Geoff FordenROK Ship: Typical Torpedo Damage

click on the image for a larger version

The two halves of the ROK Ship Cheonan are raised from the sea near the ROK-owned island of Baegryeong-do, which in turn is very close to the DPRK’s mainland. The Cheonan was sunk on 27 March 2010. (Note, I have “flipped” the image on the right to better match up with the front half.)

One of the “mysteries” surrounding the sinking of the ROK’s warship, Cheonan, is that the explosion split the ship in half, a result our popular culture has trained us to forget. After all, World War II movies always show a torpedo strike in the same way: one or two white streaks quickly approaching the ship followed by a localized jet of water where the torpedo struck the hull. Sailors stream out of their bunks to jump over the side as the ship keels over, taking in water. Below the water line, jagged holes, punched by the explosive force of the warhead, let in sea water. Compartments quickly (or if dramatic effect is needed, slowly) fill with water, drowning all the bit players, uh, sailors trapped below.

These movies have influenced our expectations for the damage caused by modern torpedoes even though there are much more efficient ways for a torpedo to destroy a surface ship. Consider the damage done by 200 to 400 kg of high explosive to the hull of the USS Cole. This high explosive was put essentially right beside the Cole’s hull the same way a “classical” torpedo would place it. The damage is considerable, but it is “classical,” in the sense that it is a hole punched in the side. (The damage is considerably greater below the water line, as can be seen by the increased “dent,” because the water increases the coupling between the explosively generated shockwave and the hull.


The hole punched in the side of the USS Cole by between 200 to 400 kg of high explosives in close contact with the hull. Note how the damage is considerably more wide spread below the water line. The terrorist attack on 12 October 2000 caused the tragic loss of 17 crew members and the injury of 39 others but did not sink the Cole.

Significantly more damage can be cause by the same, or even smaller, explosive detonated significantly below the keel of a warship. The destruction of the warship pictured below was caused by the explosion of 44 295 kg of high explosive well below its keel, between a quarter and an eighth of comparable to the explosive that holed the Cole but causing much more damage. Near the start of this sequence, which begins in the upper left corner and then moving right and then down, you see a “spray dome” forming on either side of the ship. This is caused by the initial shockwave of the explosion breaking the water’s surface. Caused by the interference between the upward-moving initial shockwave and its reflection from the surface, it is a region where the water density has been considerably decreased. Considerable damage is caused by this shockwave hitting the ship, as indicated by the plume of black smoke the boiler emitted after being violently shaken when the shockwave was transmitted through the hull. The hull could have been significantly damaged by that same shockwave.


This series of images show the destruction of an Australian warship by a torpedo with 44 295 kg of high explosive detonated well below its keel. The plume rising above the ship’s superstructure is caused by the collapse of a large gas bubble sucking sea water upward in a powerful jet.

The second major effect damaging the hull, and probably the one that caused the vessel to break in half, was a jet of water blasting its way through the ship. This jet was formed as the gas bubble created by the initial explosion collapsed upon reaching the ship’s hull.

This is the way modern torpedoes sink ships. Everything about the Cheonan’s sinking is consistent with either a torpedo or submerged mine blowing up beneath the ship’s keel.

<— A jet of water caused by a bubble bursting at the surface. It is formed as the pressure inside the bubble is suddenly released as it bursts, causing the water at the bottom of the bubble to rush in.

Update The day after I posted this, the South Korean government reached a similar conclusion.

Update (30 April 2010) (thanks to Josh Pollack for pointing this article out!) South Korean scientists at the Sound Engineering Research Lab of Soongsil University have performed an analysis of the acoustic signals (the media report mistakenly calls them seismic waves) associated with the sinking of the Cheonan. It would be very nice to see their actual analysis—and the data would be even cooler—but it appears on the face of it to be a very interesting result. Their main conclusion, again based solely on the media report of their findings, seems to be that the Cheonan was actually struck by a heavy torpedo. (The say the most likely candidate is the Chinese Yu-3 heavy torpedo with a 205 kg high explosive warhead.) According the article, the South Korean scientists believe the torpedo struck the hull of the Cheonan but since the explosive is significantly aft of the torpedo’s bow, the center of the explosion was a little over 2 meters away. They rule out the “kill mechanism” being a bubble jet.

