WI:Krigesmarine type xxI

[McPherson]

In theory that would be the case but if all the submarine has to do is get beyond 10,000 meters (but let's say 25,000 meters so it has a good margin of error and can't be tracked on its immediately preceding course) from its target to be safe from hydrophones picking up the diesel noise then its batteries are easily capable of doing that.

Not according to the moving body problem. A quarter hour is not enough of a safety cushion.

Any close proximity object that isn't propagating is almost certainly no threat. The Allies tried to use visual searching from LRMP aircraft early on and U-boats evaded them without difficulty. If enemy search radar can be avoided by checking with the RWR there's no need to check for any non-radar-using vehicle with the submarine's own radar. Then the submarine won't give its position away.

Japanese aircraft had MAD. US boats had to assume a threat existed overhead and they had to check skies before they surfaced to recharge. Even their own forces bombed them by mistake (The Allies had MAD, too.) If the Germans don't then it is a win for the allies.

 

[McPherson]

More like 25% PK if a country has competitive torpedoes and sonar (and that wasn't even with the good US torpedo fire control computer).

Answered this above.

 

[Astrodragon]

There seems to be an assumption by some people that the Germans wave a magic wand and a flock of Type XXI's suddenly appear around the convoys.
Given the German predilection for using a new weapon early, and given obvious production issues, it isn't going to be like that.

What's far more likely is the Allies noticing a slowly increasing number of attacks with no U-boat being detected, plus intelligence reporting a new design of U-boat.
Since this new boat seems somewhat dangerous, they wont take their foot of the A/S pedal in 1943 as OTL, they will press it down harder. More LRMPA is pretty easy to ramp up - just tie up the bomber barons for a month or so. More escort carriers takes longer, but again can be speeded up considerably if seen as vital.
Submarine captains instinctively go deep on detecting an aircraft. Or Mars. Or even a seagull... so greater air/radar cover keeps them down and draining their batteries.

Attack by sonar isn't going to be at all practical until pattern runners/homing torpedoes are reliable. In the mid-30's, the RN decided that type of attack required a salvo of 10 standard torpedoes (hence the design of the T-boat). That's going to eat up the torpedo supply pretty quickly (granted, the RN studies seems to be against warships, a convoy attack will hit a few more ships, but it hardly seems an optimal mode of attack)

One other thing; the escorts do NOT sit in a ring around the convoy happily pinging away around themselves. They have a specific (and fairly complex) set of areas to sweep repeatedly, aimed to catch a U-boat trying to sneak into an attack position. A faster U-boat doesn't help as much against this, its still not fast enough to clear the sweeped sectors, and the faster it moves the more noise it makes (and the more obvious even its attack periscope is)

 

[McPherson]

There seems to be an assumption by some people that the Germans wave a magic wand and a flock of Type XXI's suddenly appear around the convoys.
Given the German predilection for using a new weapon early, and given obvious production issues, it isn't going to be like that.

What's far more likely is the Allies noticing a slowly increasing number of attacks with no U-boat being detected, plus intelligence reporting a new design of U-boat.
Since this new boat seems somewhat dangerous, they wont take their foot of the A/S pedal in 1943 as OTL, they will press it down harder. More LRMPA is pretty easy to ramp up - just tie up the bomber barons for a month or so. More escort carriers takes longer, but again can be speeded up considerably if seen as vital.
Submarine captains instinctively go deep on detecting an aircraft. Or Mars. Or even a seagull... so greater air/radar cover keeps them down and draining their batteries.

Attack by sonar isn't going to be at all practical until pattern runners/homing torpedoes are reliable. In the mid-30's, the RN decided that type of attack required a salvo of 10 standard torpedoes (hence the design of the T-boat). That's going to eat up the torpedo supply pretty quickly (granted, the RN studies seems to be against warships, a convoy attack will hit a few more ships, but it hardly seems an optimal mode of attack)

One other thing; the escorts do NOT sit in a ring around the convoy happily pinging away around themselves. They have a specific (and fairly complex) set of areas to sweep repeatedly, aimed to catch a U-boat trying to sneak into an attack position. A faster U-boat doesn't help as much against this, its still not fast enough to clear the sweeped sectors, and the faster it moves the more noise it makes (and the more obvious even its attack periscope is)

Wake feather, I would suggest, not just the periscope, but everything else is spot on as wargamed.

 

[McPherson]

One other thing (& this may be even more improbable): if the TSR/helo threat is so large, what are the odds of fitting *Type XXIs with SAR-homing SAMs? In that case, the radar mast isn't an a/c target--it's bait.

That is a tall order since the Germans never got a SAM to work properly during WW II. AFAIK, no-one did.

