WI:Krigesmarine type xxI

[McPherson]

what does variable pitch propeller accomplish? have seen a projected 1 - 2 knots increase in speed (assuming in optimal case?) but for noise? or what is the solution?

The situation with a controllable pitch propeller (variable pitch screw or CTPP) is more to do with fuel economy and engine/motor load rating than it does with noise or speed. Imagine the pitch face settings on a CTPP as being akin to the gears on a automatic or in the case of the Type 21 a 6 speed manual transmission when so fitted. The CTPP also confers the advantage of not needing a reverse gear or a reverse motor as blades can be set to bite in reverse with the same rotator direction. It improves fuel use efficiency by allowing the engines/motors to operate at best designed constant load or fuel usage rates. Now at some speed ranges when the pitch set is too acute, popcorning noise or blade tip bubble-generated cavitation jumps up a half to full magnitude. The more spin velocity, with an oblique blade face angle set wrong, the better FIDO likes it. This is also true for constant pitch propellers CPPs. The problem is common to both but the Germans screw up by getting the blade geometry for the screw wrong on top of it. The Germans are not the only ones to do this. The French as recently as the Charles de Gaulle had to make a couple of tries to get the blade shapes right and the USS North Carolina is famous for the three times it took to fit her with the proper screws. It is an almost universal problem, because it takes tank testing and at sea powered runs and even that guarantees nothing. Of course once you get a screw shape and hull form flow geometry that works for an entire class of vessels, engineers are not going to screw around with it. (Pun!)

 

[Cryhavoc101]

It might for one year.

Here's why.

1. One of the things about the Battle of the Atlantic that is misunderstood is that the weapon launch platforms, the weapons used, and the target sets are geared fundamentally to several factors.
a. Signal detection threshold (misinterpreted as range in popular literature.)
b. Time to target run times or sink-rates with the various weapons the platforms launch platforms employ.
c. Velocity aggregates (Time over distance) otherwise known as tactical speed of all the objects employed in the three body problem of launch platform, weapon and target.
d. Angle solution deltas (again time over distance) popularly known either as no-escape zones or probability to hit or probability to kill in popular descriptions. While this involves an aspect function between launch platform and target and also depends on a weapon characteristic, a bomb dropping on a diving submarine versus a torpedo running to a target freighter, the point is that every weapon has a set of parameters where it will meet the target and a set where it will miss.
2. There is something called tactical speed. Targets, launch platforms and weapon systems have various tactical speeds, but when the aggregate system of systems is tallied up, the sensors employed, the various weapon classes used against freighters and submarines compared, one solves out a unique velocity aggregate mean. It is about 10-12 knots. Outer boundary escape where the tactical speeds exceed the existing launch platforms' ability to track is about 25 + knots. The weapon miss in most cases (freighter) is about 28 knots.

Hence the allied solution to the type 21 U-boat is ridiculously simple. Build fast freighters. Make the Germans speed up. Not going to happen with a snort boat and not going to happen with German torpedoes. The Allies are inside the technology OODA loop. As for what else?

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) and ASDIC/SONAR will have to graduate to magnetorestrictive GSF type German multichannel commutator actuated signal chase type sound gear. The Type 21 may be quieter than a Type VII on the battery, but she is twice as noisy on the snort. Read DEAD MEAT. The Germans did not raft their power-train properly. What they know about propellers is... well why do you think FIDO was designed to home in on screws instead of engine noise?

Hence a year. The US and UK will tighten belts, lose a million more tonnes of shipping and the Russians will be in Berlin on schedule as in the RTL.

IOW, the Type 21 changes nothing for the Germans. It might mean Russians on the Rhine though as the Allies might have to fort up and go defense in France for a few months. Who knows? Monty might not screw up Caen or Market Garden. The Allied truck shortage might not happen. Bradley might not screw up Falaise or the Bulge and things could still happen as in the RTL.

What I want the reader to understand, is that the western allies were not stupid. They knew (^^^) about this stuff and were perfectly willing to eat "wonder weapons" for the year it would take to reach Germany, even if it meant more casualties in men and treasure. The Russians were always there as the prime engine of allied victory, so the German doom was inevitable. The real question was where the allied meeting line was going to be.