Some of the other statements in the media report are open to more interpretation; again I wish I could see the original report. Apparently, they can hear secondary explosions through out the ship after the initial torpedo detonation. The media report seems to hint that these were caused by the fire associated with torpedo detonation. However, secondary explosions could just as easily—more easily in my opinion—be caused by the heaving of the ship in response to either the shockwave or the rush of water associated with the bubble formation and possible the jet that I think still might have formed depending on how strong the force of attraction due to the hull was to the bubble.

By the way, this standoff distance of a little over 2 meters probably represents the results of a careful analysis to determine the best distance at which to explode a large charge from a ship’s hull. It presumably balances all the effects we have discussed. I recommend people read John Field’s comments in the comments section.

Comments

  1. GreenTom (History)

    Hi…at least according to Wikipedia, that series of pictures is of the HMAS Torrens being sunk by an MK48, which I believe has a much larger than 46kg warhead.

  2. b (History)

    “Everything about the Cheonan’s sinking is consistent with either a torpedo or submerged mine blowing up beneath the ship’s keel.”

    Yes. It is either or.

    But absent any further indication of a torpedo like a sub sighting an old moored contact mine or ground mine which drifted away form its original position due to strong currents in the area may be the more likely explanation.

    I therefore wonder about the title of the piece.

    “ROK Ship: Typical Mine or Torpedo Damage” would be more consistent and less accusing.

  3. Rwendland (History)

    On odd fact about this sinking, which has gone close to unreported in the UK media, is that the location of the sinking was off the opposite side of Baengnyeong Island from the sea border with North Korea (the Northern Limit Line):

    !http://img.yonhapnews.co.kr/etc/graphic/YH/2010/03/29/GYH2010032900120004400_P2.jpg!

    ( taken from this Yonhap News item in Korean)

    Has this been reported much in the US? It seems an unlikely place for an attack, as escape for any attacker would be difficult, seeming to give the loose mine theory more credence.

    NB The BBC has a poorer map, but in English, in this story.

  4. Geoff Forden (History)

    GreenTom

    You are correct that Wikipedia says it was a MK 48, which—again according to Wikipedia—has a warhead of 295 kg. However, according to the Master’s thesis “Investigation of Close Proximity Underwater Explosion Effects on a Ship-Like Structure Using the Multi-Material Arbitrary Lagrangian Eulerian Finite Element Method”, which is an excellent resource for exactly this phenomena (available at http://scholar.lib.vt.edu/theses/available/etd-01302007-141530 ) it was a MK-46, which has the 44 kg warhead I mention. I have no personal knowledge of which was actually used. If any wonk-reader can give an authoritative answer, I would be very grateful. (Unfortunately, both Wikipedia and Masters students have been known to make mistakes!)

  5. Allen Thomson (History)
  6. Geoff Forden (History)

    Thanks Allen! That’s certainly authoritative.

  7. johnbragg

    Retroactively, an argument for blowing up the NK rocket on the launch pad in April 2009.

    If we had, this would be retaliation, and proof of the foolishness of such warmongering.

    We allowed the lauch, and yet here we are.

  8. D

    Huh?

  9. John Bragg (History)

    D:

    Imagine that the North Korean ICBM/satellite test had been disrupted by a Tomahawk missile strike as the rocket was fueling, destroying the rocket itself and a good deal of the launch facility.

    Either the Norks act belligerently because they see no penalty for doing so and indeed reap rewards in terms of aid, or they act belligerently because it is somehow in the nature of their system (implacably hostile/too fractured to impose discipline/erratic and emotionally unstable/etc.)

