ASW damage from AC

[Bullwinkle58]

ORIGINAL: witpqs

ORIGINAL: Bullwinkle58

ORIGINAL: AW1Steve

Sorry , I totally disagree with most of the points you made. Blair is a ww2 Submariner who became a historian , in fact many ww2 submariners that I've interviewed refer to him as THE WW2 Submarine historian , largely to some very good connection with the post ww2 submarine brass. He did several official histories.

I didn't realize that the FIDO was in service at the same time you were , or that it had a S-3 NFO connection.

Maybe you can't track a submarine on batteries, but I know many people who can and have. Crews that I've served on have on many occasions.

Clowns? Nice. You treat your former shipmates as well as people on the forum.

I'd go into more detail , but don't want to 1) go into techniques that may or may not still be classified. 2) want to waste any time as it's only a matter of time before you called me liar again , no matter what I say 3) lose my temper and say something I'd regret and get banned from the forum.

So let me simply say that I totally disagree with you on most everything you've said here. Not surprise, I generally do. [:(]

I don't want to get between you two, but I don't discount everything he said. Thinking more about it.

I think he was saying that tracking a sub on batteries--from the air--in WII wasn't happening. No sonobuoys or helos.

But the 24kHz thing does make sense to me on a technology level. Where I have trouble is in the tactics. When a D/E dives three things happen instantly in the ER when the diving alarm goes off. One of (usually) two watchstanders pulls the outboard induction valve shut. He then pulls the inboard induction valve shut. If the diesels are still running they're puling on the people tank air. Very painful, very fast. The second guy therefore stops the diesels as fast as possible. How fast? From the diving alarm fifteen seconds would be pretty good. that gives maneuvering time to get the main motors up and going on the battery so the OOD has way to evade as soon as the hull is under. You don't turn in the initial dive if you can help it. Messes up the angle, and slows you waaaay down. Get under, then change course.

So say it's night. A FIDO equipped patrol plane finds a surfaced U-boat charging batteries. Maybe it's got radar, maybe it's using it sparingly for RDF reasons. Probably by that era the plane has radar too, but maybe it's off for the same detection reasons. The plane starts a run in. How far out does it drop the FIDO? The fish has to drop, activate, stabilize, and listen for diesel injectors that have, at best, about 15-20 seconds of noise, then they're gone. Does the FIDO get one good steer and then become a straight-runner? That might be enough if it's dropped close enough to the sub, but aspect and sub speed are going to drive the contact geometry. If too far out or not broad on the beam the sub can get out of the cone of contact pretty easily and then your expensive FIDO is just a mini-me straight-runner.

But if it does get a hit of injectors, and does a 30-degree steer to compensate for the bad drop aspect given by the plane's hurrying crew, it could increase hit percentage I'd say. Not to what an active homer could do, but better than a gravity bomb dropped in the dark.

BTW, are you accounting for the fact that FIDO was dropped so close to the sub? The closeness might have forgiven a lot of shortcomings in the sensors.

I'm saying it HAD to be dropped close if the only sensor input was diesel injectors. For surfaced subs here. If snorkeling the injectors would probably stay on as the sub had a bad chance of knowing it had been dropped on. Injectors then would be a steady data stream to the FIDO, which could do continuous corrections all the way to contact.

But a diving sub would need to be dropped on very closely. And getting that close without the sub starting the dive would be a nice trick if radar had to be secured else it would give the plane away. That might be some of the source of the 2-pane attack profile Blair speaks of. One plane with radar off angle from the "dark" plane carrying the FIDO.

[witpqs]

Understood. Thanks.

[AW1Steve]

ORIGINAL: Bullwinkle58

ORIGINAL: witpqs

ORIGINAL: Bullwinkle58



I don't want to get between you two, but I don't discount everything he said. Thinking more about it.

I think he was saying that tracking a sub on batteries--from the air--in WII wasn't happening. No sonobuoys or helos.

But the 24kHz thing does make sense to me on a technology level. Where I have trouble is in the tactics. When a D/E dives three things happen instantly in the ER when the diving alarm goes off. One of (usually) two watchstanders pulls the outboard induction valve shut. He then pulls the inboard induction valve shut. If the diesels are still running they're puling on the people tank air. Very painful, very fast. The second guy therefore stops the diesels as fast as possible. How fast? From the diving alarm fifteen seconds would be pretty good. that gives maneuvering time to get the main motors up and going on the battery so the OOD has way to evade as soon as the hull is under. You don't turn in the initial dive if you can help it. Messes up the angle, and slows you waaaay down. Get under, then change course.

