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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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Reactive       4/8/2010 1:22:15 PM

Thanks,

 

So at 40kts the target's position is a semicircle of radius of roughly 420m (assuming 20s for projectile flight time). Very poor kill probability assuming that they're not setting a dead-straight course.


 
That is the reason for plotting a track solution and for use of a rapid fire gun. Its an interesting problem as you have to solve for a vector (direction and speed) then beat the area of ocean that you predict the future contact position will be after time of flight. 20 seconds gives a semi-circle as you say of roughly 400 meters assuming a 20 m/s rate of advance. So you lay down a barrage wall of shells in front of the target. Effective air burst radius for 3 inch HE/frag would be about 15 meters radius (lethal). As a rough rule of thumb, I would beat at least 15 shells into the track once I got a shoot solution. That would be six seconds to lay down a ladder on a vector of 120 meters length, not 400 meters. The provisional object target I estimate at least to be to be 10-15 meters long which which means a five second turn moment at 15 degrees arc second. at 10 m/s before the hull loses bite and skids. A track solution should be possible and a PK of maybe 30%-50% is possible? Certainly that straddle salvo would be possible, and the crew of the speculated object target would sweat for it.

Very interesting, the significant thing being that "they" weren't by any means home-free the moment "they" started their dash... I.e. if it was part of a preplanned strategy, it wasn't one without significant risk of being uncovered. (especially if there was airpower in the area, which I still find very odd...).
 
Problem is that if it was sneaking out at 2 m/s, and it was 90 minutes after the attack? 4800 seconds would mean 9600 meters separation, but if we assumed the object hung around to make sure Cheonan sank and allowed only 3600 seconds at creep 2 m/s speed to evade? 7.2 kilometers separation and then its tracked, solved, shelled, uses countermeasures and speeds to safety? That would mean about 300 seconds dash to safety or 6000 meters at 20 m/s. The Soc Cho would have ~  60 seconds of R/U ammunition to use in ten such straddle solutions and could use both of her mounts to bracket the track to handle target turn right or turn left off solution.

I don't see that as a problem, but rather a good fit.
 
2m/s might be at the high end of possible "quiet" velocities in those waters, it's obviously the engine noise/rpm that governs the detectable thresholds rather than the specific speed through the water, whilst fighting powerful currents this power can't be increased without increasing the acoustic signature, one would assume that the velocity could be anywhere between 1 and 2m/s.. We also have to guess as to whether they loitered, the fact that there was a spyplane later on could have been to see whether the Bow of the Cheonan had also sunk...  In any case, I can't see them needing to loiter very long given what we know about the speed of the sinking..

At the very least, nothing is ruled out.
 
 

And if this is the primary mechanism that the Cheonan would use to engage targets these distances then the semi submersibles could be exploiting a gap in the effective engagement envelope of fast maneuvering targets with this class of patrol vessels..



That would be between direct lay and indirect lay, or about 4500 meters.  


 

I can't figure out the lack of air-support in the area after the sinking though, especially given the reports of a NK spyplane in the vicinity... No additional info of that as far as I'm aware... And none on the initial reports of 4 returns...

 

That I don't know.  

Perhaps general confusion, lack of effective co-ordination...
 

H. <
 
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Reactive       4/8/2010 3:49:00 PM

More Footage of Shipwreck Revealed

An investigation team of the Defense Ministry on Wednesday revealed additional video footage filmed using a thermal observation device at the moment the Navy corvette Cheonan sank in the West Sea on March 26.

http://english.chosun.com/site/data/img_dir/2010/04/08/2010040800459_0.jpg" title="" alt="In these grabs from a night-vision video clip released by the Defense Ministry on Wednesday, the stern of the corvette Cheonan on the left is sinking fast compared to the slowly sinking bow on the right. /Courtesy of the Korean Navy" /> In these grabs from a night-vision video clip released by the Defense Ministry on Wednesday, the stern of the corvette Cheonan on the left is sinking fast compared to the slowly sinking bow on the right. /Courtesy of the Korean Navy

There are three sequences. In the first, shot between 9:02:26 and 9:02:29 p.m., the ship travels normally. In the second, between 9:22:38 and 9:23:39 p.m., the stern begins going to sink quickly while the bow lists 90 degrees, after the bow and the stern are clearly separated. Then the stern disappears from the screen in just a minute. In the third, between 9:23:40 and 10:07:23 p.m., the bow goes under.

The additional footage was discovered by the joint civilian-military investigation team during an inspection of the video surveillance system of the Sixth Marine Brigade.

At guard posts equipped with a night vision, video clips are recorded only when a duty soldier pushes the start button, but the camera at headquarters automatically records clips.

A ministry official said, "We had not received any report about this latest footage but the investigation team dug them up. Nothing was recorded before 9:22 p.m. because the soldier operating the camera did not aim it at the Cheonan at the time."

Earlier, the ministry revealed footage showing the stern listing sideways, which was filmed at a guard post on Baeknyeong Island for about 40 minutes from 9:23:46 p.m. right after the explosion on the ship. At the time it denied there was any more footage.