    If they act belligerently because there is no penalty, then blowing up their rocket might have been a penalty, and might have curbed further misbehavior.

    If they act belligerently because of the nature of their system, then they would have continued their misbehavior.

    But if we had struck the rocket last year, this incident would be widey perceived as retaliation.

    I’m questioning the tendency for such perceptions.

  10. kme

    I’ve been aboard that vessel (the Torrens, not the Cheonan) – it’s somewhat humbling to see the destructive power of a relatively small amount of high explosive.

  11. milton (History)

    The military has ruled out the possibility of a mine, according to the JoongAng Ilbo:

    http://tinyurl.com/2aupt7p (in Korean) The article is titled “Military Rules Out the Possibility of a Mine”

    According to the article, the investigative team has concluded that the explosion was a non-contact explosion (as is being reported frequently today), ruling out the possibility of a stray 1950s-era mine.

    However, the area around Baeknyeong Island was mined in the 1970s when a US radar station was positioned there. There mines were deployed along the island’s north shore. The Cheonan sank off the island’s southwest coast. The currents in that area move north. Most of the mines were removed in the 1980s, but even if one were magically in the path of the Cheonan that night, it would have ran out of power long ago and would be unable to explode (according to the Defense Ministry. The area around where the Cheonan sank is a heavy fishing ground, and the probability a leftover mine would just happen to hit a passing warship is miniscule.

    And there was one. Hypothesis that is. The word going around Seoul now is “North Korean torpedo.” Military intelligence, according to Yonhap, reported to President Lee Myung-bak that the attack was of North Korean origin “with certainty.” Yesterday, South Korean Prime Minister Chung Un-chan, in an address to the nation yesterday, was all set to speak about North Korean involvement in the sinking, but nixed that part of his speech 30 minutes prior to airtime.

    North Korea sympathizers in the South seem to agree with the growing consensus, but are claiming the torpedo was from an American warship. Take, for instance, perennial nationalist nutter-butter Kang Ki Gap, the head of the Democratic Labor Party, an extreme left-wing, pro-North Korea, anti-American nationalistic outfit who declared that he believes that “the Americans know what happened,” and hinted that they were complicit in sinking. In the same breath, he blamed his own government for not turning the Yellow (West) Sea into a “peace zone.” (Gotta love the logic implicit in that).

    See here:
    http://tinyurl.com/23tvket (in Korean)

    At this stage, South Korean investigators know the murder weapon (a North Korean heavy torpedo), plenty of circumstantial evidence placing the North at the scene of the crime (military intelligence from both the US and South Korea), and plenty of possible motives (revenge for the Daecheon Sea Battle, succession crisis, wavering domestic support). All they need now is a few shreds of physical evidence to slam dunk the case.

  12. Chad

    ‘All they need now is a few shreds of physical evidence to slam dunk the case.’

    True, but maybe they don’t want to slam dunk the case. Its going to put them in a very tricky position if they do formally make the link with the DPRK. Sadly there is little they can do in response, so its probably in their interests to leave it as an unsolved mystery. What is retaliating militarily going to do? If they strike some N.Korean vessel in response, a few North Koreans will die – the DPRK might react militarily in the short term (I doubt it would spark a full-scale war), but nothing will change.

    I’d imagine they know full well what caused this already. Unless something gets leaked into the press from someone that does know, then it could be ‘unresolved’ for some time.

  13. anonymous (History)

    Wouldn’t forensics play a big role in attribution? Whether the explosive was a NK torpedo or leftover mine there will be parts remaining, e.g. motor, propulsion device, casing, etc. The water depth at the site is shallow, and salvage divers and robots were in the water almost immediately after the incident.
    If it is a leftover mine, that will be easiest to determine. If the NK bought the weapon from another country that might preclude positive attribution, but if the thing or its remaining parts are provably NK’s then it is a murder weapon admissible in court.