So say it's night. A FIDO equipped patrol plane finds a surfaced U-boat charging batteries. Maybe it's got radar, maybe it's using it sparingly for RDF reasons. Probably by that era the plane has radar too, but maybe it's off for the same detection reasons. The plane starts a run in. How far out does it drop the FIDO? The fish has to drop, activate, stabilize, and listen for diesel injectors that have, at best, about 15-20 seconds of noise, then they're gone. Does the FIDO get one good steer and then become a straight-runner? That might be enough if it's dropped close enough to the sub, but aspect and sub speed are going to drive the contact geometry. If too far out or not broad on the beam the sub can get out of the cone of contact pretty easily and then your expensive FIDO is just a mini-me straight-runner.

But if it does get a hit of injectors, and does a 30-degree steer to compensate for the bad drop aspect given by the plane's hurrying crew, it could increase hit percentage I'd say. Not to what an active homer could do, but better than a gravity bomb dropped in the dark.

BTW, are you accounting for the fact that FIDO was dropped so close to the sub? The closeness might have forgiven a lot of shortcomings in the sensors.

I'm saying it HAD to be dropped close if the only sensor input was diesel injectors. For surfaced subs here. If snorkeling the injectors would probably stay on as the sub had a bad chance of knowing it had been dropped on. Injectors then would be a steady data stream to the FIDO, which could do continuous corrections all the way to contact.

But a diving sub would need to be dropped on very closely. And getting that close without the sub starting the dive would be a nice trick if radar had to be secured else it would give the plane away. That might be some of the source of the 2-pane attack profile Blair speaks of. One plane with radar off angle from the "dark" plane carrying the FIDO.

RADAR might do it. MAD certainly would give you a datum with attack criteria. And if the sub has just dived , a periscope swirl (as it dived) would certainly give you a "flaming datum" which would probably be good enough. Heck , it was good enough for depth charges.

[Bullwinkle58]

ORIGINAL: AW1Steve

ORIGINAL: Bullwinkle58

ORIGINAL: witpqs


BTW, are you accounting for the fact that FIDO was dropped so close to the sub? The closeness might have forgiven a lot of shortcomings in the sensors.

I'm saying it HAD to be dropped close if the only sensor input was diesel injectors. For surfaced subs here. If snorkeling the injectors would probably stay on as the sub had a bad chance of knowing it had been dropped on. Injectors then would be a steady data stream to the FIDO, which could do continuous corrections all the way to contact.

But a diving sub would need to be dropped on very closely. And getting that close without the sub starting the dive would be a nice trick if radar had to be secured else it would give the plane away. That might be some of the source of the 2-pane attack profile Blair speaks of. One plane with radar off angle from the "dark" plane carrying the FIDO.

RADAR might do it. MAD certainly would give you a datum with attack criteria. And if the sub has just dived , a periscope swirl (as it dived) would certainly give you a "flaming datum" which would probably be good enough. Heck , it was good enough for depth charges.

Yeah, but once you have a periscope swirl you haven't had injectors for about 30-40 seconds.

[AW1Steve]

ORIGINAL: Bullwinkle58

ORIGINAL: AW1Steve

ORIGINAL: Bullwinkle58




I'm saying it HAD to be dropped close if the only sensor input was diesel injectors. For surfaced subs here. If snorkeling the injectors would probably stay on as the sub had a bad chance of knowing it had been dropped on. Injectors then would be a steady data stream to the FIDO, which could do continuous corrections all the way to contact.

But a diving sub would need to be dropped on very closely. And getting that close without the sub starting the dive would be a nice trick if radar had to be secured else it would give the plane away. That might be some of the source of the 2-pane attack profile Blair speaks of. One plane with radar off angle from the "dark" plane carrying the FIDO.

RADAR might do it. MAD certainly would give you a datum with attack criteria. And if the sub has just dived , a periscope swirl (as it dived) would certainly give you a "flaming datum" which would probably be good enough. Heck , it was good enough for depth charges.

Yeah, but once you have a periscope swirl you haven't had injectors for about 30-40 seconds.