Would the Allies need a better weapon than FIDO?

I mean yes the type 21 can sprint at 17 knots underwater - so can out run the FIDOs 12 knots and 10 minute endurance - but while type 21 has increased battery over earlier U Boats to allow it to cruise underwater without recharging for upto 2 days I suspect that battery life at 17 knots is measured in 10s of minutes

Now the Type 21 had 372 cells 44 MAL 740 (33900 Ah) vs the Type 7s 124 cells 33 MAL 800 (9160 Ah) - of course being built earlier the batteries on TTLs type 21s might not be as good!! But I have been unable to find out how long a type 21 can maintain its max speed. I did find its endurance at 5 and 10 knots - taken from post war USN studies of the Type XXI conducted at Portsmouth, NH, USA.

"The cruising range based on one battery discharge is 365 miles at 5 knots or 110 miles at 10 knots"

Which would suggest that at 17 knots it's going to rapidly run out of juice if it came under a sustained attack and had to keep running!

The other issue I can foresee in introducing a better weapon than FIDO in 43 is that I understand the limitations in the then Acoustic homing technology did not work well at higher speeds - but I suspect that a weapon capable of operating for longer that 10 minutes might serve!

 

[Draconis]

@McPherson They did build Victory ships that could cruise at 17 knots or so. How much faster would merchant ships have to travel to avoid attack by the Type 21s? How much horsepower would it take to push a Victory size freighter to the required speed?

 

[McPherson]

@McPherson They did build Victory ships that could cruise at 17 knots or so. How much faster would merchant ships have to travel to avoid attack by the Type 21s? How much horsepower would it take to push a Victory size freighter to the required speed?

Would the Allies need a better weapon than FIDO?

I mean yes the type 21 can sprint at 17 knots underwater - so can out run the FIDOs 12 knots and 10 minute endurance - but while type 21 has increased battery over earlier U Boats to allow it to cruise underwater without recharging for upto 2 days I suspect that battery life at 17 knots is measured in 10s of minutes

Now the Type 21 had 372 cells 44 MAL 740 (33900 Ah) vs the Type 7s 124 cells 33 MAL 800 (9160 Ah) - of course being built earlier the batteries on TTLs type 21s might not be as good!! But I have been unable to find out how long a type 21 can maintain its max speed. I did find its endurance at 5 and 10 knots - taken from post war USN studies of the Type XXI conducted at Portsmouth, NH, USA.

"The cruising range based on one battery discharge is 365 miles at 5 knots or 110 miles at 10 knots"

Which would suggest that at 17 knots it's going to rapidly run out of juice if it came under a sustained attack and had to keep running!

The other issue I can foresee in introducing a better weapon than FIDO in 43 is that I understand the limitations in the then Acoustic homing technology did not work well at higher speeds - but I suspect that a weapon capable of operating for longer that 10 minutes might serve!

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) and ASDIC/SONAR will have to graduate to magnetorestrictive GSF type German multichannel commutator actuated signal chase type sound gear.

What I wrote there is that the aircraft, surface escort team will need these kinds of improved weapons in a hammer and anvil attack. The destroyers will have to chase the submarine into the waiting LRMPs kill zone so she can drop two heavyweight fast torpedoes on the German. Depth charges (more likely hedgehog contact grenades) from the chasing destroyers are going to make the Type 21 a runner and it will be loud and deaf as a post as it runs. 770 yards / 700 meters (4 minutes) offset acquisition is good enough for the 1943 tech. The torpedo dropped behind will have to run hard in chase for about 500 seconds. The one dropped ahead will have to run to meet for about 100 seconds. (the hammer and the anvil). If one wants to go 1945, then drop active pinger sonobuoys to form a cross of Lorraine fence on the track and really drive the German sub nuts.

@McPherson They did build Victory ships that could cruise at 17 knots or so. How much faster would merchant ships have to travel to avoid attack by the Type 21s? How much horsepower would it take to push a Victory size freighter to the required speed?