  14. John Field (History)

    Geoff, I see the problem a little differently. Shock waves seem to me to be very impedance mismatched to efficiently do work against the ship’s hull unless it was like steel a couple of feet thick. The hull looks like an almost free-space boundary condition to a shock and therefore the shock wants to deliver energy with too much pressure and not enough displacement to match the load.

    I believe that the issue is just getting the correct standoff distance so the explosive efficiently does work against the ship’s hull. If the explosion is too shallow it vents prematurely. If the explosion is too close to the hull it wastes all its energy pulverizing stuff, pushing explosive gases and water through the ships hull. The hull has a pressure failure strength (which is a decreasing function of applied area) and I think the strategy is to apply that pressure to the widest possible area. (Once things start to break, it may be that the internal structure becomes increasingly susceptible to further damage at declining pressures too.)

    Figure the desired applied pressure is probably around 100 psi and approximate that most of the explosive energy goes into a roughly adiabatically expanding bubble and not into the initial shock. For 295 kg explosive, that will happen when the bubble grows to about 3 m diameter. The dynamical pressure of the moving water will be comparable out to maybe another bubble radius or so distance. So, I’d expect a standoff of about 3 m ~ 10 feet would be about right and a detonation depth of maybe twice that to contain the bubble (assuming the ship draws enough water to meet the aforementioned standoff condition beneath the keel).

    Once you’ve blown a 6 m (~20ft) diameter hole in the bottom of the ship and driven 100 tons of water moving upward at 100 mph through the gaping hole, sure the ship can break in half. By comparison, in the USS Cole explosion, the venting time of the explosion was limited to the air sonic transit time across the hole size of the blast ~ 20 milliseconds or so, not enough to get a big slug of water moving into the ship, and the energy is wasted.

    To me, this does not seem inconsistent with Keith Webster’s discussion, although the emphasis is different.

  15. Geoff Forden (History)

    John,

    I don’t think that we disagree. However, the shockwave does do damage. This can be seen, I think, by the boiler venting dark smoke at the same time the shockwave is causing cavitation at the surface of the sea. My guess is that caused by the acceleration the entire ship. Plus the shock differential, if you will, caused by the increased shock energy transmitted by the bulkheads etc. (Which probably increase the effective coupling between the sea and the ship’s structure.)

  16. Azr@el (History)

    This is a bit dated, but recalling my grandpa’s geriatric comrades drone on about their boring ass ww2 stories; a torpedo causes maximum damage when it detonates at depth below the center of mass a vessel. This results in a type of nautical jujitsu, instead of using the explosive power of the warhead to directly act against the vessel, the warhead instead displaces the water underneath the keel, causing gravity to snap the vessel in half. The initial blast and collapse of the displacement bubble help to weaken and ensure separation, but gravity is the real killer.

    Unless the ROK Navy found actual evidence of a torpedo, I’ll reserve judgement. The damage effect of a mine snapping the keel of a vessel and a torpedo doing the same are identical. As far as the likelihood? Hmmm, if you had to wager your home, your car and god forbid even your IPad, where would you place your marker; on the skill of DPRK sub crew to land a perfect blow with a torp against a modern vessel with SONAR or the random blind luck of an acoustically invisible mine in old naval war zone?

  17. Geoff Forden (History)

    Azr@el

    I don’t believe that is the case. The torque put on a ship when it is in heavy seas is (probably) greater than caused by gravity when the two ends are suspended at its two ends and most ships live through that.

    However, I have heard that theory before. I think that theory might originate from the bubble intersecting ship’s hull but before people realized that a jet was formed.

  18. Rwendland (History)

    This Korea Times story claims the investigators are considering the type EO-3G torpedo, built by China in the 1980s, as the probable culprit. The article states that the EO-3G is a “Passive Homing” torpedo with 12 km range. It also lists, with brief specs, three other types of heavy torpedo NK is claimed to have.

    Googling for EO-3G torpedo does not show up any more info about this torpedo, which is strange. However the story says “capable of hitting a ship after tracking the vessel’s screws acoustically”.

