Another Look at the Cheonan Incident


As relations between the two Koreas worsen, the sinking of the South Korean corvette Cheonan continues to be a significant source of contention. On May 20 of this year, the South Korean-led Military-Civilian Investigation Group (JIG) announced the results of its investigation, charging that a North Korean submarine had torpedoed the vessel. Since then a number of commentators have pointed out numerous flaws in the investigation’s conclusions.

The report itself, however, remained secret, and the world public was expected to take the JIG’s conclusions largely on faith. Unable to dampen down widespread skepticism of the JIG’s findings, the South Korean government finally released its report to the public in September. That was not the original report that was issued in May. South Korean investigators took into consideration some of the public criticisms and attempted to address them in the final version. [1]

I first wrote about the sinking of the Cheonan in July [See: The Sinking of the Cheonan and its Political Uses]. The issuance of the final report since then seemed to call for a re-examination of the evidence, as has the coming to light of some new pieces of information.

The first impression one gains from reading the JIG’s report is that it makes a stronger case for its argument than the previous approach of keeping everything under wraps. As a result, it does appear that a non-explosion cause for the Cheonan’s sinking can probably be ruled out, as can that of an internal explosion.

Upon closer examination, many of the old questions remain, however. I will not detail the points I made in my previous article on the subject, as those mostly still stand. [2] Instead, I will focus primarily on what is new.

In its preface, the report claims that the JIG “took into consideration every single possible cause of the sinking.” That is not quite the case, as the group continues to ignore a rising mine as a possible cause. The primary focus of the report is in proving that a non-contact explosion occurred and that the Cheonan had neither run aground nor collided with another object. In that goal, the JIG has mostly succeeded, although it is still true that not all of the evidence is consistent with any of the conceivable scenarios. Having narrowed the possibilities down to an external explosion, the report persuasively demonstrates that the damage was consistent with a non-contact blast below the Cheonan’s hull. No contact mine or contact torpedo could have caused damage of this nature. With that task accomplished, the report thereafter focuses on attempting to prove that a torpedo was responsible, specifically the one whose components were found on the seabed.

Of particular interest is the examination of the deformation to the hull. U.S. investigators on the JIG determined that the explosive charge would have had to be in the range of 200-300 kg. In its report to the UN, South Korea claimed that “numerous simulations of an underwater explosion” had shown a detonation of an explosive charge in that range. The North Korean CHT-02D torpedo, it pointed out, has “a net explosive weight of up to 250 kg,” thereby falling within the range estimated by the U.S. team. [3]

But in reading the released report, it turns out that the U.S. team did not base its estimate on “numerous simulations.” Instead, it “analyzed the seismic and acoustic waves detected” at the time of the explosion and conducted a visual examination of damage to the hull. [4] South Korean investigators took that data and conducted a simulation, in which the team was able “derive a result within a limited period of time.” That is, the team rushed the test to meet a pre-election deadline. Single simulations were performed for explosive charges at three levels: 250 kg, 300 kg and 360 kg. [5]

The results of the simulations, however, do not back the claim of an explosive charge in the range of 200-300 kg. In preparing the final report, the JIG performed further simulations, including a broader range of explosive charges. [6]

At 250 kg, the test “partially match[ed] the actual damage.” [7] The diagram of the simulation damage at 250 kg indicates that the phrase “partially match” is stretching language to the point of meaninglessness.  A side-by-side diagram contrasts the sharp and severe upward damage to the hull of the Cheonan and its complete split in two, against the small rift in the bottom and mild dent on the sides in the simulation result. [8]

Only at the 360 kg charge did equivalent damage occur in the simulation. [9] That result presented a problem, which the JIG solved by a fudge, now declaring that the explosive charge was in the range of 250-360 kg. The upper limit was what matched the evidence. And the lower limit was included because the goal was to attribute the sinking to a North Korean CHT-02D torpedo, which carries a maximum charge of no more than 250 kg, even though that level was incapable of causing the kind of damage the Cheonan suffered.