 
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Reactive    english.chosun.com/site/data/html_dir/2010/04/06/2010040600350.html   4/8/2010 4:08:30 PM

Lawmaker Points to Signs Linking N.Korean Sub to Shipwreck

A lawmaker has pointed out that one North Korean submarine was unaccounted for in the West Sea around the time when the South Korean Navy corvette Cheonan sank on March 26. Kim Hak-song, the chairman of the National Assembly's Defense Committee, on Monday said, "Two North Korean Shark-class (325 t) submarines disappeared from our military surveillance between March 23 and 27, but the military authorities have still failed to find out where one of them was on March 26."

Kim was speaking to reporters after receiving a report on the sunken ship from the military.

"It was discovered that two Shark-class submarines left and returned to a North Korean base at Cape Bipagot [in South Hwanghae Province] six times on March 23, three times on March 24, but only once on March 26. But I heard that it's impossible to find out how far the submarines went underwater and what they did," he said. "On March 26, one submarine was found to have exchanged communications with the base at Cape Bipagot from a nearby area but the other was unaccounted for."

The defense minister in an emergency National Assembly session last Friday said two North Korean submarines were unaccounted for around that time.

The military has no evidence that the North Korean submarines infiltrated South Korean waters but believe it is possible that they carried out operations in waters near Baeknyeong Island 50 to 60 km off base, considering that they made only one move on March 26 although they had left and returned to the base several times the previous day.

Kim added the lower side of the Cheonan fell off along the welded seam but the upper side was torn off. "Military officers told me that such destruction is inevitably the result of a torpedo or mine attack."

Military officers told him that the iron plate was 11.8 mm thick when the ship was built and had worn down only 0.2 mm according to a periodic inspection in 2008.

Kim said it is more than 70 percent possible to detect torpedoes about 2 km away at a depth of 30 m, but it's difficult to detect new acoustic torpedoes that slowly chase a naval ship following the sound of the engine. "The military believes that North Korea also possesses such torpedoes," he added.

"As a result of analysis of satellite photos, no semi-submersibles made any movements" around the time of the sinking, he said. "It's difficult for light torpedoes with 50 kg TNT of destructive power carried by semi-submersibles to have torn the Cheonan in two."

 
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Reactive    http://english.chosun.com/site/data/html_dir/2010/04/08/2010040800953.html   4/8/2010 4:26:26 PM

Unanswered Questions Cast Doubt on Military Coordination

A fact-finding committee of civilian experts and military officers probing the sinking of the Navy corvette Cheonan on Wednesday confirmed the disaster occurred at 9:22 p.m. on March 26. At 10:40 p.m., an hour and 18 minutes after the 1,200 ton warship split in half and began to sink, South Korean KF-16 fighter jets lifted off from an Air Force base in South Chungcheong Province. This gap in time has triggered suspicions that there may have been some serious problems in the Navy and Air Force launching a coordinated mission to help the Cheonan. There are also suspicions that the Joint Chiefs of Staff, whose task is to ensure cooperation between the Army, Navy and Air Force, may have been caught off guard.

According to the military, the Second Naval Command was notified of the sinking of the Cheonan at 9:28 p.m., exactly six minutes after it happened. The command ordered the nearest warship -- the Sokcho -- to the scene and requested assistance from maritime police at 9:32 p.m. And at 9:40 p.m., the highest alert level was issued for the West Sea area, which means all Navy vessels must prepare for battle, while Air Force fighter pilots must sit in their cockpits and await launch orders. But it was more than an hour after the Cheonan began to sink that fighter planes lifted off.

The situation at the maritime border with North Korea was extremely tense when the Cheonan began sinking. At 11:00 p.m., the warship Sokcho fired 76 mm cannon for five minutes at an unidentified target that was heading quickly to North Korea. The military said it appeared to be "a flock of birds." The commander of naval operations bypassed the Joint Chiefs of Staff, his direct superior, and phoned Defense Minister Kim Tae-young for authorization for the Sokcho to fire on the target. "The head of the JCS was probably out of reach since he was on a train heading back to Seoul after attending a debate outside the capital," Kim said.

The JCS said its chairman, Lee Sang-eui, was briefed on the situation aboard the train and took "all necessary measures." Really? Lee had attended a debate on combined South Korea-U.S. military strategy in Daejeon, which included high-raking officials from the Pentagon. He boarded a KTX bullet train at 9:27 p.m. after dinner with U.S. military officers and arrived in Seoul at 10:31 p.m. In the end, the KF-16 fighter planes were dispatched 78 minutes after the Cheonan began to sink, and the authorization for the Sokcho to fire was given by the defense minister rather than by Lee.

The investigation of the shipwreck must thoroughly look into the initial steps the South Korean military took just after it happened and discover how much coordination took place between the Army, Navy and Air Force. That is the best way to sharpen South Korea's military response in case a similar incident takes place again.

 
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Hamilcar    Still not enough evidence.   4/8/2010 6:43:56 PM
But we can NOW rule out grounding.
 
