The Cheonan Incident: Skepticism Abounds

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By Peter Certo, Greg Chaffin, Hye-Eun Kim

On the night of March 26, 2010, the South Korean naval vessel ROKS Cheonan split in half and sunk.  Forty-six sailors lost their lives.  In order to determine the cause, the South Korean government created the Joint Investigation Group (JIG), with representatives from the United States, United Kingdom, and Sweden, among others. The JIG has since issued its findings in stages, culminating with the release of the official report on September 12, 2010, concluding that a torpedo fired by a North Korean submarine sank the Cheonan.

Despite the JIG’s goal of providing definitive proof of the cause of the incident, public skepticism has only increased. Indeed, opposition politicians, professors and several media outlets have expressed doubt in the conclusion advanced by the official report. In a poll commissioned by Seoul University’s Institute for Peace and Unification Studies, only 32.5 percent of South Koreans expressed confidence in the report’s conclusions.

There are several sources of public skepticism, particularly from the scientific community. Furthermore, the secretive attitude adopted by the Lee government, its heavy-handed approach in dealing with the incident, and its reluctance to address or even allow for questions or concerns have served to fuel skepticism and allowed for conspiracy theories to abound. This annotation will address the pros and cons of the various theories behind the Cheonan’s sinking.

The Cheonan incident remains a point of tension between North and South Korea. But the international community and the South Korean public can play a role in defusing this potentially dangerous situation.

The Official Report vs. Alternative Theories

The bulk of the official report focuses on supporting the conclusion that a North Korean torpedo sank the Cheonan. It analyzes the explosive composition and residue, compares the recovered drive shaft with North Korean torpedo schematics, and models the underwater explosion, shockwave, and bubble effect and subsequent damage to the Cheonan.

Skeptics have subjected this narrative to several probing questions. For instance, why was the drive shaft of the recovered torpedo relatively undamaged, and why wasn’t the No. 1 mark that identified the torpedo as North Korean in origin burned off?

The report asserts that the No. 1 marking was written prior to exposure to salt water, “since salt was precipitated on the marking and corroded interior ink was found to be risen above the ink.”  The marking was made with an anti-corrosive paint, helping to explain its condition.  Furthermore, expert analyses of underwater temperature change find that although the water temperature at the time of explosion was 3,000 degrees C, the temperature would drop to 28 degrees C within 0.1 second.  As a result, “heat transfer would not occur all the way to the rear and thus no significant change in temperature would have resulted in the area where the marking is written.”

Second, the report posits that the battery section of the torpedo (4.125 meters long) acted as a shock absorber, shielding the propulsion section from the blast.  Moreover, the shockwave created by the explosion would have immediately pushed the propulsion section backwards a distance of 30-40 meters, thereby limiting its damage.

If not a North Korean torpedo, then what might have caused the ship to sink? Alternative theories abound. The ship ran aground. It collided with another ship. It experienced an internal explosion. Or it hit a mine.

Proponents of the theory of grounding point out that the area around Baekryong Island, with its shallow water and reefs, is too narrow and dangerous for safe passage of a  submarine. Second, the SOS issued by the Cheonan stated the ship had “run aground.” Finally, scratches on the lower side of the hull and damage to the ship’s propellers are consistent with grounding. Damage to the blades suggests that the Cheonan reversed engines, attempting to free itself after running aground.

The official report considers the possibility of grounding but argues that the damage sustained is not consistent with such a scenario. Furthermore, the characterization of the fracture surface did not reveal traces of large plastic deformation caused by loss of longitudinal strength consistent with grounding. Other indicators of grounding, such as broken blades, global scratch marks, or damage to the sonar dome were absent. Damage sustained by the propeller blades was determined to have been caused by inertia due to the sudden halt of propeller rotation. Finally, the report confirms that there are no reefs in the incident area.