    The site of the sinking is about 20 km from the NLL, so any submarine launching an EO-3G would have to be well within the South Korean side of the line.

  19. George William Herbert (History)

    Ah, something unambiguously up my alley…

    With my Naval Architect degree hat on:

    No, the bending moment caused by heavy seas is less than that which would be encountered if you suspended the ship by the ends. If you try to pick a ship up like that you will break its back at the center very rapidly. There are very good reasons that ships in drydock or under construction have support all along the keel; a large one is that bending moment, and to a lesser degree shear force, is a big deal. It has to be relatively evenly distributed.

    The basic worst case wave load is a wave with wavelength (peak to peak) about equal to the length of the ship (technically, usually length between perpendiculars, the point on the bow at the waterline to the point where the rudders hang, though LOA (overall hull length) may be more appropriate for some load scenarios).

    You take the basic water wave equation and plug in that length, it gives you wave height (crest to trough). You take that, you superimpose for two worst case limits with crests at the ends and trough in the middle (called sagging, for the center sagging down with the trough), and for the case with the crest amidships and the troughs at either end (called hogging, for the deck arching up like a pig’s back).

    Then you figure the distribution of buoyancy along the ship’s hull for that wave shape, what level it will be sitting at with displacement equal to weight, and that gives you the input loads to figure out the bending moment on the ship as a whole, in conjunction with weight distribution (structure and payload, if any).

    That’s the pseudostatic simplification; in reality you need to consider pitching behavior as well, the ship climbing up waves and diving down into troughs, but the first thing you calculate is the pseudostatic approximation.

    Only very rarely do you get any part of the bottom exposed. Picking up the ship by its ends is far worse than that…

    Ships are designed for reasonable loads. Small ships are simply overmatched by large mines and torpedos; you can’t build enough strength in to realistically survive them.

    I am not terribly familiar with the detailed explosion dynamics of under-keel detonations; never studied the gas bubble / pressure dynamics of that in depth.

    I do know that this effect has been known for a long time – the faulty US torpedo fuzes in WW 2 were magnetic fuzes intended to run under and detonate under ships, for example (though the backup mechanical impact fuzes also had a defective too-weak firing pin, so we were out of luck entirely at the outset there).

  20. anon

    Just out of curiosity. What are the parallels for an underwater nuclear explosion like Test Baker (Operation Crossroads) or Operation Wigwam?

  21. John Field (History)

    It seems to me that I am making at least two distinct and testable predictions which would be observably different from Geoff’s explanation.

    1) Damage to ship will be significantly greater if the explosion is something like 10 charge diameters away from the hull rather than right up against it.

    2) The precise symmetry of the explosion is relatively unimportant. Efficient concentration of the energy into a jet requires the bubble to be quite symmetric. For example, if the explosion were two half-charges spaced two or three meters apart this would have a major effect on the jetting, but I claim that it would have little effect on the ship damage.

    Generally, I would heuristically divide “shock wave” effects to be those necessarily associated with the compressibility of water – e.g. acoustic phenomenon in both high and low pressure limits. “Bubble effects” by contrast can be analyzed with entirely incompressible water. This is, naturally, a somewhat arbitrary distinction.

    In this view though, the soot emerging from the exhaust stack is simply due to the bottom of the ship being forced upward and compressing the internal volume of the ship at a relatively light pressure – like 100 psi and low speed – like 100 mph – rather than as a shock wave propagating into the ship at extremely high pressures and thousands of meters per second.

  22. Bruce Klingner

    Geoff, Here is a blog I wrote based on my meetings in Seoul this week.

    It is becoming increasingly obvious that a North Korean torpedo caused the March 26th sinking of a South Korean naval ship. The Cheonan, a 1200 ton corvette, was severed cleanly in half, a characteristic of torpedo attack rather than a naval mine. Seoul has already ruled out an internal explosion, running aground, or other accident as the cause.

