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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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Hamilcar    Somtijmes when the worm is caught he turns oriental.   4/2/2010 1:47:05 AM
Don't try the oriental game with me. I dealt with PRC Bandits.   
 
 
H
 
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jhpigott       4/2/2010 8:45:58 AM

 

Torpedo=again unlikely. The times of engagement and the ranges (interval) in the battle-space just don't add up.




 

     


 

 


 



Hamilcar - given that we have seen literally half a dozen different times given for the explosion ranging from about 9:15 to 9:45 I think at this point in time it may be a little premature to talk about times of engagement with 100% confidence.
 And if the SK govt was trying to down play any NORK invovlement, they've done a real poor job the last 24-48 hours. Consider the following -
 
1) President Lee Myung-bak asked Chief of Naval Operations Adm. Kim Sung-chan whether there would be identifiable traces left behind in a mine explosion, and Kim said it is hard to tell but there is also the possibility of a torpedo attack. Kim added it is fairly certain that the ship's ammunition storage did not blow up.
 
2) A senior military officer on Thursday said, "There is a 60 to 70 percent chance that the ship was hit" by a North Korean torpedo.
 
3) Cheonan Captain ?Reported Attack?

Immediately after an explosion that caused the 1,200-ton corvette Cheonan to sink in waters near the de-facto maritime border with North Korea on March 26, the Captain sent out a message to the Second Navy Fleet Command, saying, ?We are being attacked by the enemy.?

A military source on Thursday said Captain Choi Won-il sent the message using his mobile phone, according to analysis of communications records. Choi sent the report after confirming that the stern had broken off following the explosion around 9:25 p.m. It is not clear how much information he had at the time.
http://english.chosun.com/site/data/html_dir/2010/04/02/2010040200678.html
 
4) Defense Minister Kim Tae-young said Friday that the more-likely cause of the Cheonan?s tragic sinking was a torpedo attack rather than an underwater mine.
``Both torpedoes and mines are possible causes of the sinking. But I believe that there is a higher chance that torpedoes were the cause,?? Kim said at a National Assembly session.
http://www.koreatimes.co.kr/www/news/nation/2010/04/116_63550.html
 
 
 
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jhpigott       4/2/2010 10:04:57 AM

?developments? = not so thinly veiled reference to the Cheonan sinking??

Senior U.S. diplomat visits Seoul to discuss N. Korea

SEOUL, April 2 (Yonhap) — A senior U.S. diplomat met with South Korea?s top nuclear negotiator and other security and foreign policy officials here on Friday for discussions on what he called important ?developments? in the region.

?It was important, given the developments, to come (to Korea) for a chance to talk? with officials in Seoul, Assistant Secretary of State Kurt Campbell said at the start of a meeting with Wi Sung-lac, Seoul?s chief envoy in six-nation negotiations on Pyongyang?s nuclear ambitions.

http://english.yonhapnews.co.kr/news/2010/04/02/0200000000AEN20100402007500315.HTML

 
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Hamilcar    The time of the explosion and the gunfire are definite.   4/2/2010 11:32:50 AM
Its the sinking time that skips around.

I've explained my estimates for the torpedo calculations. 40,000 meters to cover at a silent creep speed of less than 5 m/s , setup (11 hours travel) to get a torpedo off in about 100 seconds run-time at 20 m/s  (2000 meters chase which means you get within 1000 meters of the target) in an area of swift currents (4 m/s so you have to either account for drift and station keeping because its a  SMALL 300 tonne  boat). That means you have to maneuver close to the island beach shelf. Even if  I stipulate 6000 meters chase run , again, launch has to be  within 3
 
http://upload.wikimedia.org/wikipedia/commons/thumb/6/69/Baekryong_location_2.svg/800px-Baekryong_location_2.svg.png" width="706" height="506" /> 
         
 
 
This is not a friendly place for subs or even semi-submersibles. I don't see how that place as wired as it is could be a safe transit zone especially with the currents for anything operating on battery at creep speed (sub). The semi-submerged speed boats use ICE motors and frankly not able to use two tonne or 1 tonne torpedoes.
 
H.
 
 

 
 
 
 
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Hamilcar    The time of the explosion and the gunfire are definite.   4/2/2010 11:39:34 AM
Gagh! Hit the send button before complete...
 
Its the sinking time that skips around not the gunfire or the seismic episode.

I've explained my estimates for the torpedo calculations. 40,000 meters to cover at a silent creep speed of less than 5 m/s , setup (11 hours travel) to get a torpedo off in about 100 seconds run-time at 20 m/s  (2000 meters chase which means you get within 1000 meters of the target) in an area of swift currents (4 m/s so you have to either account for drift and station keeping because its a  SMALL 300 tonne  boat). That means you have to maneuver close to the island beach shelf. Even if  I stipulate 6000 meters chase run , again, launch has to be  within 3000 meters of the island.
 
http://upload.wikimedia.org/wikipedia/commons/thumb/6/69/Baekryong_location_2.svg/800px-Baekryong_location_2.svg.png" width="706" height="506" /> 

Baengnyeong Island is in Red.