The hypothesis that ROKS Cheonan collided with another ship was largely laid to rest when the USS Columbia, considered the likeliest other party to a collision by some alternative theorists, returned safely to port in Hawaii. Despite claims by skeptics Jae-Jung Suh and Seunghun Lee that the angular damage to the Cheonan’s hull seems “more consistent with a collision with a hard object” than with the bubble effect of an explosion, the report does not address the possibility that a collision may have occurred with any other body than a ship. Suh has further argued that, contrary to common reports that the Cheonan was split in half, it actually broke into two larger pieces as well as a third smaller piece. He argues that the damage on the larger hull pieces as well as the pattern of breakage may be the result of a collision with a small submarine or unexploded torpedo.

In addressing the possibility that the Cheonan collided with another ship, the report cites the lack of a bow impression amid the damage, the dearth of debris that could have been left by another ship, assertions by KNTDS (Korea Naval Tactics Data System) and AIS (Automatic Identification System) analysts that no other ships were within 5.5 miles of the Cheonan at the time of the incident, and finally a lack of supportive crew testimony. The report concludes that there is “no possibility” that the Cheonan collided with another ship. Its authors did not find it necessary to model or simulate what such a collision might have looked like.

The report also dismisses the various theories of internal explosion, for instance, from the 40 or 76 millimeter ammunition contained in the forward and aft magazines. The damage sustained by the Cheonan does not support this possibility. The location of the magazines does not correspond to the break plane. Furthermore, there were no physical indicators of an explosion originating in any of the ship’s magazines. There was no outward bending of the hull or the decks, and traces of soot, fire, or fragments indicating an explosion were absent. No damaged or exploded ammunition was found and no relevant injuries to crew members (such as burns) were observed.

The report refutes the theories proposing a fuel tank explosion or engine failures as the cause of the sinking. The fuel tanks are located behind the diesel engine room (aft) and in front of the gas turbine room (mid-ship).  Neither fuel tank exhibited signs of an explosion. There was no outward bending of hull plating around the tanks, nor any damage on either the upper decks or the fuel tank bulkheads. There is also no evidence of fire or damage to the fuel pipe, and crew members did not report either a fire or a fire column. Finally, on the recovery of the Cheonan, neither aft nor mid-ship fuel tanks exhibited substantial damage. Remaining fuel was recovered from both the tanks and the site and determined to be in relatively good condition.

The gas turbine room, meanwhile, sustained significant damage, with a portion of it breaking away from the rest of the ship. The bulkheads surrounding the gas turbine room as well as the decks above were heavily damaged. The gas turbine room is located in the middle of the ship, along the break plane.  However, other physical evidence, most importantly the inward bending of the hull and the lack of traces of fire or fragmentation damage, point away from a gas turbine explosion.  In particular, in an explosion, the turbine blades would fragment and damage nearby walls.  No such damage was evident. Finally, at the time of the incident the Cheonan was operating at low speed (6.7 knots), and therefore the gas turbine engine was not in use.

According to a final alternative theory, the Cheonan encountered an underwater mine. The official report does speculate that an underwater mine would carry a sufficient payload to cause the damage observed. But no fragments were found embedded in the hull or in the surrounding area. Furthermore, tidal currents would significantly affect the depth and position of moored mines, making them at best, an unreliable system.  The report also cites a lack of evidence indicating a contact explosion, such as heat scoring, impact zone, or explosive fragments.  Additionally, numerous fishing vessels traverse these waters and have never encountered mines.  Indeed, during its patrol, the Cheonan itself passed over the site 10 times without any prior incident.  Finally, no vessels involved in rescue and recovery following the incident reported observing or coming into contact with any underwater mines.

Problems and Questions Persist

However, the official report is by no means exhaustive in countering all alternative claims and answering all questions.  Indeed, there are several inconsistencies and omissions that cast doubt on the veracity of the report and on the conclusion it advances.

Such omissions include serious treatment of the “pillar of white light” observed by lookouts on Baekryong Island.  Many have pointed out that a torpedo would not produce such an effect.  The report concludes that this was a water plume but does not elaborate further, and this assertion is not corroborated by the testimony of the survivors. Indeed, the Lee government has generally restricted access to the surviving sailors.  Public access to the survivor’s full testimony has also been similarly restricted, creating further public doubt over the official version of events.

