 30% of import tonnage without a ship being sunk.

So sinking ships is important, but so is bollixing up harbors and docks with mines, air raids of docks, supporting dock strikes by workers and even false sub reports that forces a convoy 20 miles out of the way. Everything that is done that forces a ship to sit longer then it should have helps the goal. The goal being reducing tonnage into Britain.

People get fixated on sinking ships (and that is important) but the crisis in 1940, 41 and 42 was more due to the reduced capacity (and higher need in wartime) then in actual submarine activities.
 
Last edited:

Deleted member 1487

Tonrich said:
You're not really looking at this issue with a proper understanding of Germany's goal. (Trust me I used to look at this issue the same way) Germany's goal was to reduce imports to Britain to the point that Britain would surrender. Sinking merchant shipping was one method of achieving the goal (although it tended to be a more permanent method then some of the others). I don't have my notes with me as I write this, but I'll speak in general terms. Once Britain declared war on Germany and Hitler decides to actually fight them (he still had hope they wouldn't fight) he declared the maritime exclusion zone around Britain. This forces Britain to reinstitute the convoy system which is an instant win for Germany.

Merchant ships typically sailed to and from ports carrying freight which is how they made money. Sometime they didn't have freight (had to sail in ballast) which means they weren't utilized (hence not making money). Ships are expensive things so there wasn't a "lot" of excess capacity floating around the world. The ships all sailed at their best economical speed in order to make maximum profit going from port to port. Once they got put in a convoy they could only travel in the same path as the convoy and at the speed of the slowest ship in the convoy, so they typically traveled more miles and at a slower speed then normal. Plus they also had to wait for the convoy ships to assemble at some point so they had delays where they weren't even sailing. Then when they get to Britain you now have a line of ships to unload, because I assume the docks couldn't unload all 40 to 70 ships at the same time so there's another delay. If prior to the war a ship made 12 cargo deliveries in a year, after convoy they were lucky to make 9, probably more like 8.

I've seen estimates that the convoy system cost Britain 25 to 30% of import tonnage without a ship being sunk.

So sinking ships is important, but so is bollixing up harbors and docks with mines, air raids of docks, supporting dock strikes by workers and even false sub reports that forces a convoy 20 miles out of the way. Everything that is done that forces a ship to sit longer then it should have helps the goal. The goal being reducing tonnage into Britain.

People get fixated on sinking ships (and that is important) but the crisis in 1940, 41 and 42 was more due to the reduced capacity (and higher need in wartime) then in actual submarine activities.
Click to expand...
https://en.wikipedia.org/wiki/Tonnage_war
 

sloreck

The problem with snorkels is that when waves wash over the exposed bit, the valve closes and the engines suck air from inside the sub unless shut down right away. This scenario is, shall we say, highly unpleasant for the crew. Having the diesels being shut off and then restarted over & over like this is not good for the engines. In totally calm seas, if you stick the snorkel up a good bit you can run at relatively high speeds without causing this problem. The North Atlantic is not known for those sorts of seas in any season. The higher the sea state the slower the sub has to go to avoid the combination of waves and wake washing over the snorkel. With the seas beyond a certain state (and this depends on the sub) you can't use the snorkel at all at any speed.

Prior to AIP propulsion, subs equipped with snorkels would usually transit on the surface in open ocean, only avoiding surfacing when they got close to their AO - this was typical for Soviet boats during the Cold War. Passive sonar was not good enough in WWII to pick up a diesel boat snorkeling as was the case by the Cold War, however the more you stick out of the water (more length of snorkel, radio mast, etc) the more likely you are to get a radar hit.

While not a bubblehead myself, I heard many stories about how crappy the snort submerging was, even to the extent of an occasional ruptured eardrum from the pressure changes in the boat.
 

RodentRevolution

Banned
MickeyM said:
T
The real question to ask is what would have happened if the Kriegsmarine had recognized the theoretical danger of airborne radar back in the late 1930s [1][2]. They would then have designed a real submarine, a single screw teardrop design [3]. The theoretical advantages of such a design were known, and a bunch of such designs (types XXIX, XXX and XXXI) hit the drawing boards in 1944 when it was too late. Given a few years of development time, U-boats with at least twice the medium speed underwater endurance of the XXI could have been available, although their top speeds would not have been much higher. A U-boat which could run all day on battery at 10 - 12 knots was quite feasible with the available technology. If you throw in a thicker hull made from CM 351 steel [4], we can get a crush depth of 500 meters. In combination with wire guided torpedoes [5], a few hundred such boats[6] would have closed the Atlantic.