The torpedo 1st began a circular hunting pattern at 15 kts. I don't think too many ww2 subs ran that fast for long on batteries. If it didn't run into the sub, I'd imagine it would pick up some kind of noise. The FIDO is quoting as having a 33% success rate. A sub trying to clear datum would be going fast and turning tight. That should make a fair noise, considering the sub in question has no idea that he's being acoustically hunted. Combine that with MAD , and Sonobouys , both of which entered wide spread service about the same times as FIDO, and maybe 33% is not all that unreasonable.

[Bullwinkle58]

ORIGINAL: AW1Steve

The torpedo 1st began a circular hunting pattern at 15 kts. I don't think too many ww2 subs ran that fast for long on batteries. If it didn't run into the sub, I'd imagine it would pick up some kind of noise. The FIDO is quoting as having a 33% success rate. A sub trying to clear datum would be going fast and turning tight. That should make a fair noise, considering the sub in question has no idea that he's being acoustically hunted. Combine that with MAD , and Sonobouys , both of which entered wide spread service about the same times as FIDO, and maybe 33% is not all that unreasonable.

If that was the attack profile it didn't home on 24 kHz diesel injectors, for the reasons I've outlined. They're very temporary unless snorkeling.

In the USN it was normal to dive on surfaced course to at least 150 feet before setting an evasion course. Deeper was better. If there was a layer doctrine was to get below it before changing course. From your first days in subs you are taught "depth is life." (Like speed for airedales.) If you're in trouble you go deep, then try to get away. There's no benefit in letting the attacker watch you turn 70 degrees off the last course he had eyeballs on you.

Against DCs generally they didn't turn tight. The tighter the turn the more speed bleed, plus you make more rudder and plane noise. You go deep, below the layer if possible, rig for DC, rig for silent running, and slowly come to a first evasion course, using the skimmers' convoy pattern last seen if advantageous, plus any geographic or weather factors which help. A squall would be great.

Against a FIDO this would be a bad set of moves, IF the FIDO had sensors which could pick up something a sub does on batteries, every time. I don't know what that frequency would be, which is why injectors makes some sense. But they don't work for the battery evasion phase.

[vettim89]

ORIGINAL: witpqs

ORIGINAL: witpqs

I'm also questioning Sandman's dismissal of "92 lbs HE", which seems to ignore the existence of shaped charges.

Further on this, according to Wikipedia Hedgehog had 30 pounds of TNT or 35 pounds of Torpex. Did Hedgehog sink any subs?

http://en.wikipedia.org/wiki/Hedgehog_(weapon)

Ah yeah, USS England

Hedgehog and its little brother Mousetrap where different animals altogether. The were forward fired as the attacked crept up on the submerged sub firing a large pattern right over the top of it. The projectiles sank rapidly and had a shaped charge warhead. They were basically a bazooka shell that sank. The shaped charge created a super heated jet that punched a hole right through the pressure hull

[witpqs]

ORIGINAL: vettim89

ORIGINAL: witpqs

ORIGINAL: witpqs

I'm also questioning Sandman's dismissal of "92 lbs HE", which seems to ignore the existence of shaped charges.

Further on this, according to Wikipedia Hedgehog had 30 pounds of TNT or 35 pounds of Torpex. Did Hedgehog sink any subs?

http://en.wikipedia.org/wiki/Hedgehog_(weapon)

Ah yeah, USS England

Hedgehog and its little brother Mousetrap where different animals altogether. The were forward fired as the attacked crept up on the submerged sub firing a large pattern right over the top of it. The projectiles sank rapidly and had a shaped charge warhead. They were basically a bazooka shell that sank. The shaped charge created a super heated jet that punched a hole right through the pressure hull

I confess it was a loaded question! [;)]

[btbw]

Again - Fido designed for atack subs, not ships. It why Fido was targetting submerged subs. For exclude ability for attack surface ships which can be current target of subs (inside order of dozen of merchants ships) or which pursuited sub (KV, DE, DD etc).
Fido homing system have limitation on receiving noise signal from upper area if depth lesser then 40ft. First torpedoes had initial search pattern started on 50ft, but that removed with 150ft! What diesel can run on 150ft, sorry?
With care of own ships (Nazi dont have in Atlantic Surface Taskforces right?) deeper noise homing system solve problem of background noises coming from surface (wakes, wind, bio and own ships).
Diesel-runned subs dont need Fido for kill them. Just bomb or DC. Sub can be easy detected and attacked from plane. But if sub dive deeper - then you need series of attack by DC (or very fast bombing run). Fido solve this problem.