Also conspicuously absent from the report is any explanation as to why no other fragments of the torpedo were found.  Evidence typically associated with a torpedo attack includes fragments of the torpedo embedded in the hull of the ship.  However, no such fragments were observed or collected either from the ship or the surrounding area.  Only the telltale drive shaft and motor of the torpedo were found. It remains possible that the strong currents in the area carried other fragments away or sufficiently hid them, but no such explanation as to their absence is offered.

Questions have also been raised over discrepancies regarding the time the incident occurred.  The initial time of the incident was announced as occurring at 21:45.  This was subsequently revised to between 21:20 and 21:30, before fixed at 21:22.  Furthermore, according to KNTDS, the Cheonan was still moving at 21:25, three minutes after being attacked.  These discrepancies are not mentioned in the report but have been a source of public skepticism.

Finally, any discussion regarding the failure to detect the enemy submarine or the torpedo is absent from the final report. A possible explanation might be that sonar equipment is much less reliable in shallow, choppy water or near underwater rock formations, such as the area in which the incident took place. In such conditions, sonar capabilities can be reduced by as much as 60 percent, greatly decreasing its chances of detecting enemy action.  However, no such explanation is offered, and indeed, the report doesn’t address the Cheonan’s failure to detect enemy action.

There are also several inconsistencies within the report itself that are not addressed.  Chief among them is the difference in the conclusion that the torpedo carried an explosive charge between 200-300 kilograms (depending on depth), later averaged to 250 kilos, and the simulations used to model the incident that used a range of charges from 250 to 300 to 360 kilos of TNT (at depths of six, seven, and seven to nine meters respectively), with each producing similar results.  The simulation suggests that an underwater explosion similar to the one modeled sank the Cheonan.  However, almost all of the simulations pictured in the report model a 360 kilo explosion at a depth of seven meters, and it is not clear that the simulated damage is as great as actually occurred. This is particularly troublesome given the discrepancy between the charge size in the conclusion (250 kilos) and the charge size in the simulation (360 kilos).  The report does not show any simulations that model different charge size and depths.

Finally, Jae-Jung Suh and Seunghun Lee dispute the Investigation Group’s assertion that the aluminum oxides found on the ship and torpedo is evidence of explosive residue. For the aluminum oxide to be the result of an explosion, they counter, the ratio of the oxygen atoms to aluminum atoms should be 1:0.2.  Instead it is 1:0.9, which is a common ratio of a different type of aluminum oxide altogether: rust.

The Cheonan Political Game

Determining the culprit behind the Cheonan sinking requires sorting through a sea of complex computer models, advanced metallurgy, and doctorate-level ballistics. But the incident must also be understood within a political context.

South Korean President Lee Myung Bak’s Grand National Party (GNP), a conservative party that has assumed a hawkish posture toward the North, swept into power in 2007 in a landslide victory over the faltering center-left Democratic Party (DP). But a series of developments battered Lee’s party and damaged its credibility. These included controversial Cabinet appointments, the unpopular opening of Korean markets to American beef producers, a crackdown on an eviction protest in Seoul that left six people dead, controversial handling of public works projects, efforts to remove a “leftist” Jogye Buddhist monk, and the acquittal of the embattled former Prime Minister Han Myeong-sook from the previous Roh administration. As a result, the GNP found itself confronting a wave of anti-incumbent sentiment in advance of South Korea’s regional elections.

Within this context, Cheonan skeptics and government critics have argued that Lee’s party has  exploited the Cheonan sinking to pursue a cynical brand of national security politics. The May 20 release of the JIG’s preliminary report coincided with the official start of the local government elections campaign. It also came just three days before a national first-year commemoration of the late President Roh Moo-hyun’s suicide that would serve as an emotional flashpoint for Lee’s opposition. The May 20 date appears even more suspect given the apparently rushed nature of  the report’s findings.