Victory is too small.

About 210 meters long (689 feet) set beam at 18.28 meters (60 feet) and draft at 6.7 meters or 22 feet. Cruiser lines, transom stern, install 39,000 kW/shaft on 2 shafts. fuel bunkerage about 2,450 tonnes (2,700 short tons) #4 oil.... speed at flank, which is what a sub requires only when danger close, about 50 k/h (27 knots). otherwise cruise at 30 k/h (~ 16 knots) with a steam time of 400 hours. Enough to cross the Atlantic easily *(240 hours or shag 10 days). The sucker will displace about 12,000 tonnes standard and with cargo will be in burden about 21,000 tonnes. Figure a hundred of these round trip twice a month or 10 times a *44 year by June. That's D-day tonnage delivered. The Germans?

I would not want that war problem to solve if I was Herr Admiral Doenitz.

 

[WaterproofPotatoes]

Victory is too small.

About 210 meters long (689 feet) set beam at 18.28 meters (60 feet) and draft at 6.7 meters or 22 feet. Cruiser lines, transom stern, install 39,000 kW/shaft on 2 shafts. fuel bunkerage about 2,450 tonnes (2,700 short tons) #4 oil.... speed at flank, which is what a sub requires only when danger close, about 50 k/h (27 knots). otherwise cruise at 30 k/h (~ 16 knots) with a steam time of 400 hours. Enough to cross the Atlantic easily *(240 hours or shag 10 days). The sucker will displace about 12,000 tonnes standard and with cargo will be in burden about 21,000 tonnes. Figure a hundred of these round trip twice a month or 10 times a *44 year by June. That's D-day tonnage delivered. The Germans?

I would not want that war problem to solve if I was Herr Admiral Doenitz.

From what I remember, a Victory ship was good for 15.5kn with a diesel, 16kn with a Lentz engine and 17-17.5kn with a turbine; perhaps a bit more in All Ahead Bendix, and unlike a surfaced U-Boat, didn't need glassy calm to be able to do that.

Power required for speed scales geometrically rather than in linear fashion, so a ship that size with such high speed would require much more specialized equipment and tighter build tolerances, and the only cargo ships built that large at that time were Great Lakes freighters, and no cargo ship was that fast- it requires a lot of fuel.


Given those requirements, it would probably be cheaper to build more Liberty ships and just eat the increased losses; you can already build 'em faster than the Germans can sink 'em. Plus, a Liberty ship burns coal and chugs along on a shipyard-built engine.

 

[McPherson]

The build has other applications besides being a freighter or transport. For example fast tanker or seaplane tender. I now have a use for the work I just did on it.

...Those Marvelous Tin Fish: The Great Torpedo Scandal Avoided.

I did not expect that I would go that route, but after the stuff I just wrote there?

 

[WaterproofPotatoes]

Such a ship would make a great seaplane tender, attack transport or fleet oiler for sure!

 

[Astrodragon]

Would the Allies need a better weapon than FIDO?

I mean yes the type 21 can sprint at 17 knots underwater - so can out run the FIDOs 12 knots and 10 minute endurance - but while type 21 has increased battery over earlier U Boats to allow it to cruise underwater without recharging for upto 2 days I suspect that battery life at 17 knots is measured in 10s of minutes

Now the Type 21 had 372 cells 44 MAL 740 (33900 Ah) vs the Type 7s 124 cells 33 MAL 800 (9160 Ah) - of course being built earlier the batteries on TTLs type 21s might not be as good!! But I have been unable to find out how long a type 21 can maintain its max speed. I did find its endurance at 5 and 10 knots - taken from post war USN studies of the Type XXI conducted at Portsmouth, NH, USA.

"The cruising range based on one battery discharge is 365 miles at 5 knots or 110 miles at 10 knots"

Which would suggest that at 17 knots it's going to rapidly run out of juice if it came under a sustained attack and had to keep running!

The other issue I can foresee in introducing a better weapon than FIDO in 43 is that I understand the limitations in the then Acoustic homing technology did not work well at higher speeds - but I suspect that a weapon capable of operating for longer that 10 minutes might serve!