[Bullwinkle58]

Found this description of the targeting system on the Cutie, which was a modified FIDO made to launch from subs. The description doesn't say so, but everything in it seems to indicate it worked on broadband, not narrowband, data, most probably in the aural range.

" Target detection was accomplished by four hydrophones symmetrically arranged around the circumference of the torpedo mid-section in the left, right, up and down positions. Such an array is useful for target acquisition because the four hydrophones together cover essentially all directions from the torpedo and for homing because "body shadow", meaning that the hydrophone on the right side, for example, being in the acoustic shadow of the torpedo body could not hear a target on the left side, provides directionality. The basic idea is to compare the signals from the left and right hydrophones and move the rudder in such a way as to steer towards the stronger signal. In the BTL implementation of this scheme, the hydrophone signals were amplified, rectified and subtracted. This net signal was combined with the voltage from a potentiometer which was coupled to the rudder. The combined signal drove a DC amplifier which, in turn, controlled a differential relay that caused the rudder motor to move in the appropriate direction to reduce the input voltage (hydrophone derived voltage plus rudder potentiometer voltage) to zero. The vertical control circuit was identical except for including inputs from a hydrostat that measured depth and a pitch pendulum, which were also voltages derived from potentiometers. These signals caused the torpedo to operate at a fixed depth until a sufficiently strong acoustic signal was received. When such a signal was detected, the hydrostat/pendulum control was disabled and acoustic depth control prevailed. As a safety feature, acoustic depth control was disabled and hydrostat/pendulum control re-established if the torpedo dove below a limit set to about 150 feet. These control systems produced rudder angles that were proportional to the difference in strength between the signals from the right and left (or up and down) hydrophones.

It was recounted by J.J. Ott, that it was fun (during operational checks) to make noises from several directions and watch the 'cutie' rudder and elevator wiggle around, trying to acquire the source. As they were an acoustic device, all effort must be made to insure that the submarine is quiet immediately after the launch or (being closer to the sub than the target) the torpedo would acquire the submarine. Since the Bergall failed to remove engine power before firing the first 'Cutie', it was the "loudest" target found when the 'Cutie' was released. The first 'Cutie' used fired by the Bergall against an enemy vessel, almost acquired the Bergall!

The enemy ship had to be "drawn" into close proximity to the submarine in order for the 'Cutie' to acquire the target. On the Bergall this was accomplished by rising to periscope depth, raising the periscope and "wiggling" the scope around, giving the enemy a better chance of seeing the periscope head. At this point the patrol craft would begin a run on the submarine. The Bergall would then drop to about 150 feet depth and wait as the enemy before firing.

The Mk.27 torpedo was based on the Mk.24. The original Mk.27 Mod 0 was a minimally modified Mk.24 with wooden rails to fit 21" torpedo tubes, and various arming, warm-up and starting controls to suit a torpedo tube, swim-out launch mode. Eleven hundred Mk.27 Mod.0 torpedoes, known as CUTIE, were built by Western Electric and delivered between June 1944 and April 1945."

http://www.bergall.org/cutie.html

[sandman455]

Sorry about the long time in replying. Don't get much time. Scanning the forums from my phone is about it and that is hardly conducive to formulating replies. Last Sunday at 4am I was just about to succinctly respond to all of your responses and retorts using the information that I still had in my head from 25 years ago about things worked. And then by chance I went to Uboat.net and started to read some ASW after action reports about the Mk24 FIDO.

With each one read, I had no choice but to conclude that I didn't know what I was talking about. Nothing made any sense.

When active duty, I briefly read something about it and always consider it to be a novelty weapon. Little was available and who cared, there was little point. Long gone from the inventory and any one familiar with modern ASW could figure out how it would work and why it was useless. Consequently, what I was reading in detail accounts of its useage during 1943 and 1944 knocked me completely out of my chair. So much so that Monday morning I start shooting off emails to long lost friends or starting up conversations with those I see daily about the Mk24 Mine and its brother the Mk27 torpedo. How could this thing work? Why the incredibly conflicting data about how it worked and how it was used?

For clarification, here is the breakdown of the contradictions regarding the Mk24/M27 weapons:

The after action reports of the FIDO's found on Uboat.net have the weapon being dropped on a recently submerged boat. The boat was frequently attacked prior to the drop with more conventional DC's and bombs. The boat was also strafed for self preservation of the attacking aircraft. As soon as the sub was no longer visible, aircraft immediately went to the FIDO. My theory about how this thing was homing on the diesel was junk. The diesel on the boat needs air and it can't run while the boat is submerged. My understanding about diesel-electric boats is that the diesel is killed just prior or after to the hatches all secured. That means we have a the Mk24 homing on something else. All sources report that it was the prop or even more specifically the cavitation on the prop. Now that's great and completely retarded.