 

[phx1138]

Right back at you, so let me stick to what I understand and remind everyone, it is my opinion only and it is not gospel or personal EVER. Others can be right and I can be wrong, ya know?

To avoid thread derail, see my conversation. (Or send me one, if it didn't get sent....)

That is a tall order since the Germans never got a SAM to work properly during WW II. AFAIK, no-one did.

So I keep hearing, & I keep thinking, "Damn you people & your facts."

a. Maybe they are not as technically aware of snort boat limitations as we are today. That is one possibility.
b. Morale. They thought they had the U-boat problem licked and then here come the Germans with this new U-boat that they may not be able to solve quickly.

IMO, those are both true. They also apply TTL, IMO, even if they're an over-reaction or a mistake in the grand scheme.

a The USN and Canada though would NOT.

I'd like to think the Admiralty pros would prevail, & the Brits wouldn't, but... USN, I agree. RCN, TTL, might be shut out by default: RCN didn't have the ability to operate DDs, for lack of trained crews...& slow convoys, as said, might just have to stop entire for lack of escorts in that event. I don't see a way around that, TBH. Slow convoys with USN DEs, but much, much bigger ones? Say, 150 ships, instead of 80? (That does seem to make RCN effectively redundant...& the political implications of that aren't trivial.)

The Germans by 1944 are rank amateurs compared to what the Allies are doing

IMO, with an earlier *Type XXI, that would need to apply before mid-'43, or the panic may well produce chaos.

If it doesn't...IMO, it would put paid to any Italian ops (because *Type XXIs will sink too many, or cause too much to be held or delayed), & the net change in the war's outcome is near nil.

"Mr. Sikorsky can your helicopter dip a sonar and will it drop bombs?"

"Give me six months."

"Mr. Kaiser, we need more C-hulls modified."

"Give me three months."

That might do it alone. Can you get an *R-5 powered by an R1340 (or equivalent) in service, operating off launch flats, by Dec '42 or Jan '43? (It may need to be sooner...)

And I'll ask again: do you reject a heliborne PIAT-style *Hedgehog pod? Say, 10-15 warheads (only; no engines), radius about 200yd (50? Which might do it), pod weight around 600-800pd?

The Type 21 cannot attack in packs. It does not have the unimpeded communications of the early war U-boat.

Patrol line might be a better term. However, anything co-ordinated might be impossible at that.

I have to confess, I wargamed it for the storyline to see average results. If the subs try the tactics I postulated against a 1944 Allied convoy they will hardly hit anything by the torpedoes of the day. The periscope attack is about the only way to get efficient torpedo hits (about 25%) and by 1944 it is almost suicide.

I may need to re-evaluate my view of the German experience. It seems it's been a great deal harder for them than I've been giving them credit for.

 

[McPherson]

And I'll ask again: do you reject a heliborne PIAT-style *Hedgehog pod? Say, 10-15 warheads (only; no engines), radius about 200yd (50? Which might do it), pod weight around 600-800pd?

Might but I would like a bit more throw to keep the roiled water problem manageable. Of course Allied hydrophones may be good for about 10 km, but search-cone sonar is only good for about 2-3,000 m above the thermocline, depending on local acoustic weather.

 

[phx1138]

Might but I would like a bit more throw to keep the roiled water problem manageable. Of course Allied hydrophones may be good for about 10 km, but search-cone sonar is only good for about 2-3,000 m above the thermocline, depending on local acoustic weather.

My thinking is, if the helo is close on target, it wouldn't need a lot of "coverage", & with a contact pistol, I'm not seeing roiling being a problem. The idea is, a bunch of small bombs, rather than just one DC, given a payload limit around 600pd.

 

[marathag]

AFAIK, no-one did.

'Little Joe' came close, but command guidance wasn't ideal, as the Nazis found out

Lark was a beam rider, so better in that respect.

Last, you had Bumblebee, that was the basic for most of the Navy's 'T' missiles

 

[McPherson]

My thinking is, if the helo is close on target, it wouldn't need a lot of "coverage", & with a contact pistol, I'm not seeing roiling being a problem. The idea is, a bunch of small bombs, rather than just one DC, given a payload limit around 600pd.

The dipping sonar is going to be about 50 kg. Grenades will be about the size of Hedgehog bombs about 30 kg. Sink rates will be about 12 m/s. JFYI.

 

[McPherson]

'Little Joe' came close, but command guidance wasn't ideal, as the Nazis found out

Lark was a beam rider, so better in that respect.