Fido's main advantage was giving an aircraft a usable sub-killer.
For ships, a deadly a/s weapon was already in the wings in early 43, the double squid with its specialised sonar set. 40% plus chance of a killper attack.
The allies were actually slowing down the manufacturing of A/S assets by the second half of 43, as they had basically won the battle and wanted to build more landing craft and ships. In the event of a suddenly more dangerous sub, this would rapidly be reversed.

 

[starman]

This. Unless the bugs are worked out you're going to lose a lot of crews operationally...

I'd assume the bugs were pretty much dealt with by April-May 1945 when XXIs began leaving on operational missions.

 

[McPherson]

I'd assume the bugs were pretty much dealt with by April-May 1945 when XXIs began leaving on operational missions.

Like the PZKW V at Kursk with its optical fire control system and fragile transmission gearbox , the Type XXI's first operational deployment cycle revealed serious design flaws. I mentioned the screws, but the other design flaws involved the dive control system and the battery cell banks which were needlessly complex and / or not mansafe to operate. In addition there was a problem with hull sweating endemic to any submarine that was only solved with a good air plant, that is air conditioning which the Type XXI does not have. Then there is the usual German naval design lack of attention to human factors such as exposed live connectors, mechanical and electrical, which are not safety caged and work spaces and travel paths that hinder rather than aid human movement. For example, that battery compartment: if you were more than 170 cm long (5 foot; 7 inches long), skinny and very flexible; you could not pretzel yourself into the battery compartment and snake slither along the crawlway platform provided to inspect the cells for lead terminal corrosion or acid spill onto the pressure hull. You would either electrocute yourself, burn yourself or hydrogen cyanide yourself to death by bumping or scraping into something you ought not. Speaking of acid spill; the cell cases leaked, so you had to put a man in there to look for those leaks every three watches to chemically neutralize the acid drip or something very bad happens to the pressure hull.

Other navies had these same exact problems (US dive controls were better [Squalus disaster.], but still not well thought out.), but why design against yourself to handle them? US boats had take-up decking plates over the battery cells for example.

Bunch of landlubbers there, designed the Type XXIs.

 

[Astrodragon]

I'd assume the bugs were pretty much dealt with by April-May 1945 when XXIs began leaving on operational missions.

You mean apart from the teeny issue of them falling apart on the slipway?

 

[McPherson]

Fido's main advantage was giving an aircraft a usable sub-killer.

FIDO was useful as the anvil. It worked best when there were surface assets that drove a U-boat into it, or when the U-boat was caught mid-dive. As I wrote previously, the mean aggregate tactical speed was 12 knots. This was FIDO's chase speed. You wanted to drop FIDO ahead of Mister U-boat if you could manage it and close slightly port or starboard so it would circle chase as the U-boat passed it by. I put up a video about this in the thread I mentioned (^^^).

For ships, a deadly a/s weapon was already in the wings in early 43, the double squid with its specialised sonar set. 40% plus chance of a killper attack.

The allies were actually slowing down the manufacturing of A/S assets by the second half of 43, as they had basically won the battle and wanted to build more landing craft and ships. In the event of a suddenly more dangerous sub, this would rapidly be reversed.

More explanation: the squid was a three barreled mortar that was designed with an automatic setter that could be updated from the fire control station as to bearing and azimuth as well as auto-set the time delay on the mortar shells. This set detonation depth. The U-boats depth was determined by a new type of British developed ASDIC sonar that could determine by hard return the U-boat's depth to within +/- 10-15 meters. With this information, TWO three barrel squid mortars could be used to drop triangle patterns of three mortar bombs on either side of the U-boat track above or below at time on target estimates of the U-boats predicted future position. All of this data and fuse setting is an automated process from the sonar shack or the bridge on the British destroyer or frigate to the mortar unit, with the loading crew having read/repeaters and mechanically able means to manually set the bombs and aim to drop the charges if the automatics failed for some reason.

40% PH was a tad optimistic. More like 25% in practice. And it would take more than a couple of dry runs at the U-boat to usually "zero" her in before the actual attack. There was a huge what if and still some guess work involved for the U-boat could turn out of path while the bombs sank to depth.