 
       
 
 
This is not a friendly place for subs or even semi-submersibles. I don't see how that place as wired as it is could be a safe transit zone especially with the currents for anything operating on battery at creep speed (sub). The semi-submerged speed boats use ICE motors and frankly not able to use two tonne or 1 tonne torpedoes.
 
H.
 
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VelocityVector    H.   4/2/2010 3:04:55 PM

Re depth charges.  According to reports, at least two Cheonan sailors were casually texting friends and family right before the incident.  That would be unusual if Cheonan or local friendlies were busy prosecuting a suspected contact with depth charges at the time.  Other reports indicate the skipper was in his cabin. 

If Cheonan had simply rolled a depth charge off her stern while steaming ahead, the geometry suggests she would have avoided the hammer unless the charge had armed at a very shallow depth and since the skipper would have had modern fathometers at his disposal he never would have authorized such a criminally-inane depth setting.  Don't the latter marks of US depth charges provide for a minimum detonation depth, which should have given Cheonan time to avoid the hammer? (I believe the answer is "yes.")

If Cheonan had projected depth charges they would have been launched from the stern and not in a forward arc given the ship's layout and likely projector placement.  This would tend to preclude the possibility that Cheonan ran over her own projected charge.  If Cheonan did steam over her own projected charge, she would have to been maneuvering hard, which is not really conducive to the casual text messaging reported. 

If Cheonan steamed over another ship's charge, the Cheonan would have been operating pursuant to coordinated tactics devised over many years to avoid friendly fire incidents with depth charges and also to maximize the possibility of registering a hit on target.  She would have been well aware that a proximate ship was using live ordance and taken steps to reduce the danger.  The other ship would have coordinated with Cheonan and taken steps to reduce the risk of blue on blue.

Considered, it's more likely that Cheonan could have taken the hammer of another ship's depth charge than a case where Cheonan had maneuvered over its own charge; however, especially at night and in 40 meter water, the Cheonan would have been informed in advance that a local ship was tossing live ordnance and buttoned-up accordingly.  I believe this is inconsistent with the reports of casual text messaging and a skipper in the cabin.

The firing pistols of depth charges are designed to be robust given how they are likely to be handled in rough seas, under maneuvering conditions, stored, managed by young conscripts formerly, etc.  Which would tend to make an onboard premature detonation by a depth charge unlikely even if the ordnance was relative vintage.  Do the South Koreans keep powerful, radically dated ordnance aboard their vessels?  (I don't know but I doubt this; depth charges are easy and inexpensive to manufacture new and, unlike battleship powder charges, do not depend on WWII-era propellant grain technologies and firing tables for accuracy.)  If a depth charge did prematurely explode on Cheonan's deck, survivors should have smelled it while abandoning ship.  If a depth charge prematurely exploded inside Cheonan, survivors should have observed secondaries.  Immediately following rescue, some of Cheonan's sailors communicated information before they were gagged.  None of this information indicates that the survivors detected the smell of an explosion or witnessed secondaries.  Just a single bang and then a bifurcated hull in short order.

I am open to a depth charge scenario, but not at all convinced.  More importantly for now, it's not sexy enough ;>)

v^2

 
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jhpigott       4/2/2010 4:08:51 PM
Another accident/coincidence??  How bad are the seas right now in the Yellow Sea??
 
 Fishing boat missing after searching for sailors from sunken ship

(ATTN: UPDATES with more details at bottom)
SEOUL, April 3 (Yonhap) -- A fishing boat has vanished and is feared to have sunk after searching for sailors missing from last week's naval disaster, maritime police said Saturday.

Police said they lost contact with the 99-ton boat, carrying nine people aboard, after receiving a distress signal at around 8:30 p.m. Friday in the area off the western sea border with North Korea, where the patrol ship Cheonan ship sank on March 26.
 
 
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Reactive       4/2/2010 5:28:29 PM
Depth charges are armed by pressure & timer, in addition to being thrown astern, there are 3 failure modes needed to explain a water hammer depth charge effect, it's by no means impossible, but the odds are slight that a depth charge would a) drop off the side without properly being propelled, b) arm without pressure sensitive switch, c) override time switch, depth charges are very simple weapons, but to detonate under the ship requires quite a lot of failure, the fuses are designed robustly to avoid this.
 