Lee’s government moved quickly thereafter to file or threaten defamation charges against leading figures who questioned the government’s findings, doubted a link to North Korea, or proffered alternative explanations. The government’s urgent and decisive actions against even reputable skeptics left little doubt that the GNP had hitched its political fortunes to the official Cheonan narrative, whatever its other merits or deficiencies. There was even talk of the GNP rolling back hard won democratic gains in the country. In response, even as some GNP leaders urged the de-politicization of the issue, GNP Chairman Chung Mong-joon told a radio interviewer that, “The Democratic Party and leftists, who have made a number of remarks that seem to stand up for North Korea, protect it and defend it, are people who should be taking as much of the responsibility as North Korea’s leader Kim Jong-il.” The Korea Times called these sorts of tactics the GNP’s “red scare.”

Consequently, many observers predicted electoral successes for the GNP. With nearly 4,000 local races to be contested, 16 in particular – big-city mayoralties and provincial governorships – were considered key, and of these many thought the GNP could win at least nine.

The actual results came as something of a shock. With 54.5 percent voter turnout, the highest in 15 years, opposition parties dominated most races up and down the ballot. While the GNP narrowly held onto Seoul, they suffered a surprise loss in Incheon (the jurisdiction where the Cheonan sank) to Song Young-gil, a fierce Lee critic. All told, the GNP claimed victory in just six of the 16 key races. Analysts widely regarded the results as a rebuke of Lee’s post-Cheonan posturing. Most notably, subsequent polling has revealed a major generation gap in South Korean sentiment, with younger South Koreans less likely to blame North Korea for the sinking and wary of the Lee government’s aggressive response. Although a majority of South Koreans continue to identify North Korea as the likely culprit, more than 60 percent are at least somewhat skeptical of the inquiry’s findings, indicating the level of mistrust in Lee’s government.

Fog over Pyongyang

The key to any convincing indictment of North Korea must be a plausible, rational motive. Unfortunately, as with virtually any study of the isolated regime, it is difficult to verify such speculations.

But the speculation itself is not so difficult, particularly when one contextualizes the Cheonan incident within a longer narrative of Northern aggression. Victor Cha at CSIS has compiled a short list of the most prominent theories of North Korean motivation for an attack. The alleged attack might have been…

  • A “disproportionate retaliation for a November 2009 clash in the West Sea that led to the loss of two North Korean lives [though estimates vary],”
  • A “form of coercive diplomacy trying to force the conservative and nonengagement-inclined ROK government into negotiations in which North Korea could extract aid and assistance,”
  • A “form of ‘swaggering’ to demonstrate to South Korea and to the region its recent efforts at enhancing its naval capabilities,”
  • A “manifestation of internal leadership turmoil in Pyongyang and the pursuit of a hard-line external policy.” Notably, U.S. Secretary of Defense Robert Gates has lent credence to this theory.

None of these scenarios seems inherently implausible. But the snag in the arguments that North Korea sank the Cheonan in a bid to “send a message” to Seoul or Washington, or perhaps especially to stabilize the Kim regime, is that North Korea has steadfastly denied responsibility for the incident in its official proclamations, even threatening “all-out war” should South Korea use the accusation as a basis for retaliatory measures. Perhaps North Korea overplayed its hand and has subsequently sought to avoid any repercussions for an act of aggression. But this would be a change from previous tendencies to explain aggressive behavior as retaliation for South Korean provocations or to claim victory where other parties see defeat. The very magnitude of the incident, which would be the deadliest act of aggression since the 1953 armistice, could even threaten the regime’s very survival, which, as sophisticated Korea watchers have always noted, is its one overriding imperative. Short of an attempt to consolidate the regime’s power as it prepares for succession (which would not exactly lack precedent), it is hard to see how an order to attack the Cheonan could have emanated from the top. The perceived irrationality of the attack has even led to the speculation that rogue elements within the military may have carried it out.

In the end, the regime’s utter lack of transparency has allowed hawkish and conspiratorial interpreters alike to mold North Korean motives to whatever the narrative demands.

U.S. Foreign Policy Objectives

The United States has endorsed the response of Lee’s government and made clear its continued security guarantee to South Korea. The United States has enhanced its commitment by leading the charge for broadened sanctions on the North and participating in conspicuous joint military exercises in the Sea of Japan.