What about a sea mine? Three types of mines were analyzed: bottom, moored and floating mines. Contact floating and contact moored mines were ruled out given the nature of the damage. As for a non-contact moored mine, the JIG pointed out that the brisk current and widely varying tide difference in that area made their use ineffective. The stronger the flow, the more the tether would angle closer to the sea bottom, bringing the mine farther below the surface. Furthermore, the depth of water in this area varies by a range of four meters due to tides. The Cheonan that day was zigzagging through the sea and, the JIG claims, it had patrolled “near the incident site at least more than ten times,” thus indicating “that there were no prior mine installations.” [10] However, that conclusion would only be valid if the Cheonan had precisely followed the same path on its last round that it had on one of the previous occasions, and if currents had remained the same throughout. No anchors or mooring devices were discovered on the seabed, which the JIG adduced as additional evidence for dismissing a moored mine as a potential culprit.

For the most part, these are valid points, but no mention was made in the report of rising mines, which lie on the seabed and thus are unaffected by currents or changing tides. As a ship approaches, they launch upwards and explode a few meters below the hull, creating damage that is consistent with that seen on the Cheonan. And given that the North Korean CHT-02D torpedo did not carry a strong enough charge to be responsible for sinking the Cheonan, that may indicate a mine as a more likely cause. As the JIG report admits, “A non-contact torpedo detonation causes identical damage as a non-contact mine detonation.” [11]

South Korea had placed sea mines in precisely this area, and these had been connected by cable to land-based controls. But in 1985 the mines were deactivated by removing their detonation cables and control boxes. The mines themselves remained on the seabed. It was not until two years ago that an operation was launched to gather them up, “resulting in successful recovery of 00 munitions.” The number is an obvious typographical error, but even had an actual number been quoted, no indication is given as to whether or not all of the mines were recovered. One technical expert has “argued that the detonation cable, when cut and exposed to seawater, can induce voltage…which then can ignite the electric detonator.” When he measured the electric current, he found the detonator to be “sensitive enough to explode.” Other experts disagreed. At 47 meters depth where the Cheonan sank, any mines at that site would be too distant to inflict much damage, especially given their weak 136 kg explosive charge. [12]

Russian investigators, however, noted that a fishing net was entangled around the Cheonan’s propellers and speculated that the ship might have caught the net, which in turn brought up a mine from the bottom. The South Korean mines had initially been installed close to shore, at a depth of 7 to 10 meters. Could it be that at one point the Cheonan sailed too close to shore, as the damage to its propellers hints? Even so, the explosive charge in these mines is too low, unless perhaps several were grouped together. It seems, however, that it would take an unlikely combination of factors for these particular mines to have been responsible. That said, none of the other suggested alternatives appears all that likely either.

Six small fragments of aluminum and aluminum alloy found in the wreckage of the Cheonan were compared with the torpedo components. It was judged that an explosion would have broken down any fragments into minute pieces, but of those it had, the “JIG was not able to identify any fragment that was actually used in the torpedo.” [13]

Although the evidence strongly points to a non-contact explosion creating a bubble jet effect splitting the Cheonan in two, there is one striking anomaly. A bubble jet forms a powerful column of water rising about 100 meters into the air, and it is this that tears a ship apart. No one on deck could miss such a dramatic sight, yet no survivors witnessed a water column. Many were below deck, asleep at the time of the incident. But there were those who would not have missed it. An officer on bridge duty reported, “I did not see any light, flashes, flames, water pillars, or smoke.” Nor did a sentry on the starboard bridge wing see a water column. And neither the sailor steering the vessel nor the sailor on duty at the portside bridge saw a water column. Two land-based sentries, located 2 1/2 kilometers away, heard a loud sound and saw a bright flash of light. One of the sentries claimed to see a column of water, although one wonders if he was prompted to say that, given that the incident occurred shortly before 9:30 PM on March 26, when it would have been rather dark. Furthermore, weather conditions at the time were 40 percent fog, 78 percent moonlight and a visible range of 500 meters. [14] A flash of light would have been seen from shore, but it is doubtful that the sentry could have seen a column of water at that distance under those conditions. And it would have been odd indeed for this eagle-eyed observer to spot what those onboard the Cheonan failed to see.

Considerable attention was paid to the spectroscopic analysis of materials adhering to the Cheonan and the torpedo components. Simulations indicated that white powder adhering to the ship and torpedo “were confirmed to be explosion products formed by the detonation of an underwater explosive formulation with aluminum. They were not corrosion products of aluminum.” [15]

Some independent analysts have pointed out that the spectroscopic readings more closely match a type of clay, unrelated to an explosion. One of the things I looked for in the report was the pattern of the adhered materials, as presumably deposits resulting from an explosive force would show a pattern that differs compared to those adhering to metal that had settled in mud on the sea bottom. But that aspect is unaddressed in the JIG report.