We have the two mysteries... if it wasn;'t a speedboat, (and its NOT birds) then what did the Sok Cho engage? 
 
What caused the Cheonan explosion?
 
As to the RoKN command and civil leadership, they seem to have reacted well. It's the rest of the RoK military that appears slow. 
 
H. 
 
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VelocityVector       4/8/2010 7:28:12 PM

We have the two mysteries... if it wasn;'t a speedboat, (and its NOT birds) then what did the Sok Cho engage? 
 

Possibly it was an unarmed diversionary boat, a Taedong, that briefly hoisted a radar reflector and then skedaddled launching decoys once it was confident it had been spotted.  With the sole competent ASW threat, Sokcho, occupied in the wrong direction and screwing up its own detection capabilities with 130 explosions sounding shallow waters, the submarine shooter would have had time to take the long slow path home safely.  Yet another theory, and one that provides for a larger torpedo.

Sherlock^2

 
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Hamilcar       4/8/2010 7:38:39 PM




We have the two mysteries... if it wasn;'t a speedboat, (and its NOT birds) then what did the Sok Cho engage? 

 


Possibly it was an unarmed diversionary boat, a Taedong, that briefly hoisted a radar reflector and then skedaddled launching decoys once it was confident it had been spotted.  With the sole competent ASW threat, Sokcho, occupied in the wrong direction and screwing up its own detection capabilities with 130 explosions sounding shallow waters, the submarine shooter would have had time to take the long slow path home safely.  Yet another theory, and one that provides for a larger torpedo.


Sherlock^2




Then they were brave men, even though evil. Italy makes very good naval guns and the fire control systems that go with them.  

H.
 
 
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Reactive    Re:   4/8/2010 8:09:24 PM










We have the two mysteries... if it wasn;'t a speedboat, (and its NOT birds) then what did the Sok Cho engage? 



 






Possibly it was an unarmed diversionary boat, a Taedong, that briefly hoisted a radar reflector and then skedaddled launching decoys once it was confident it had been spotted.  With the sole competent ASW threat, Sokcho, occupied in the wrong direction and screwing up its own detection capabilities with 130 explosions sounding shallow waters, the submarine shooter would have had time to take the long slow path home safely.  Yet another theory, and one that provides for a larger torpedo.




Sherlock^2











Then they were brave men, even though evil. Italy makes very good naval guns and the fire control systems that go with them.  




H.


 

Or foolhardy, they couldn't have known there'd be no strike aircraft/helis in the area, frankly if there had been it would have been suicide....
 
Perhaps it was in the area to observe, perhaps it didn't get close enough to do so... One thing that does occur to me is that though the initial contact was around 9km away, and possibly signalled a fairly weak semi-sub sized return, I'd bet it wouldn't have been engaged unless it was initially closing, possibly made a turn after the shelling started, there's got to have been a greater duration here than has been explained (enough time for calls to be made, and enough urgency to suggest an "attack"), I think this engagement, from detection to the target reaching the NLL was a lot longer than 5 minutes, in which case it could have been a case of a secondary NK covert observation that didn't get close enough to assess the damage, perhaps making an aerial observation necessary, which would explain the spyplane...
 
And if it was a midget sub that initially made a hit with a slow acoustic-homing torpedo, it could have left the area way before a confirmation of a hit was confirmed (it would want to do so before sonar bouys and ASW aircraft would have shown up), a shot in the dark as it were.. but with secondary assets on hand to act as observation, assets that are fast enough to f-off back home at a rate of knots if fired upon...
 
All speculation (except that I feel damn sure it's a Torpedo), just trying to connect the dots... I think the growing involvement of the USN is interesting, as if they want to be able to issue a categorical proof of this, and leverage as much international pressure as possible without appearing to predjudice the results of the investigation. There seems a good likelihood of recovering casing fragements from a torpedo if they have enough assets searching the seabed... .
 
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gf0012-aust       4/8/2010 8:17:22 PM


There seems a good likelihood of recovering casing fragements from a torpedo if they have enough assets searching the seabed... .

which is why the videorays would be going in before clearance divers.....
 
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VelocityVector       4/8/2010 8:21:48 PM



Then they were brave men, even though evil. Italy makes very good naval guns and the fire control systems that go with them.  

Perhaps comparable to U-boat crews and their inculcated nationalism, that bane of humanity sometimes.

I don't place too much stock in reports that surveillance has accounted for all NorK surface boats in the Baengnyeong area.  The Serbs flummoxed NATO with crude field implemented decoys left and right apparently.  For the price of cheap rubber and plastic the NorKs could similarly head fake our look overs; not so easy with subs but then no nation betrays how its subs are tasked so nondisclosure is accepted practice even with the NorKs, who have not officially denied involvement in the Cheonan event I observe.

As for the Italians, I have worked with and represented Italians in highly advanced technical matters, some military, over nearly two decades.  The Italians can be world-beaters in high technology and mathematics.  Unfortunately my experience also has been that they do not shy away from poaching the solutions of others -- in this respect I would compare them to the Chinese, again based on personal anecdote.

v^2

 
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