The prop that was spinning FASTER and making more source strength while the Uboat was running on the surface. The prop was creating more cavitation while it was on the surface. It makes no sense. But wait it's even better. They gave the FIDO to the submarine community, call it the Mk27 CUTIE and told them it is wonderful on surface ships because it will home in on the prop. Ok, the Mk24 can't work on surfaced uboats but change it's name, and all of the sudden the Mk27 works fine on surface boats?!

And no we are not done. the contradictions are still coming. . .


The Mk24 FIDO was R&D during late 1941 through 1942. The weapon was ready for limited fleet introduction in the middle of 1943 and we see that they gave it to the CVE's that were working the mid Atlantic in defense of the convoys. In fact all drops that I stumbled across were from the CVE aircraft. Hmmm . . . that's a pretty limited introduction. Wonder why? Not a biggie just another odd shaped piece to the Mk24 puzzle.

Come 1944-45 the Navy had order a bunch of these things. They opted to dramatically scall back their order because. . . the weapon worked so well. I guess with all the bad guys sunk, they were projecting a surplus. And because all the bad guys were gone from the world the weapon was retired in 1947 about 3 years before the introduction of the Mk32 torpedo which was using the far more viable method of homing called active acoustics. Let's review this; we have an effective weapon retired at the start of the cold war. The Soviets were given a couple of type XXI german subs to play with. All of their initial submarine efforts (just like everyone elses) after WWII were heavily influenced by these captured boats. The Mk24 FIDO should/would have been highly effective against type XXI subs because they had a prop, they liked to dive. So why retire the weapon??

I never expected to find such a mystery. And while everything I had believed fit the puzzle I was forced to conclude that the after action reports clearly had me in the wrong. Hmmm. . .

I started asking around, by Friday, anyone I knew with ASW experience (all ex-navy or active duty, AW2 - O6) was sick of hearing about the FIDO. And all I got back from them was Wikipedia stuff back and yes it doesn't make sense. Thanks guys. When I asked for their best guess on the contradictions, their responses could be lumped into 3 possibilities.

1. They didn't know what they were doing or how their own weapon was working. Very big, all but two supported this with a retired warrant officer acoustic operator (P3/S3 type) being the lead evangelist behind the theory. "You know how effe'd up we were sandman - just imagine what it was during a raging war."

2. The second explanation is mine and I had only one other supporter, a retired O-5 who had S-3 flight time as well as ASWOC command experience. The AAR reports were forged. The contradictions are too great. Evidence supporting this theory would be the very limited delivery aircraft, possibly all restricted to CV ops. Perfect situation to control the data. If you read the reports - they all sound much the same as if written or re-written by the same person(s). Why would they forge the reports - well we both agreed that my initial premise about this being a useless weapon if anyone figured out how it worked is a major factor. Indeed, this is universally accepted by all I asked. The weapon should not work if the diesel is off, if it homes on the diesel. If the weapon homes off the prop, then it will work surfaced or submerged. The Mk27 confirms this. Espionage was as real back in WW2 as it is today. The US and especially the British had their share of enemy or neutral agent infiltrating their networks. To safe guard how this weapon worked, they controlled the utilization and any after action reports. That way the weapon would not be compromised by a infiltrated chain of command. Oh yeah, I admit, I'm on Pluto with this one. It was so bad the O-5 says it is good source material for a book on the weapon. [8|]

3. Finally the winning answer was provided by a former P-3 aircrew. I respected this person's opinion since he definitely had a far better understanding of the physical sciences than anyone I know. He's personal library is full of books I would be scared to pick up less I get ideas in my head that I could not reconcile with my own existance. He's also not the kind to speculate, rooting all of his answers with rock solid facts or scientific analysis. Point blank, after being challenged repeatedly to give me some answer to why all the contridictions related to the Mk24/Mk27. . . you know what he said:






"Bigfoot"



"That or the thing was just too slow (12kts) to work against a post war boat or even a XXI. It does work against escorts because they always loved to drop to a crawl when prosecuting a sub to improve their active acoustics. The Mk27 bagged them as they started their ASW prosecution. Besides, prop cavitation makes a broadband noise, it hits everywhere, including at 24 kHz. Given that the sub might be on full ahead to max its dive rate and increase its datum expansion, you should at least have something even minor off the prop. Looks like it worked 20-25% of the time so yeah maybe. It's all you got to make it work. On a surface ship the prop cavitation would only help the normal noise off the diesel which apparently also hits at 24 kHz. Also noteworthy is that the Mk27 torpedo was kept in service for another decade after the M24 because little had changed in their methods. All that said - I'm still going to say with 90% certainty that it is related to the bigfoot conspiracy."

