Blaming North Korea, South offers detailed account of how torpedo sank Cheonan
| Seoul, South Korea
The prolonged investigation into the sinking of the South Korean Navy corvette Cheonan does more than blame North Korea for the attack. It provides graphic details on the construction of a torpedo, how a torpedo works, and what happens when a torpedo is fired and hits its target.
In the campaign to generate international support for condemnation of North Korea, South Korea鈥檚 Defense Ministry meticulously summarized critical information in fairly simple language on the basis of conclusions reached by a Joint Civilian Military Investigation Group that included experts from 10 Korean agencies as well as the United States, Australia, Britain, and Sweden.
Here鈥檚 what happened after 鈥渁 strong underwater explosion generated by the detonation of a homing torpedo below and to the left of the gas turbine room鈥� of the Cheonan made it 鈥渟plit apart and sink,鈥� according to the assessment of the Joint Civilian-Military Investigation group.
First, the 鈥渟hockwave and bubble effect caused significant upward bending鈥� of the keel of the vessel, 鈥渁nd the shell plate was steeply bent with some parts of the ship fragmented.鈥�
Then, 鈥渙n the main deck, fracture occurred around the large openings used for maintenance of equipment in the gas turbine room.鈥� The bulkhead of the room 鈥渨as significantly damaged and deformed.鈥�
At the same time, 鈥渢he bottoms of the stern and bow sections鈥� were 鈥渂ent upward鈥� 鈥� further evidence of an underwater explosion.
Examined stern for six weeks
The investigation team, over the course of six weeks of examining the smaller stern section of the ship and the larger main portion, 鈥渇ound evidence of extreme pressure on the fin stabilizer,鈥� needed to reduce rolling of the ship, as well as 鈥渨ater pressure and bubble effects on the bottom of the hull.鈥� The fact that wires were cut 鈥渨ith no traces of heat鈥� added to the impression of 鈥渁 strong shockwave and bubble effect causing the splitting and the sinking of the ship.鈥�
South Korean officials were convinced, after recovery of both portions of the ship, that North Korea was responsible, but the best evidence of a torpedo attack was discovery of the torpedo itself, including the motor with propellers and steering section, last Saturday.
The rusted torpedo, on display in a glass case at the Defense Ministry, was found after weeks of hunting by a commercial dredging ship at a depth of approximately 150 feet. The captain of the dredger said the nets for pulling it up broke a number of times, but 鈥渢he moment it was above water, we thought instinctively, this is what we are looking for.鈥�
Moreover, said a defense official, 鈥渢he explosive substances found in the Cheonan and on the propeller were identical.鈥�
The report offers still more precise information. The torpedo parts include 鈥渂laded contra-rotating propellers, propulsion motor and a steering section鈥� that 鈥減erfectly match the schematics鈥� of a torpedo 鈥渋ncluded in introductory brochures provided to foreign countries by North Korea for export purposes,鈥� said the summary report.
The torpedo 鈥渦tilizes acoustic/wake homing and passive acoustic tracking methods,鈥� said the report. 鈥淚t is a heavyweight torpedo with a diameter of 21 inches, a weight of 1.7 tons and a net explosive weight of up to 250 kilograms.鈥�
It was the sheer force of the blast, not shrapnel or burning, that killed the sailors and broke up the ship, according to analysis attributed in the final report to the Korea Institute of Geoscience and Mineral Resources.
That analysis cited 鈥渟eismic wave intensity of 1.5 degrees鈥� and two infrasound waves with a 1.1 second interval, enough to tear apart the ship. 鈥淭he seismic wave and infrasound waves originated from an identical site of explosion,鈥� said the report. 鈥淭his phenomenon corresponds to a shock wave and bubble effect generated by an underwater explosion.鈥�
The investigators conducted 鈥渘umerous simulations of an underwater explosion鈥� that showed that a detonation with a net explosive weight between 200 and 300 kilograms had occurred at a depth of between approximately 18 and 27 feet, and nine feet left of the center of the ship鈥檚 gas turbine room.
The report categorically ruled out shifting tidal currents, metal fatigue, old mines in the area, collision with another vessel or an explosion inside the ship. These, it said, 鈥減layed no part in the incident.鈥�
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