The Lee government’s initially rigid insistence that North Korea would have to acknowledge and apologize for the Cheonan incident before any further diplomatic steps could be taken might have jeopardized the Obama administration’s goal of re-instituting the six-party talks in Northeast Asia. But such fears have appeared to dissipate as some South Korean officials have suggested that the issues are not linked.

Relatively secure in this regional goal, U.S. support of its South Korean ally has also facilitated South Korea’s reluctant cooperation in sanctioning the Iranian regime and rewarded it for its renewed commitment to the U.S.-led effort in Afghanistan. The incident has thus provided an opportunity to strengthen U.S.-ROK relations in light of continued tensions with Japan over the location of U.S. military bases in Okinawa.

China, North Korea’s lone ally, has sought rather unsuccessfully to avoid the issue by refusing to comment on it. Any overt acceptance by the Chinese of North Korean complicity in the sinking would severely narrow its diplomatic options. But China also stands to jeopardize its economic ties to the South and its desired reputation as a regional stabilizer by idling on the issue. Russia, meanwhile, claims to have determined that a sea mine caused the sinking but has refused to share its findings with South Korea. It is likely seeking to maximize its diplomatic leverage with all concerned parties by concealing the extent of its knowledge.

Moving Forward

South Korea’s official report on the sinking of the Cheonan represents a serious effort to bolster the South’s account of the incident and to rebut the claims of skeptics. Many of its answers are well reasoned and persuasive, but as we have made clear here, its final report hardly puts the issue to rest.

Fundamentally, the report is a political document meticulously crafted to lend scientific credibility to the aggressive posturing of the Lee government in South Korea. Whereas a scientific paper might be subject to peer review and critique, the GNP’s forceful crackdown on dissenters leaves no illusions about the document’s political nature. Given lingering questions about the account and its obvious value to the country’s conservative government, Professors Suh and Lee have even wondered aloud whether some of the government’s evidence was fabricated.

The Lee administration has stated that North Korea must acknowledge and apologize for sinking the Cheonan before relations resume.  However, given North Korea’s interest to deny culpability, coupled with continued public skepticism, it may be in South Korea’s best interest to rethink its current position and attempt to re-engage North Korea diplomatically along with international partners.

Indeed, the Lee government may have limited its own options, at least in the short term.  By adopting a strong posture in the face of the North Korean threat, and indeed prosecuting those who have questioned it, Lee has clearly attempted to capitalize on the North Korean bogeyman to prolong its hold on power.  However, this strategy seems to have backfired, as evidenced by the rebuke of Lee’s “pressure approach” toward the North in the last elections.  It is unclear what the South seeks to gain by continuing its hard-line approach.  Furthermore, given predictable Northern intransigence, the Lee administration’s response has left it bereft of other constructive options.  Forging ahead on its current path runs the risk of sparking further conflict.  Such tactics do not have a good track record of success, nor will they likely be conducive to re-engaging the North diplomatically.

In the months ahead, public disapproval coupled with North Korean refusal to acknowledge responsibility, may induce the Lee administration to make a more realistic appraisal of its current approach.  In the interim, South Korea will likely continue to press the international community to censure the North, although China will likely block any such attempt.  Then, after a period of posturing to convince others and itself of its strength, South Korea will probably pursue a more diplomatic approach.  Indeed, the South is already softening its stance with a recent shipment of much-needed food aid to the North.

Despite some movement, tensions remain high.  It falls on the international community and the South Korean public to ensure this incident does not engulf the peninsula in a more serious conflagration and to help facilitate the move back toward reconciliation.

Peter Certo and Greg Chaffin are interns with Foreign Policy In Focus. Hye-eun Kim is a contributor to Foreign Policy In Focus.


Foreign Policy in Focus (FPIF) is a “Think Tank Without Walls” connecting the research and action of more than 600 scholars, advocates, and activists seeking to make the United States a more responsible global partner. It is a project of the Institute for Policy Studies.

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