.

 

[eltf177]

I'd assume the bugs were pretty much dealt with by April-May 1945 when XXIs began leaving on operational missions.

Quality control by this point was all but non-existent, I've heard stories of shoddy welding along with the other problems. Now in 1943 hopefully at least that woudn't happen but getting the Type XXI into service in 1943 would probably involve pushing up the timetable with the same problems...

 

[DougM]

You have a couple hundred (at best) XXI vs about 2000 liberty ships plus whatever other ships The Allies had.
Presumthe type XXIs are going to have noticeable teething problems. It had issues in the real timeline when it was introduced years later and speeding it up is not going to help this any.
That is assuming that you CAN build a type XXI in 42/43. As you don’t have the experience in combat any sooner the in OTL so somehow you have to realize what needs to be changed with a lot less (perhaps no) combat experience. And then figure out how to make the changes and invent/design all the new things. This does not happen in 5 minutes. To design the type XXI you need to first learn from something what needs to be changed. Then you need to think of a what to make the change and the how to build it then build it and test it then repeat ALL of this until you are satisfied, once you have a “final” design you have to figure out how to build them in a production manor and how to get everything needed to do so from raw materials to a work force to subcontractors to transportation. And then when you get them into the hands of the military they need to learn how to operate them and the best way to use them so they need to create proceadures and manuals and such and work out a doctrine to best use them.
And in this timeline they need to do ALL of that in something like 30 months from first WW2 submarine combat to type XXI entering combat. Presumably it takes at least 6 months to go from a finished design to the first production unit entering service as you need to built tooling and such to get it into production. If you assume 12 months of combat to learn you have a problem with existing equipment and what the problem is that leaves you about 1 year to design a radically new submarine. I think your going to end up with a LOT of design and manufacturing issues.

 

[Astrodragon]

FIDO was useful as the anvil. It worked best when there were surface assets that drove a U-boat into it, or when the U-boat was caught mid-dive. As I wrote previously, the mean aggregate tactical speed was 12 knots. This was FIDO's chase speed. You wanted to drop FIDO ahead of Mister U-boat if you could manage it and close slightly port or starboard so it would circle chase as the U-boat passed it by. I put up a video about this in the thread I mentioned (^^^).



More explanation: the squid was a three barreled mortar that was designed with an automatic setter that could be updated from the fire control station as to bearing and azimuth as well as auto-set the time delay on the mortar shells. This set detonation depth. The U-boats depth was determined by a new type of British developed ASDIC sonar that could determine by hard return the U-boat's depth to within +/- 10-15 meters. With this information, TWO three barrel squid mortars could be used to drop triangle patterns of three mortar bombs on either side of the U-boat track above or below at time on target estimates of the U-boats predicted future position. All of this data and fuse setting is an automated process from the sonar shack or the bridge on the British destroyer or frigate to the mortar unit, with the loading crew having read/repeaters and mechanically able means to manually set the bombs and aim to drop the charges if the automatics failed for some reason.

40% PH was a tad optimistic. More like 25% in practice. And it would take more than a couple of dry runs at the U-boat to usually "zero" her in before the actual attack. There was a huge what if and still some guess work involved for the U-boat could turn out of path while the bombs sank to depth.

.

40% was in good conditions, of course.
As with most systems,in operational use you should broadly halve it.
But still its a U-boat killer (given the size of its kill area, even a miss would quite likely damage a U-boat. And while it took a minute or two to relad and for the water disturbance to die down, this still left the u-boat in the detection/kill zone.

And there is always Walkers patent attack by a group, that was so deadly no U-boat ever survived it to report on it!

 

[McPherson]

You have a couple hundred (at best) XXI vs about 2000 liberty ships plus whatever other ships The Allies had.
Presume the type XXIs are going to have noticeable teething problems. It had issues in the real timeline when it was introduced years later and speeding it up is not going to help this any.

Those Marvelous Tin Fish. Start about page 20.

