hankyoreh

member of the civilian-military joint investigation group (JIG)

By Kwon Hyuk-chul, Staff writer

The Ministry of National Defense released a full report Monday on the findings of the civilian-military joint investigation into the sinking of the Cheonan. The civilian-military joint investigation group’s (JIG)report concludes that the Cheonan sank due to an underwater explosion caused by a CHT-02D sound-guided torpedo fired by a small North Korean submersible. This was the final report of the JIG examining the Cheonan’s sinking.

Overall, the content of Monday’s announcement was roughly the same as the JIG findings announced on May 20. As was the case in May, the report stated that the Cheonan “sank when its hull was bisected by a shock wave and bubble jet effect resulting from the underwater explosion of a torpedo, and the location of the underwater explosion was three meters aport from the center of the Cheonan’s gas turbine room at a depth of six to nine meters.” Likewise, both announcements stated that the weapon system was confirmed to be a CHT-02D torpedo with 250kg of high explosives, manufactured and used by North Korea.

The report also reaffirmed the JIG announcement that the samples of noncrystalline aluminum oxide discovered on both the hull and a torpedo propulsion device found in the waters near the scene of the sinking had the same ingredient, a component of underwater explosives. The report maintained the previous conclusion that there was “no possibility” that the sinking resulted from the vessel running aground or suffering metal fatigue, as was suggested by some experts.

Although the report provides explanations of the JIG’s investigation findings over a five-month period, observers are charging that it fails to dispel suspicions that have been raised since the sinking, as it merely repeats the previous answers on questions raised since the May 20 announcement, without providing any clear explanation.

To begin with, the report was unable to prove that the ink used to write the “No. 1” on the torpedo propulsion device was North Korean-made. This writing, presented as “conclusive evidence” for the torpedo explanation, has been the subject of continued debate. Citing military confidentiality, the JIG did not respond to calls for it disclose a torpedo export catalog that reportedly includes specifications of the torpedo in question.

The report also failed to resolve the contradiction between the explosive force of the “No. 1 torpedo” and seismic wave data. The final report included the findings of a simulation in which the explosive force of the torpedo was raised from its initial estimate, but this created an even larger discrepancy from the force of a seismic wave that was detected the day of the Cheonan’s sinking.

The Ministry of National Defense included in the final report the findings of simulated explosions at depths of seven and nine meters where the explosive force of the “No. 1” torpedo had been increased to the equivalent of 360kg of TNT. Based on the experiment, the ministry stated that it “obtained a result that was more similar to the condition of the Cheonan when 360kg of TNT exploded at a depth of seven meters.” It added that the simulation involving an explosion at a depth of nine meters gave a “weaker” result relative to the condition of the Cheonan.

However, these results increased the discrepancy with the seismic wave data. When converted into its TNT equivalent, the force of the 1.5 seismic wave that arose at 9:22 p.m. on the evening of the sinking amounts to only 140 to 180kg.

The main topic of debate has been the “double bending” observed with the Cheonan’s starboard-side propeller screw, which bent inward with its edges bent back outward, as this is the area where the “explosion” explanation makes the least sense. Experts noted that the explanation of the double bending given by the defense ministry Monday was inadequate to dispel questions.

The Defense Ministry has changed stories several times on the double bending of the propeller screw. At first, it claimed that it had become bent when it came into contact with the ocean floor while the Cheonan’s stern was sinking. At the time of the May 20 announcement, it said that the propeller bent due to “rotational inertia” as it stopped abruptly, presenting simulation results to back this explanation up. However, the simulation used extreme values, for example by having the Cheonan traveling at the ship’s full speed even though it was actually moving at its normal speed of 6.7 knots at the time of the incident, and the screw only bent slightly.

Perhaps conscious of these criticisms, the Defense Ministry added an explanation about transformation due to “axial intertia” in its announcement Monday. According to this explanation, the starboard gearbox was pushed about 10 centimeters as the engine stopped due to the explosion, and due to the abrupt shock, similar to the impact of a baseball bat, the screw’s axis was also pushed out and became bent as it stopped abruptly.

However, the axial inertia explanation does not give a clear account of the double bending in the screw.

First, the explosion occurred on the port side, but the actual bending of the screw happened on the starboard side. It would stand to reason that the screw would be more heavily damaged on the left side, closer to the point of the explosion, rather than the right side, which was farther away.

A number of experts are also saying that if an underwater explosion massive enough to sink the Cheonan had occurred, the hull and crew members would have suffered a far greater shock than has been observed. Given that injuries to surviving crew members have been relatively light and that all of the sailors who perished have “drowning” as their presumed cause of death, observers say questions are likely to continue over whether the Cheonan actually sank due to an underwater explosion in the neighborhood of 360kg of TNT, as per the Defense Ministry’s announcement.

In addition, in its final report Monday the Defense Ministry used the term “dwarf submersible” to refer to the vessel that attacked the Cheonan, rather than referring to it as a North Korea “Yono class submersible.” Analysts say this is likely to stem from continued questions over whether the Yono submersible actually exists.

D&D Focus Editor-in-Chief Kim Jong-dae said, “The final report is actually a step backward from the early report.”

“They are saying an arrow was discovered, but there was no bow that shot it,” Kim added.

Please direct questions or comments to [englishhani@hani.co.kr]