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Subject: ROKN Patrol Corvette sucken by DPRK torpedo boat
YelliChink    3/26/2010 12:10:07 PM
Just happened 2150 Korean local time. Chinese reports say that it was DPRK torpedo boat. The ROKN corvette sunk is probably a 1200t PCC. I can't read Korean so I am not sure which one exactly. At this moment, 59 out of 104 crew have been saved so far. Best wishes to the still missing ones and condolence to families of lost sailors.
 
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jhpigott       4/5/2010 2:22:37 PM




Observation from Navy divers appears to support theories that the corvette Cheonan may have been dealt a heavy blow to its underside by a torpedo before it sank.




Divers said structures at the rear of the Cheonan were bent as if they had received a strong blow from beneath. The comments also give weight to theories that a "bubble jet effect" had caused the Cheonan to sink, referring to an intense shock wave and high-pressure bubbles that may have caused the vessel to split in half.




But visibility on the sea floor was extremely poor, allowing divers to see barely 30 cm. They ventured forward while closely observing the severed section so it is difficult to say exactly where, but the aluminum structure above the chief petty officer's mess was bent upwards as if due to shock from beneath.




The body of Senior Chief Petty Officer Nam Ki-hoon was found lodged inside the aluminum structure on the ceiling of the mess hall. Only the upper structure was bent upward, divers said, adding that it was difficult to determine how far the metal had been bent. A military spokesman said, "Those signs point to the vessel suffering from a strong blow from below."




h**p://english.chosun.com/site/data/html_dir/2010/04/05/2010040500841.html




v^2





Okay we have a failure mechanism identified, I think. That rules out the fantasies that those who said collision, grounding or explosion of on-board ordnance they suggested as hypothesis-all which most of us who do know what we discuss, rejected immediately as soon as we had sufficient evidence of the hull snap and separation.

 

This does not rule out the bottom mine, yet. It does still present the same torpedo problems as to times and methods. Depth charge is less viable. Almost rules out accident too.

 

H.


 


 



It is looking like S.K. is slowly narrowing down the culprit to the Cheonan sinking . . . and signs look to be pointing to N. Korea. 
 
If N. Korea is ultimately blamed through official channels in Seoul, the next most obvious question - What does S. Korea do about it, if anything?  That's probably the subject of anohter thread and I'm sure Pres. Lee has military/political advisors working on the question as we speak.
 
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VelocityVector    H.   4/5/2010 2:23:40 PM

FWIW the content of my previous post was a direct quote from today's Chosun Ibo.

I suspect that an encapsulated torpedo would have to be tethered or the strong currents might sweep it out of position.  If found, the mooring or capsule would leave a return address or at least diminish the desirable "mystery" impact the attack could be predicted to register.  Moored or unmoored, a static torpedo could get picked up by active sonar then neutralized or anchored upon or caught up in a fishing net.  It might strike an undesireable ship or be detected during hydrographic survey work.  If you lay one torpedo mine you can just as easily lay a few of them yet with all the post-Cheonan ship activity in the area there haven't been any repeat attacks.  These are some considerations that lead me to believe a vessel-launched torpedo struck Cheonan.  Regardless, I admit to being overly-fascinated by this event for some reason or other.  I think this stems from the whackiness exhibited by the NorKs over time, the NorK-Iran alliance, as well as the notion of a submersible speedboat/very fast submarine equipped with torpedos, iglas and special forces like the one we have photographed off Iran.

v^2

 
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VelocityVector       4/5/2010 2:29:34 PM
What does S. Korea do about it, if anything?
 
The South with US help can attempt to enlist Chinese help but that's about it.  A tit for tat could escalate beyond control, especially now that Kim Light is preparing to install his successor, NorK politics and factions could get interesting fast.  The South will do nothing.
 
v^2
 
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Hamilcar       4/5/2010 3:39:08 PM

FWIW the content of my previous post was a direct quote from today's Chosun Ibo.


I suspect that an encapsulated torpedo would have to be tethered or the strong currents might sweep it out of position.  If found, the mooring or capsule would leave a return address or at least diminish the desirable "mystery" impact the attack could be predicted to register.  Moored or unmoored, a static torpedo could get picked up by active sonar then neutralized or anchored upon or caught up in a fishing net.  It might strike an undesireable ship or be detected during hydrographic survey work.  If you lay one torpedo mine you can just as easily lay a few of them yet with all the post-Cheonan ship activity in the area there haven't been any repeat attacks.  These are some considerations that lead me to believe a vessel-launched torpedo struck Cheonan.  Regardless, I admit to being overly-fascinated by this event for some reason or other.  I think this stems from the whackiness exhibited by the NorKs over time, the NorK-Iran alliance, as well as the notion of a submersible speedboat/very fast submarine equipped with torpedos, iglas and special forces like the one we have photographed off Iran.


v^2



That is mighty close in and mighty shallow to swim in to lay a moored releaseable mobile mine, V^2. I am not unaware that some lunatic might try it, but against a north current that strong? Between INCHON and Jangsam Cape flow some of the trickiest underwater currents on Earth, as well as the ocean rising and dropping about three meters in some spots to almost fifteen! just depending on the local tidal forces. Moored mines are contra-indicated. Bottom mines, HEAVY ones might make a lot more sense-especially in the shallows. [This is speculation and by no means is even worthy of being considered a hypothesis yet.] Self propelled and self laying bottom mines are theoretically possible. Its just a torpedo with an auto-pilot and a GPS float antenna hooked to an INS GCU, and a sinker/arming feature that a normal bottom mine has. Fairly sophisticated weapon.      
 