I started with the Italian Ferreti snort and plonked it into the American Mackerel class submarine with a few tweaks. My point of departure is 1938. The Americans spend five years in that ITTL learning everything they can about how to use the technology and by 1942 they still have nothing but trouble with pressure slams, damaged diesels and sick sub crews. And unlike the Germans with the Type XXI, they do know what they are doing by 1942.

That is assuming that you CAN build a type XXI in 42/43. As you don’t have the experience in combat any sooner in the OTL so somehow you have to realize what needs to be changed with a lot less (perhaps no) combat experience. And then figure out how to make the changes and invent/design all the new things. This does not happen in 5 minutes. To design the type XXI you need to first learn from something what needs to be changed. Then you need to think of a what to make the change and the how to build it then build it and test it then repeat ALL of this until you are satisfied, once you have a “final” design you have to figure out how to build them in a production manor and how to get everything needed to do so from raw materials to a work force to subcontractors to transportation. And then when you get them into the hands of the military they need to learn how to operate them and the best way to use them so they need to create proceadures and manuals and such and work out a doctrine to best use them.

I would argue based on RTL post-war soviet, British and American experience that snort boats still are quirky as late as 1960. It takes time to figure out air circuits, sneeze boxes and the proper free float valves to make a snort boat work. Look at the problems the British had with their Upholders.

And in this timeline they need to do ALL of that in something like 30 months from first WW2 submarine combat to type XXI entering combat. Presumably it takes at least 6 months to go from a finished design to the first production unit entering service as you need to built tooling and such to get it into production. If you assume 12 months of combat to learn you have a problem with existing equipment and what the problem is; that leaves you about 1 year to design a radically new submarine. I think your going to end up with a LOT of design and manufacturing issues.

If one is prepared to accept an own goal (design defect or someone goofs in the boat) 10% loss of boat/mission rate as the Germans and the British did, then a Type XXI is just barely possible. Up to 100 German U-boat losses were self inflicted mission/boat kills in Type VIIs and IXs. This is rather startling. British rates (7 boats mostly T-boats) were similar. US rates (4-5 boats all by own torpedoes self-inflicted) were similar.

Not too dissimilar from aircraft own goals by the way. Wartime logic.

 

[McPherson]

That explanation I gave about FIDO acoustic torpedoes?

More details. You have to get close.

 

[PSL]

what does variable pitch propeller accomplish? have seen a projected 1 - 2 knots increase in speed (assuming in optimal case?) but for noise? or what is the solution?

Rossler states that Type-VII with variable pitch propeller could manage 12 knots submerged on same battery/generator. Streamlining with Walther style sail and eliminating 1/2 of the flooding slits should boost the top submerged speed to > 14 knots....not that much worse than XXI sub and fleet wide boat already. He reported such a conversion would take about a year instead of Type XXI production.

All you have to do then is to start the process in 1942. Instead of investing in winter garden effort of 42/43- convert every U-Boat sail into a streamline model -with a retractable schnorkel. Dr Walther designed such a device in 1934 for the experimental V-80 'fish-boat'. That Schnorkel could tolerate/function @ up to 25 knots. Finally remove rear torpedo and replace with small 'creep motor' for days of cruising at a few knots submerged. With 1/2 flooding slits closed it should manage 10 knots submerged.

At 10 knots submerged it will cut the effectiveness of Ballistic ASW weapons in 1/2 ....at 14 knots its more like cut down to 1/3 effectiveness. The Vast majority of all ASW was depth charges and by late war they had doubled the effectiveness'....This effort would revert the balance back to the U-Boat. Fully 1/2 of all ASW kills in 1942/44 were from air delivered ASW. If schnorkel neutralises air attacks , that effectively cuts # kills in half. If you factor in ASW ballistic attacks vs fast submerged , the result is 1/4 of the # kills.

A fast submerged Schnorkel sub was a game changer. But this will do nothing for the effective U-Boat attack success which plummeted from 1.6 MV per U-Boat month at sea to 1/10th MV per U-Boat month at sea. More subs surviving would equal more convoy attacks /about 4 times as many.

 

[McPherson]

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.

 

[bernardz]

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