    My discussions with government officials in Seoul this week revealed uncharacteristic reticence and nervousness. South Korea is now like a CSI investigator who, upon seeing a dead body with a bullet hole in the forehead refuses to rule out a heart attack as the cause of death since the only suspect in the room with a pistol is a vicious gangland boss. Better to engage in a lengthy investigation, both to gather irrefutable evidence and to delay the inevitable day of reckoning.

    Everything in South Korea is on hold pending the outcome of the investigation. Government contacts are reluctant to be drawn into discussions of hypothetical policy responses. Some newspapers, public organizations, and legislators have called for a strong response but have yet to gain traction with the populace whose mood is predominantly one of mourning.

    It appears the public is angry, but not angry enough to advocate military strikes against North Korea that could escalate into an unpredictable all-out conflict. At this point, it appears unlikely for Seoul to contemplate a military attack. There is repeated precedent for both South Korea and the US not responding militarily to previous North Korean attacks, even when they resulted in loss of life.

    All of that could change, however, upon the final conclusion of the ponderous investigation. Ironically, Seoul appears concerned by both potential outcomes, namely either too much or too little evidence. A clear verdict of North Korea’s finger on the trigger could inflame the public to demand a stronger military response than either Seoul or Washington would be comfortable with.

    Conversely, strong suspicion but a lack of irrefutable evidence will constrain Seoul’s policy options. South Korea will contemplate both unilateral actions, including punitive economic and diplomatic measures, as well as taking the issue to the UN Security Council for multilateral response. In the latter case, Seoul would face stiff opposition from China and Russia, which have obstructed previous attempts to punish Pyongyang for violating UN resolutions.

    If South Korea is reluctant to attack, it would be impossible for the US to be “more Korean than the Koreans” by advocating stronger measures. But the Obama administration should consult closely with the South Koreans and support whatever action they are comfortable taking. This should include pressing the Chinese and Russians to relent in favor of tougher international sanctions, and taking unilateral punitive action that complements the South Korean approach.

    Some South Koreans were sharply critical of Secretary of State Hillary Clinton’s recent comment that she hoped there would be “no action or miscalculation that could provoke a response that might lead to conflict [and] the way to resolve the outstanding differences among [the Koreas was] to return to the six-party talks framework as soon as possible.”

    This value-neutral, even-handed approach to North and South Korea when Seoul was clearly the aggrieved party resurrected memories of Secretary of State Warren Christopher’s insulting 1996 comment calling upon both Koreas to show restraint after North Korean special forces killed 10 South Korea citizens.

    All told, the Cheonan crisis is taking place at a time of very solid bilateral relations between the US and South Korea. The strength of this alliance contrasts sharply with Washington’s troubled relationship with its Japanese ally. A united US-Korea response to North Korean provocation underscores the value of alliance with the U.S.

    One wonders how the US-Japanese alliance would respond today to a similar crisis.

  23. Daniel (History)

    My question is that, while the damage suffered by Cheonan could be explained by torpedo attack, there are other evidences which contradict this.

    1. The observation crew on board did not observe any water jets when the ship sunk. It is somewhat improbable that the torpedo attack which could sink the warship in half does not leave any observable evidence.

    2. And corollary to this, surviving crew did not suffer any internal organ damage likely caused by such a big explosion. They heard a loud bang, but not to the extent where it could hurt them. It is questionable that the explosion which could break the ship in half, leaves the ship crew relatively intact. (Other crew who died seemed to have drowned)

    3. Ship’s sonar crew did not observe any incoming torpedo. (The defense minister stated that the likelyhood of sonar crew missing the torpedo could be around 30% in such a rough weather.)

    There are other stuff people are arguing about – but these are what comes to my mind now. Again, I think torpedo attack is one of the most probable cause. However, there are weakness in the theory as well as strength. My biggest question is how can the crew of the ship miss what hit them if it is sunk by such a huge water jet? All the pictures & videos I have seen suggest it would be nearly impossible for the navy crew to miss such a torpedo hit. And if the explosion / water was not big enough to be observed by the crew, then could it break the ship in half?