Sounds good to me and thanks for reading. [;)]

[Bullwinkle58]

I think you dug up some good info here. Thanks for the effort.

As a sub guy I might think about this stuff a little differently, but not much.

The 12kts is very important, but very aspect dependent. On a closing target it would be fine--see my USS Bergal post. If the attacker is coming down the line-of-sight 12 kts is enough to still hit on a react if the attacker goes broad beam at the last minute. It's also, as your correspondent said, enough if the ASW platform is loitering to re-establish dived datum and maybe see an initial evasion course by the sub. In a stern chase range at drop becomes pretty key. A U-boat might do 7-8 kts on battery for an hour or so at most. But the FIDO couldn't do 12 kts. very long, and if the U-boat turned and gained time that way the 12kts would be a miss.

Cavitation, as you know, is a VERY complex acoustic topic. Cavitation by a surfaced vessel is very different in the physics than cavitation off a prop under sea pressure. The frequency spectrum is just different, and as depth increases most of the sound goes out of aural ranges. But the prop of a diving sub leaving the surface is really no different than the cavitation of a surface ship. Yes, a sub pounced upon by airborne ASW is going to at least a full bell as the angle comes on and MBTs fill. It's class-dependent, but sometimes a flank bell helps and sometimes it could work against developing max speed the fastest possible. Near the surface the prop blades, on their up-stroke, are often less efficient due to wave action and the sound emanating from it is largely a function of the interaction with the water-air interface. As the boat goes deeper that ends and the frequency spectrum stabilizes in a range and alters in absolute level. The one thing which argues for the weapon being designed to home on cavitation is that every sub has a prop and it's always spinning in a dive. Every time. Any other sound profile, from pumps to planes, might be a variable present or missing. The prop is the one fixed element to plan around.

On the issue of the CVEs getting the weapon I could imagine that was a political pull thing, or maybe a training and maintenance support issue. If you put it in one channel in one service it's a lot easier to manage the back end of the program, at least in start-up. Security is easier to manage too for sure; CVE pilots in mid-Atlantic were less likely to run their mouths than LBA ASW crews in the pubs in Britain, Iceland, or Bermuda.

Interesting topic though.

[witpqs]

I think you dug up some good info here. Thanks for the effort.

+1, Sandman.

On the aircraft deployment versus the name-change when deployed to subs: my first thought is that the air-dropped (convoy protection) version might have had a depth cut-out that prevented it going after surfaced vessels??

BTW, out of curiosity I'm still interested in that kill radius for a 15kt nuke. Also forgot to ask in that post, against what hull are those lethal-distance figures for? I'm sure not all submarine hulls are equally tough.

[Disco Duck]

Since Clay Blair was mentioned I looked up his Obit in the N.Y. Times.
http://www.nytimes.com/1998/12/20/us/cl ... rines.html

It does make me question his creditability. When he was editor of the Post the magazine lost a $450,000 libel suit. There are other questionable things in the Obit.

On the few times I have read about the Fido being used it was always against a Submarine that had just dived. It does sound like the design tried to take advantage of the broadband noise created during diving. During an airplane attack I can't see the Submarine going to silent running mode.

If, as other posters have mentioned, Submarines dive first and then turn, then maybe Fido had just enough course correction to increase the odds of a hit.

[sandman455]

ORIGINAL: witpqs
BTW, out of curiosity I'm still interested in that kill radius for a 15kt nuke. Also forgot to ask in that post, against what hull are those lethal-distance figures for? I'm sure not all submarine hulls are equally tough.

Hehe - not much and that's all I feel comfortable saying. To get some perspective - a Balao class sub was positioned 2000 yards away at PD when they set off a NDB in 1962. It was shaken but little else. The pressure hull of Balao had a test depth of 400'. For every 33' you go down you increase 1 bar or 14.7PSI. So if a titanium alloy Alpha could easily good handle 2000', maybe even 3000' you are talking about a minimum 48x increase in the capacity of a submarine to handle the stresses associated with underwater exploding ordnance.