Last, you had Bumblebee, that was the basic for most of the Navy's 'T' missiles

The tricks of the trade will take another decade and a half to work out. I think asking for a semi-active radar homer like SA-2 or the Big three; Terrier, Tartar and Talos is like asking for wire guided heavy weight torpedoes in 1944. The interrogator/control interfaces are not invented yet.

 

[marathag]

The tricks of the trade will take another decade and a half to work out. I think asking for a semi-active radar homer like SA-2 or the Big three; Terrier, Tartar and Talos is like asking for wire guided heavy weight torpedoes in 1944. The interrogator/control interfaces are not invented yet.

For Electronics, you did have active radar guided BAT, taht was good enough for ship or bridge sized targets, used it combat.

Pelican was the same thing, but was semi-active

Could also have BF Skinner teach his pigeons to tap at images of Japanese aircraft instead. They were to have used the same basic airframe that Bat and Pelican used

These had 1000 pound warheads. replace with smaller& proximity fuze and the JPL or Aerojet liquid fuel JATO as a sustainer,

RFNA and Aniline+Alcohol, so a bit hazardous, but these stats, could work

XLR7-AJ-1. Date: November 1942. Thrust: 26.67 kN (5,996 lbf). Unfuelled mass: 193 kg (425 lb). Burn time: 300 s. Height: 2.13 m (6.98 ft). Diameter: 0.91 m (2.98 ft).
Regeneratively cooled, 4 thrust chambers, pump-fed. A bit too cutting edge for the XP-79A.


Use with solid fuel rockets for a booster.

Parts eeemed to be there, but not assembled.

 

[McPherson]

The time differential is two orders of magnitude different. The machines have not been built with the feedback needed for up-date, and no animal is fast enough at those closure speeds of rocket and aircraft to make the correction. None. Not even men. Though mid-air ramming is tried. Merges with manned aircraft either require barrage attacks (bullets or rocket vollies) or pure luck. The signal chase on a sensor is the correct way and solved by 47. (APL) but it is the updating of positions in the two body problem (three body if a ship is the radar platform) that is the hang-up. That is what takes a decade.

 

[marathag]

The time differential is two orders of magnitude different. The machines have not been built with the feedback needed for up-date, and no animal is fast enough at those closure speeds of rocket and aircraft to make the correction. None. Not even men. Though mid-air ramming is tried. Merges with manned aircraft either require barrage attacks (bullets or rocket vollies) or pure luck. The signal chase on a sensor is the correct way and solved by 47. (APL) but it is the updating of positions in the two body problem (three body if a ship is the radar platform) that is the hang-up. That is what takes a decade.

Birds have been tested with 80ms reaction time, Humans is over 200 Photograpic records estimate that some birds withstand over 20G in maneuvers. But they need just to get close for proximity fuze, 20-30 feet away.

Ramming was accomplished by human pilots. Conditioned birds, it's easier. They think they will get food.

 

[McPherson]

Birds have been tested with 80ms reaction time, Humans is over 200 Photograpic records estimate that some birds withstand over 20G in maneuvers. But they need just to get close for proximity fuze, 20-30 feet away.

Ramming was accomplished by human pilots. Conditioned birds, it's easier. They think they will get food.

They tried in *44. with birds. It did not work with the two body moving problem at those speeds. Anything above 100 m/s merging with another object that fast is almost impossible unless it is about 40 milliseconds differential in vision refresh rate. Humans could barely ram at those speeds because our refresh rate is 8x FASTER than a pigeon's or just about any other animal. We evolved that way.

Even a hawk or an owl is not as fast in refresh rate. Maybe, just maybe a chimpanzee or a bat is. They can catch.

 

[AJE]

They had visual contact on that target (schnorkel), so probably used a visual range estimation - they are recorded as identifying what they saw as a periscope, so would know that they were pretty close.

The periscope attack is about the only way to get efficient torpedo hits (about 25%) and by 1944 it is almost suicide.

If they used unguided torpedoes, then that would make sense. But late-war acoustic torpedoes did not have the need for periscopes. It is very unrealistic to expect ASW weapons to kill a submarine 50% of the time based on things like FIDO's 22% OTL hit rate, and somehow expect a submarine acoustic torpedo with the same guidance and better knowledge of the acoustic environment than any sonobuoy or LRMP aircraft to get a <5% hit rate. These assumptions about the guaranteed ineffectiveness of WWII-era submarines against convoys and advanced WWII-era ASW are based on the complete incompetence of the Nazis at everything and the expectation that any hypothetical WWII-era submarine force would have been that incompetent. They are essentially a double standard and are not realistic.

Not according to the moving body problem. A quarter hour is not enough of a safety cushion.