  24. George William Herbert (History)

    Re to Daniel –

    Regarding who saw what…

    You would have to talk to every survivor, find out where they were in or on the ship, and what they saw.

    The depth of detonation, size of warhead, position of detonation relative to hull centerline, breadth and depth of the hull, and other factors would determine how much disturbance broke the water’s surface.

    It’s likely that there was some, but possibly nobody was looking towards it who survived. Most crew on modern warships are well and truly inside most of the time – no view outside, not on deck – and most observers would be on the bridge and looking out and forwards, not back.

    Re internal inuries –

    By the time the effects of external underwater explosions penetrate the ship, the dynamics are that of rapidly moving pressure fronts and not shockwaves per se. As John Fields pointed out, the velocity of the fragments of the bottom of the ship is highly subsonic. Internal injuries among surface ship crew from underwater explosions are rare.

    Regarding whether this was an underwater explosion or not –

    This is relatively unambiguous. The damage pattern on the raised fore and aft parts of the ship is clear. How big, how far away, what it was (torpedo or mine or what) is not yet entirely clear.

    The South Korean government has a lot of information we don’t yet, including all the survivor interviews, plus physical access to the salvaged ship hull. They don’t have any good motivation to overstate the evidence here – I don’t think them marching to war with North Korea is in their national interest.

    Re not hearing the inbound torpedo –

    Again, SK has more info than we do, including details of sea state and water conditions, thermocline, etc. Someone familiar with the torpedos could give a prop blade count, rpm, sound profile analysis, find out what the acoustic signatures look like and how well the characteristic frequencies propagate under the exact conditions at sea that day.

  25. Bruce Klingner

    re: Ship’s sonar crew did not observe any incoming torpedo. (The defense minister stated that the likelyhood of sonar crew missing the torpedo could be around 30% in such a rough weather.)

    i talked with a senior defense official in Seoul this week who said the Cheonan’s sonar was actually not very good.

  26. Daniel (History)

    Thanks guys for answering some of my questions. It is often difficult to get a clear picture from rampant speculation that is going on Korean Media. Reading from Korean forums, there are considerable amount of skepticism among Koreans- especially against whatever military says. (And I can’t say they are blameless – they have a long track record of covering things up.) Korean media also seem to be mishandling it as well – often they themselves are the source of many of these rumours(ranging from suicidal human torpedo to Russian Shkval torpedo)…

  27. Nanonymous

    It can be surprisingly difficult to ascertain the source or extent of damage in action, particularly if the ship never makes it back to a yard for repair and analysis – Bruce Loxton’s excellent book “The Shame of Savo” (written by a survivor of the sinking of HMAS Canberra at the Battle of Savo Island) devotes a great deal of discussion to the whole question of whether Canberra was actually torpedoed at the height of the action – something that you would think would have been imposible to miss.

  28. J.E. Dyer (History)

    Just a note — very late to this discussion — on the acoustics of the event referenced briefly in the original post.

    It is easily possible to detect a torpedo making its run at a target with the use of even low-sophistication passive sonar. A torpedo is one of the least “confusable” underwater noisemakers. Its rapid increase in RPM and short running time are very distinctive. Torpedoes’ acoustic signatures are also distinguishable one from the other by type.

    If the South Koreans have an acoustic record indicating a torpedo coming at Cheonan, that’s definitive. Mines make no noise of that kind.