2. What if the scenario in the last paragraph had come to fruition, and the KM had high-speed underwater boats, maybe with wire-guided torpedoes?
Click to expand...

Have you read the paragraph?

POD [1] is the foreseeing of radar, POD [2] is the foreseeing of radar's use against submarines on the surface rather than just aircraft. POD [3] is the commitment to designing an underwater boat, recall for this to be even remotely effective they need POD [1] to be early enough for POD [2] to be early enough to mean POD [3] is early enough to make a difference. [4] is probably not necessary which is good as it would likely strain German capacity enough to invalidate POD [6]. However the estimate of effectiveness does seem to rely on pod [5] your wire-guided torpedoes which are going to need a lead time all of their own and in practice amassing an operational force in the hundreds proved hard enough with proven designs whose manufacturing kinks were understood.

I mean anything is solvable with enough points of departure but at least [1] and [2]and possibly [4] and [5] actually require prescience as well. Worse some efforts like trying for a new and complex hull not to mention as explained the issues with propulsion by hydrogen bang-oxide might actually kill the project by themselves.
 

Astrodragon

The problem with a snorkel is that it doesnt make you invisible, just more difficult to spot.
I'd argue the 5% as being too low, the RN in the early 70's certainly thought it higher than that.
But you still have aircraft above you. The British can easily put far more LRMP aircraft out if they see the need - they just tell Bomber Command to go piss up a rope for a while.
Now the snag with just having a snort up is that unless you also have a persicope up (oops, there goes the 5%...), the first time you know about the aircraft is when the depth charges go into the water. Not good.But it gets worse. Lets assume your U-boat captain is sensible, and looking out for aircraft.But he wont know if they have, in fact, spotted him. Submariners hate aircraft, they go deep and wait for the nasty flying thing to go away. Each time you do this, you eat up more of your limited patrol time, reducing the effectiveness of the U-boat force, and quite possible fail to make contact with the convoy you're being aimed at.

Now a snort is certainly better than no snort, but its not a miracle.
 

Gannt the chartist

Not sure there is a tactical solution be interested to hear it though.


The base in 1935 is planning for enough crews for 14 large and 2 small subs to be available by mid 36, In 40 they had ramped up to 54 crews pa, in 41 250, 42 on 350 crews.


And until the capture of Norwegian and French bases the force has a long cruise to reach an operational area much of it beyond friendly air cover and well in range of land based air from early war ASW forces so you also have to increase the development and production of long range boats.


Increasing the size of the force means a very large infrastructure improvement to provide facilities and will provoke a British reaction, followed by a French reaction and a changed world as well as trade offs from other military developments.


When you get to sinkings the picture is not straightforward. Up to 42 most attacks are on ships not in convoy, hardly surprising as the escorts shoot back and which tend to be older, slower ships. The new construction is faster and speed of advance is a defensive measure. Unless the U boat is on the surface when you cruise at 10kts you have a 20-30% speed advantage over a submerged U boat. Having a snorkel does not change that over 6 kts the snorkel mast can break and the sound detection gear is useless.


Unless the boat can detect a target in the first place its just a lump of floating metal


As time passes from the fall of France the number of Ocean going Escorts increases, the number of easy targets decreases and the chance of getting into a fight with escorts goes up. You can make an argument that with 40’s technology on both sides the U boat force loses 3-6 months from the point where the U boat is forced to attack convoys or nothing at all. The German reaction to increasing escort numbers is to disperse to non escorted areas not charge in and die.


The Mid Atlantic gap is misleading. Mid Atlantic is the hardest place to detect a convoy or get into an intercept position, the closer you get to a port the more predictable the route. Why it becomes important and contentious in 43 is by then it’s the ONLY place a U boat could attack and hope to survive because the littoral is full of aircraft. Plugging the gap is a progressive thing with priority going to the most vulnerable areas, which are closer to ports.

A lot of the Air Forces objection is a reaction to the loopy orders of 42 which tasked the bomber force with attacking heavily defended and invulnerable U boat bases rather than strategic targets which orders are themselves a reaction to the second happy time which is itself attacks on unescorted, slow shipping. King has a lot to answer for.
 
You must log in or register to reply here.
Top
Top