H.
 
 
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VelocityVector    H.   4/5/2010 4:58:34 PM

Granted, but I wouldn't rule out an attempt by trained diehards or "errant fishing vessel" to emplace a moor.  These guys know and operate in the local waters and they have committed suicide on past mission fails.  You have to be a hardy soul, or fanatic, to even submerge in one.  A clear thing is that with enough petrodollars practically any nation can acquire the plans for all or key parts of all the technologies under discussion.  And I doubt the Chinese have assisted since before the last Bush Administration.

A question I ask myself is *why* either or both of the NorKs and Iranians would continue, uniquely almost, to invest in lightweight torpedo-carrying semi-submersibles through generational iterations if at least one of them didn't have field experience that convinced him the things are useful local launchers.  Although they don't fit our doctrine, I could see US applying them to SEAL support with gps mortar fire or even anti-piracy surveillance and interdiction.

v^2

 
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Hamilcar       4/5/2010 6:04:36 PM
1. Kill freighters.
2. Terrorusm.
3. The technical problems with training fanatics to calm "professional" standards is why kamikazes are rather less efficient than robot guidance. (Threw in a little HFE to liven things up.) Look how many botched suicide car bomb attempts there are. And that delivery  problem is SIMPLE compared to what this one is. Fanatics don't make good guidance systems.
4. I am open to any criticism or observation that you have as to why some of my ideas may not hold. The point about the DPRK gas knowledge of local conditions from past operations is valid. So I have a question....We suspect it took at least 150 kg of metallic powder augmented medium speed explosive to generate a water hammer to snap something the Cheonan in two.
 
The minimum size weapon is something called the APSETT, a 40 centimeter in diameter torpedo that weighs about 720 kilograms, carries a 60 kilogram shaped-charge warhead, impact fused, with a mean run time battery life of about 1000 seconds. Its maximum effective chase interval offset is somewhere in the neighborhood of 300 to 500 seconds depending on its slow or fast speed setting. The question is can an 18000 kilogram speedboat semi-submersible carry such a weapon? Can it do so and launch it without detection?
 
Maybe. But those would have to be PROFESSIONALS who cooked that crazy idea up and trained professionals who carried it out.
 
H.
   
 
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VelocityVector    "Professional" is Subjective   4/5/2010 7:04:45 PM

The minimum size weapon is something called the APSETT, a 40 centimeter in diameter torpedo that weighs about 720 kilograms, carries a 60 kilogram shaped-charge warhead, impact fused, with a mean run time battery life of about 1000 seconds. Its maximum effective chase interval offset is somewhere in the neighborhood of 300 to 500 seconds depending on its slow or fast speed setting. The question is can an 18000 kilogram speedboat semi-submersible carry such a weapon? Can it do so and launch it without detection?

If vessel-launched, the torpedo didn't chase, it passively intercepted a source of propulsion signal noise and closed with an approaching ship whose own course worked in favor of the weapon's range limitations at shallow depth in waters unfavorable to hydrophone detection, ship or land.  A <1000lb torpedo with a 100lb metal enhanced warhead could produce sheer effects on a 30-ft beamed target.  Beam is the key here.  Actual contact or proximate contact.  That's about the beam of a submarine target MK 46 and like are expected to destroy.  A bubble trail would go unnoticed unless a lookout screened for this and reports indicate no battle stations at the time.  So I doubt it was electrically-driven, I suspect this was a modern reactive plate drive design borrowed from paid-off Western sources along with its pumpjet which increased lowspeed efficiency and directed prop sound away from listeners.  As I stated earlier, I believe this event was scripted meticulously and it worked AFAIK.  That latter acronym the limit.  The NorKs took past beatings and now they dished back on their terms just before a political transition.  Or so I would have you believe ;>)

v^2

 
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Hamilcar       4/5/2010 10:34:27 PM
If vessel-launched, the torpedo didn't chase, it passively intercepted a source of propulsion signal noise and closed with an approaching ship whose own course worked in favor of the weapon's range limitations at shallow depth in waters unfavorable to hydrophone detection, ship or land.
 
Using the APSETT as the baseline technology...
 
That is a good point. Sound conditions though would have to be in deep water to set up a track solution and the launching boat would have to carry the optical or sound gear  because beyond two thousand meters the torpedo will not acquire on its own. The beach reflected sound of local underwater events would swamp its ability to discriminate.  This  stipulates a 3000-5000  meter launch position  from beyond the 50 meter depth line for Baengnyeong Island. Radar would just not be possible. It would be a estimated track bearing only shot as practiced in the days immemorial.
 