  29. Pat Flannery (History)

    Even a acoustic record of a incoming torpedo isn’t impeccable; we (the US) use CAPTOR mines that lie on the bottom and release a torpedo upwards toward a ship passing overhead that their sensors detect.
    Unless South Korea can find something that is unimpeachable in regards to a torpedo hitting the ship (say a gyro system or torpedo props) Occam’s razor suggests the ship passed over some sort of influence fuzed mine that detonated under it, generating the same sort of damage a torpedo detonating under its keel would.
    A big problem with the torpedo attack scenario is that it implies that either a surface vessel fired it without that being detected, or a sub fired it with neither the sub or the incoming torpedo being detected.
    Although NK minisubs may be hard to detect, how big of a torpedo can one carry? It took a considerable amount of explosives to break the ship in half, more in line with what full-sized sub’s torpedo would do.
    My favorite wild press theory of the moment is that it was a NK suicide minisub loaded with explosives that sailed under the ship’s keel and blew itself and its crew up in best Japanese Kamikaze tradition from 1945.

  30. Mitch (History)

    Maybe it’s too late to add something to this post but I couldn’t pass by this one cuz I’m korean(south) and closely following the event every day. Ironically enough, informations are very limited in the country where the ship sunk. Only wild assumptions and scenarios are spreading through both pro-gov and anti-gov medias and perople are divided sharply between so called torpedo-group and accident-group. I can see that you guys, who don’t have to consider political aspect of the situation and , are ruling out the possibility of an accident. But we have our reasons to suspect what the gov announces.

    First of all they lied about unmistakable basic facts such as the time and location of the sinking. Can you believe this? They said it was 22:45 and then changed the time for three times and fixed it only after three days when the acoustic record, which was reported to the authority the day after the sinking, came out at last to the media. And the location? Well we are not 100% sure even now about the exact location of the hit(if it were a torpedo attack). They never fix the exact location. KNTDS was online so they couldn’t miss the situation of the ship during the fateful time of 22:12~22 26th, march.

    More than that, they told media that TOD was not recorded at all at first. And then a local media found out that there actually was a video recorded aroud the time of the sinking. Only after that the gov reluctuntly released videos only before and after the actual the sinking. They’re saying that the sinking itself was never recorded. My, my what kind of TOD records the situation only before and after? Maybe crews in the ship could missed the water blow caused by a torpedo, but TOD can’t….

    And regarding the communication records, they say it’s all classified record and can’t release it to the media. Even though they revealed every detail of military communication records after YeonPyung naval engagement(2002, 6 casualties for SK). Ok. maybe it’s classified now. But initial communication records with the ship and the naval police clearly says that the ship is suffering from flooding and are using the term “stranded”. And there were some family members of the dead crews who said some crew members told their families that “Something’s wrong here. I can’t talk to you now.” with celluar phone in 22:16, which is 6 mins prior to the announced sinking time. Can you guess what the gov said about this? They told the media that there was a normal reception checking communication by 22:19 using commercial radio line. What kind of navy ship uses commercial radio line during their mission? And if everything was going all right before the hit, why they don’t just release that part of military communication record?

    These questions are just a tip of the icebrg and mysteries regarding the sinking are growing everday. We have an big election in 2nd June and the conservative ruling party is already notorious with using so called “northern wind” to preoccupy the political agenda with security issues, like George Bush did after 9.11. I can’t help but find uncanny resemblance between two events. Unfortunately in this case, I’m not even sure if it were actually an attack.

    I’m not denying the possibility of the torped attack. Actually it’s the most probable theory with limited information. But if you look closely into the situation, there are too many lies, concealment, and political opportunism around the unfortunate ship and its crew.

  31. cenoxo

    The dotted waterline that you’ve indicated on the photograph of the USS Cole is the post-attack waterline after the ship had settled several feet down by the bow (to the left in your photo). You can see this bow-down angle more clearly here and here.

    The true pre-attack waterline at which the surface level explosion occurred is the top edge of the darker anti-fouling paint area that extends downwards and covers the lower half of the Cole‘s hull.

    Judging by the height of salvage crew members walking on the deck of the Blue Marlin recovery vessel, the true waterline is about four or five feet lower than your dotted waterline (meaning that the Cole was sitting this much higher in the water when the blast occurred). This waterline more closely matches the wider diameter of sub-surface blast damage on the hull.

    More photos at Haze Gray & Underway – USS Cole.

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