The general distribution of the white powder does seem rather odd in some cases. For instance, the JIG report says that “an enormous amount of white powder was also observed on the inner and outer platings of the stack.” [16] One wonders if powder resulting from an explosion could have been so heavily deposited in the interior of the smokestack.

Bolstering the claim that the white substance is clay deposit, last month a Korean journalist discovered a broken piece of a clamshell, covered in the same white substance, wedged inside the propulsion system of the found torpedo. That would seem to prove that the white material adhered to the surface of the torpedo only after it had been sitting on the sea bottom. The clamshell would not have been stuck in the torpedo prior to the explosion. [17]

Professor Chung Ki-young of Andong National University examined actual samples and determined that the substance was amorphous basaluminite, otherwise known as gibbsite, and could only have been built up over an extended period of time. [18] That was the same conclusion that Korean-American physicists Seung-Hun Lee and J.J. Suh had reached, based on their analysis of the spectroscopic readings.

It is interesting to note that while traces of HMX, RDX and TNT explosives were found on the Cheonan, investigators found no explosive residue on the torpedo components, as confirmed by General Yoon Jong-sung, head of the military’s Criminal Investigation Command. [19]

While the release of the JIG report has brought a welcome increase in the amount of information available, the evidence is still inconclusive. A torpedo cannot yet be ruled out as a possibility, but the torpedo that was located can be eliminated as the culprit. It should also be noted that the Cheonan was equipped with sonar, which was actively monitored, and at no time did it detect a submarine or a torpedo. In many ways, the evidence remains perplexing, failing as it does to point to any definitive conclusion.

The JIG’s determination that a North Korean submarine fired a torpedo at the Cheonan does not convince. Nevertheless, the South Korean government of Lee Myung-bak has not hesitated to condemn North Korea for the tragedy, using the incident to create friction with its northern neighbor. That contributed to generating an atmosphere that led to the armed clash at Yeonpyeong Island, and now the South Korean government is threatening to conduct air raids on the North.

South Korea conducted the JIG investigation with the participation of its allies. Aside from a minor role played by the Swedish team, there was no impartial, let alone countervailing voice in the JIG. Too much in the JIG’s investigation hinted at a predetermined conclusion, with the evidence being made to fit. It would serve not only the cause of truth but that of peace for a new investigation to be opened, with the participation of all interested parties, including North Korea. Such an investigation will not happen, of course. The Cheonan’s tragedy is too useful in the Lee Administration’s campaign to kill the Sunshine Policy of his two predecessors.

[1] Ministry of National Defense of the Republic of Korea, “Joint Investigation Report: On the Attack Against ROK Ship Cheonan,” September 10, 2010.


[3] Joint Investigation Report, p. 30

“Letter Dated 4 June 2010 from the Permanent Representative of the Republic of Korea to the United Nations Addressed to the President of the Security Council,” June 4, 2010.

[4] Joint Investigation Report, p. 147-149

[5] Joint Investigation Report, p. 150-153

[6] Joint Investigation Report, p. 154

[7] Joint Investigation Report, p. 256-260

[8] Joint Investigation Report, p. 152, Figure III-5-9

[9] Joint Investigation Report, p. 169, p. 190

[10] Joint Investigation Report, p. 84-87

[11] Joint Investigation Report, p. 93

[12] Joint Investigation Report, p. 96-102

[13] Joint Investigation Report, p. 130-132

[14] Joint Investigation Report, p. 132-141

[15] Joint Investigation Report, p. 261-288

[16] Joint Investigation Report, p. 269

[17] Kwon Hyuk-chul, “Clamshell Covered in White Substance Discovered on Cheonan Torpedo Fragment,” Hankyoreh (Seoul), November 5, 2010.

[18] Bae Ji-sook, “KBS Program Raises Questions About Cause of Cheonan Sinking,” Korea Times (Seoul), November 18, 2010

[19] Jung Sung-ki, “Seoul Reaffirms North Korea’s Torpedo Attack in Final Report,” Korea Times (Seoul), September 13, 2010