It's definitely possible, but I see it as less likely than a torpedo attack, simply because of the failure modes needed to explain depth charges, and the fact that at the very least, the captain would be aware, and presumably have communicated his intent. If they knew it was unintentional detonation of a depth charge they would probably  be more cautious about raising the possibility of NK involvement, and at the very least, we would see the process of "hung out to dry" in action already. 
 
It's (to me) 70 percent likely to be a red torpedo, and 30 percent likely to be an accident involving blue munitions, I'm skeptical about the probabilities of the latter happening because of the safety mechanisms incorporated in the fusing of such munitions, as well as the fact that no captain worth his salt would launch charges without travelling at a fair rate of knots and having a target that was several hundred feet below.
 
Despite their explosive charges, for very obvious reasons, such munitions rely on double or triple redundancy, it's not impossible but unlikely, in my view, and at the very least it makes the presumption that there is an overt cover up taking place, which I think is unlikely. I think they're just waiting for consultation and some form of strategy.
 
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Hamilcar       4/2/2010 6:52:27 PM
 
The US Mark 9 is a WW II fast sink design that has been somewhat modernized.
 
 
 
H.
 
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Reactive       4/3/2010 11:38:27 AM
Defense Minister Kim Tae-young said yesterday he thinks a torpedo attack is the more likely cause of the sinking of the Navy patrol ship Cheonan.

During a question-and-answer session on emergency matters at the National Assembly in Seoul, Kim said a torpedo attack and a sea mine blast were the two most likely causes of the tragedy, but he put more weight on the idea of a torpedo attack.

Kim?s response followed a question by ruling Grand National Party lawmaker Kim Dong-sung, who inquired which of two possible causes - torpedo or mine - was more likely.?In case of a torpedo attack, either the weapon can hit the ship directly or it can explode right below the vessel and create a bubble jet effect [a type of underwater explosion] to break the ship,? Kim said. ?The picture of the cut sections seems like it had been hit by a torpedo directly.?

Kim said that?s why the severed section of the Cheonan?s bow was shaped like the letter ?C.?

The Defense Ministry made public Wednesday recorded footage by a thermal observation device showing the bow of the sunken Navy ship.

Kim said that a seismic wave detected at the time of the explosion was consistent with the blast of a North Korean torpedo.

The Korean Institute of Geoscience and Mineral Resources detected the seismic wave of 1.4 to 1.5 magnitude underwater when the Cheonan was presumed to have ripped in half.

Such magnitude is equivalent to an explosion of 170 to 180 kilograms (374 to 396 pounds) of TNT.

The minister added that a marine who recorded the footage with a thermal observation device on Baengnyeong Island, which was near the explosion in the Yellow Sea near the inter-Korean border, saw a type of water column that erupts after a torpedo blast.

Meanwhile, military rescue divers resumed an underwater operation in search of 46 missing crew members from the Cheonan yesterday.

The rescue mission, which was suspended for two days since Wednesday due to strong winds and high waves, resumed around 11 a.m., according to the Joint Chiefs of Staff in Seoul.

?A total of 54 and 48 divers have implemented an underwater mission at the submerged rear and front sections of the ship, respectively,? said a defense official on condition of anonymity. ?For the rear part, divers went down three times between 10:41 and 11:38 a.m. Other divers for the bow part also dived three times between 10:55 and 11:48 a.m.?

The seismic wave is consistent with a minimum explosive equivalent of 400lb of TNT - the MK-9 seems to generally have a explosive weight of 200lbs, I will accept that if the warhead was PBX this could still near the 400lb TNT equivalence. To my knowledge this isn't the case though.
 
I also wonder whether the MK-9 would have had necessary improvements in pistol fusing safety, It still seems that for one to go off under the ship there would need to be (or would be presumed to be)
 
a) A mistake as to sea-floor depth
b) An order to release munitions
c) A problem with firing these
d) A problem with fusing.
e) Usually these are launched in volleys from both sides of the ship (is that the case with the Cheonan?) to maximise the coverage of overpressure, given there is only one seismic event reported it would have to have been the very first charge that failed, and I find this unlikely in a strictly probablistic sense.
 
I am sure it's not impossible by any stretch of the imagination, but I feel that at the very least we would have been told by now that the Captain had given the order to use these weapons, and I can't see them as being much use against semisubmersibles. All the reports I've seen, (and I accept we are reliant on these pieces rather than the full picture) points to genuine surprise as to the explosion, I think if the captain was in shallow water releasing depth charges he'd have long-since been thrown to the wolves.
 
I think the seismic event, as people have stated, is more consistent with the warhead size expected on a light torpedo carried by a semi-submersible assuming that the explosive mix has not been radically changed over time.
 
They should be able to prove the negative re: depth charges though, as they will be obviously surveying the munitions/magazines.
 
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