As for the little chart - I don't remember. I think it was from a post-WW2 training aid/manual. I remember seeing it in an intro class to modern ASW back in 1986. So if it is post-WW2 stuff than I'd say it was probably for the typical 750t U-boat - a Type VII. For each sub you would have a different chart based on the quality of outer hull and inner pressure hull. I think it is far to say a Japanese or American sub would of had significantly bigger numbers. The significant thing to me when I saw the chart was not the rapidly decreasing effectiveness of more and more HE - but rather the EFFECTIVENESS of very little HE when it detonates directly next to the hull. Hence the reason for the hedgehog working so well when it got a hit. They didn't have shaped charges in them. They merely had contact fuses so if they hit the sub they detonated.

[msieving1]

From what I've read, the order to only use the Mk 24 against submerged U-boats was for security purposes, so that the target would not realize the attack was from a homing device. Similarly, proximity fuses were not issued to Army artillery units until late in the war to prevent the enemy from learning about the fuse from duds. The Mk 24 was clearly capable of homing in on surfaced vessels.

The first successful attack with the Mk 24 was by a British Liberator bomber, and the first successful USN attack was from a PBY. So no, they weren't issued only to CVEs.

The Mk 24 was retired in 1948 and replaced by the Mk 34, another passive homer that was in service from 1948 to 1958.

[Barb]

Interesting debate ... and I would like to add some oppinions:

1) Homing - I would go to find out what sound a propeller of a typical VII or IX class sub would sound on hydrophones. As they were not turning very rapidly (it is not a fan), its noise would be pretty low - in fact type VII-A had about 470 to 485 rpm on diesels and 322 rpm on electrics - that makes 8Hz frequency (8 revolutions per second) for diesel and 5Hz for electric. Even if counting each list of a propeller as contributing to the frequency that makes 15-24Hz frequency noise.

2) 24kHz piezo-eletric hydrophones does not mean, they are listening for 24kHz frequency... But that they are operating on 24.000 cycles per second. Otherwise 24kHz is pretty high frequency noise (human ear on average can hear sound coming at 20Hz to 20kHz) - I doubt anything mechanical on sub could produce 24.000 cycles per second.

3) Mk.24 (FIDO) minimal depth limit - allied ASW surface forces were often dispatched to the vicinity of spotted sub - so to use the torpedo near own forces would be risking a friendly fire - thus they were to remain under the safe depth. And to get the submarine to be successfully attacked by Mk.24 with depth restriction you will have to get the sub under the depth limit - thus the conventional DC attack to get the sub under the water.

4) Mk.27 (CUTIE) had no need for depth limit, as it was not usual to have submarine operating near its own surface forces and its guiding system was able to home on enemy ASW vessels

5) Mk.24 and Mk.27 speed limit was of little concern until revolutionary sub designs (like XXI and XXIII) went into service. Subs usually do not run on flank speed on their limited battery capacity, nor ASW vessels are sailing around fast, because their own noise would preclude the effective use of hydrophones ...

[Disco Duck]

While looking for information on FIDO i ran into this.
http://www.i-52.com

If you click on the tab for the avenger pilots you will see that they were listening to the subs propellers with a sonobouy.

So obviously the hydrophones could pick up sub running on electric.

[spence]

Comparing mid-40's ASW tech to 1980's-1990's or 21st century ASW is like comparing swords to machine guns.

Regardless of all the technical gobbolly-gook the statistics indicate that the Mk24 Fido hurt or killed submarines at about 3 times the rate that depth charges/bombs did. That is a statistically significant difference. Which is also irrelevant since the MK24 is not included in the Allied inventory.

The game system appears to allow only the Japanese to improve ASW technology and/or doctrine over their miserable performance in real life.

[AW1Steve]

ORIGINAL: spence

Comparing mid-40's ASW tech to 1980's-1990's or 21st century ASW is like comparing swords to machine guns.

Regardless of all the technical gobbolly-gook the statistics indicate that the Mk24 Fido hurt or killed submarines at about 3 times the rate that depth charges/bombs did. That is a statistically significant difference. Which is also irrelevant since the MK24 is not included in the Allied inventory.

The game system appears to allow only the Japanese to improve ASW technology and/or doctrine over their miserable performance in real life.

How much ASW experience do you have Spence? [&:]