  A <1000lb torpedo with a 100lb metal enhanced warhead could produce sheer effects on a 30-ft beamed target.  Beam is the key here.  Actual contact or proximate contact.  That's about the beam of a submarine target MK 46 and like are expected to destroy. 
 
The APSETT is a sea-water battery-powered weapon designed to be released from an aircraft, chase nuclear powered submarines and kill them deep. It is one of the most advanced of an entire  family of Russian designed torpedoes that owes much to the American NT-37 fish which inspired this line of development. Data for the APSETT tends to be exaggerated but it is easily capable of Mk-46 performance which includes such terminal effects as you describe.
.  
A bubble trail would go unnoticed unless a lookout screened for this and reports indicate no battle stations at the time.  So I doubt it was electrically-driven, I suspect this was a modern reactive plate drive design borrowed from paid-off Western sources along with its pumpjet which increased lowspeed efficiency and directed prop sound away from listeners.  As I stated earlier, I believe this event was scripted meticulously and it worked AFAIK.  That latter acronym the limit.  The NorKs took past beatings and now they dished back on their terms just before a political transition.  Or so I would have you believe ;>)
v^2
 
Those are precisely the features one desires from a lightweight ambush torpedo, and the ones that certain intermediaries who would not want to be fingerprinted in a forensics aftermath would seek as an assassination weapon.
 
More food for thought...the front end of the weapon could be modified by removal of its active sonar-head feature  to carry more explosive as an ASuW weapon.
 
That notion, too, is speculation. We need motor fragments to even entertain the possibility.
 
H.
   
 
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VelocityVector    H.   4/5/2010 11:10:26 PM

What I failed to communicate apparently is my belief a single lightweight <1000lb torpedo was launched from some platform in a scripted scenario with distance and depth based on presets from observations past.  The torp using plate driven pumpjet run quietly on gyros until a predict point was reached at which stage the weapon opened its acoustics and possibly its throttle to passive listening and logic at speed.  It got head on bearings from starboard emanations between the leading edge of the target props and some triangular portion of the hull where the forward sound waves bounced off in the direction of the torpedo.  (They did not sound isolate Pohan back when it was developed; the shallow draft hull doesn't help this, it's a tin can.)  This area BTW is apparently where the 10 meter beam Cheosan hull fractured hurling a crewmember literally into the rafters as the primary wave amplified inside the resonant CPO mess.  I am with you supposing that fuel was traded, perhaps, for increased warhead yield.  It's all guesswork of course yet permissible fodder for discussion.  Shoal water impact or self-destruction do not hold water, on this aspect I believe we concur.  A weapon of some sort broke Cheonan.

v^2

 
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Hamilcar       4/5/2010 11:43:40 PM
Let's look at that. 

What I failed to communicate apparently is my belief a single lightweight <1000lb torpedo was launched from some platform in a scripted scenario with distance and depth based on presets from observations past. 

We still need to generate a track solution in local time to put a torpedo within local acquisition, especially if it uses acoustics and you plan an intercept vector. So that means pitting the fish within 80 seconds of the Cheonan's path +/-. Can we agree on this? 
 
If we can, then prior detection, observation and general track to determine when the Cheonan enters the intercept arc of the pre-determined engagement envelop is necessary. Further local observation of the local target track would be necessary to work out angle of course deflection (curve in the torpedo's trajectory) as per the target aspect Cheonan presents. Noth of those are local time variables that you cannot predict with certainty. If you goof the local solution then you can miss, and some RoK soldier will be photographed next to your torpedo he found on the beach.    

The torp using plate driven pumpjet run quietly on gyros until a predict point was reached at which stage the weapon opened its acoustics and possibly its throttle to passive listening and logic at speed.  It got head on bearings from starboard emanations between the leading edge of the target props and some triangular portion of the hull where the forward sound waves bounced off in the direction of the torpedo.  (They did not sound isolate Pohan back when it was developed; the shallow draft hull doesn't help this, it's a tin can.) 

Plausible. See where I pointed out that you have to solve in local time for target aspect since you cannot predict that aspect a full day in advance or even its speed or its appearance within your ambush parameters, none of this with certainty just by launch on bearing on the clock. You have to preset the target angle deflection into the gyro, even to just make the 80 second window in front of the Cheonan track, so that the Cheonan is within pickup or signal thresh-hold range of the torpedo's acoustics, as it circle searches. (Man, that cuts the offset time interval by almost 100 seconds!) 

This area BTW is apparently where the 10 meter beam Cheosan hull fractured hurling a crewmember literally into the rafters as the primary wave amplified inside the resonant CPO mess.  I am with you supposing that fuel was traded, perhaps, for increased warhead yield.  It's all guesswork of course yet permissible fodder for discussion.  Shoal water impact or self-destruction do not hold water, on this aspect I believe we concur.  A weapon of some sort broke Cheonan.

v^2
 
We concur. It looks like a duck and it quacks loudly..
 
H.
 
 

 
 
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