It's only an issue if the convoy escorts or ASW forces know where the submarine is. Otherwise the safety cushion is in the time required to search an area, not the time it takes to cover that distance so the safety cushion is sufficient for the submarine to move further from the convoy on the surface or with snorkel.

Japanese aircraft had MAD. US boats had to assume a threat existed overhead and they had to check skies before they surfaced to recharge. Even their own forces bombed them by mistake (The Allies had MAD, too.) If the Germans don't then it is a win for the allies.

MAD can be defeated with appropriate degaussing/deperming. There is still no reason for the submarine to give its position away with radar when surfacing or snorkeling.

 

[Sam R.]

I’m a bit exhausted but “bird in a torpedo” keeps battering my mind.

 

[McPherson]

If they used unguided torpedoes, then that would make sense. But late-war acoustic torpedoes did not have the need for periscopes. It is very unrealistic to expect ASW weapons to kill a submarine 50% of the time based on things like FIDO's 22% OTL hit rate, and somehow expect a submarine acoustic torpedo with the same guidance and better knowledge of the acoustic environment than any sonobuoy or LRMP aircraft to get a <5% hit rate. These assumptions about the guaranteed ineffectiveness of WWII-era submarines against convoys and advanced WWII-era ASW are based on the complete incompetence of the Nazis at everything and the expectation that any hypothetical WWII-era submarine force would have been that incompetent. They are essentially a double standard and are not realistic.

a. FIDO drops were not singular. And when dropped were practically on top of the U-boat as her conning tower was awash, at least if doctrine was followed.
b. Acoustic torpedoes are farther away and can be decoyed or seduced by towed noisemakers.
c. Exactly! The Germans were deploying a weapon that got 1.6 freighters overall and then got promptly killed. They WERE incompetent. It was about 0.8 freighter for every dead U-boat at the end of it.

It's only an issue if the convoy escorts or ASW forces know where the submarine is. Otherwise the safety cushion is in the time required to search an area, not the time it takes to cover that distance so the safety cushion is sufficient for the submarine to move further from the convoy on the surface or with snorkel.

The torpedo is the exclamation point that announces "Here I am, come kill me! I'm a U-boat." Of course the escorts will know. That is what a launch transient does with a short ranged torpedo.

MAD can be defeated with appropriate degaussing/deperming. There is still no reason for the submarine to give its position away with radar when surfacing or snorkeling.

Actually if the MAD gear designers know their physics... it cannot be defeated by that means. It is how magnetic influenced torpedoes actually work, ya, know?

 

[Astrodragon]

If they used unguided torpedoes, then that would make sense. But late-war acoustic torpedoes did not have the need for periscopes. It is very unrealistic to expect ASW weapons to kill a submarine 50% of the time based on things like FIDO's 22% OTL hit rate, and somehow expect a submarine acoustic torpedo with the same guidance and better knowledge of the acoustic environment than any sonobuoy or LRMP aircraft to get a <5% hit rate. These assumptions about the guaranteed ineffectiveness of WWII-era submarines against convoys and advanced WWII-era ASW are based on the complete incompetence of the Nazis at everything and the expectation that any hypothetical WWII-era submarine force would have been that incompetent. They are essentially a double standard and are not realistic.


It's only an issue if the convoy escorts or ASW forces know where the submarine is. Otherwise the safety cushion is in the time required to search an area, not the time it takes to cover that distance so the safety cushion is sufficient for the submarine to move further from the convoy on the surface or with snorkel.


MAD can be defeated with appropriate degaussing/deperming. There is still no reason for the submarine to give its position away with radar when surfacing or snorkeling.

Acoustic torpedoes can be decoyed, and launching one increases the chance of the U-boat being detected. Not as much as a conventional torpedo, but its still dangerous for the boat. Especially as the WW2 weapons weren't an all-aspect weapon, to get a decent chance of a hit you really needed to be in a good position. Of course, the escorts know this as well.

If the U-boat is trying to escape an escort using its snorkel, its AWFULLY visible! And gets killed shortly afterwards.

Degaussing doesn't set the magnetic field to zero, it just reduces it so a magnetic mine has less chance of being set off. It was suspected (but not, iirc, actually proven) that it reduced the chance of a magnetic exploder on a torpedo going off. But it doesn't make you invisible.

 

[phx1138]

The dipping sonar is going to be about 50 kg. Grenades will be about the size of Hedgehog bombs about 30 kg. Sink rates will be about 12 m/s. JFYI.

Looking at the WP page, warhead is quoted as 35pd, & that's what I'm thinking: no motors, just a spigot-launch (PIAT-style). Also working in pairs (which I should've been clearer about...).