Government and military officials have reportedly ruled out that an accident or collision with a reef caused the 1,200 ton Navy corvette Cheonan to sink in waters 1.8 km southwest of Baeknyeong Island near the de facto sea border with North Korea on Friday. They say the explosion that sank the ship was strong enough to rip it in half.
But experts are divided over whether the blast could have been caused by a torpedo, floating mine or other external shock or an internal accident such as an explosion of ammunition or fuel stored in the vessel.
"The tragedy may have been caused by a floating mine, judging by the explosion in the rear of the ship as well as the situation inside the vessel before it sank and geographic conditions," a government official said. "But we cannot guess the possible cause until we are able to investigate the vessel."
◆ External Shock
"That type of destruction could not have been caused by an internal explosion," said Yoon Yeon, a former commander of Naval Operations. "It was probably a floating mine or a torpedo. Patrol boats store munitions with the fuses and explosive materials in separate areas of the ship so accidental explosions rarely occur, and those storage facilities have double or triple locks so that it is difficult for most people to access them."
Kim Tae-wook, a managing director at Hyundai Heavy Industries said, "It appears that the shock from an explosion from the outside triggered the munitions stored inside the vessel to go off, causing the ship to split in half."
Experts who point to an external shock say the most probable cause was a floating mine. The Cheonan was built according to U.S. specifications and is said to be able to remain buoyant even if 15 to 17 percent of the ship's hull is damaged. They also say that it is difficult for a single torpedo to split a vessel of that size in half and cause it to sink.
An explosive expert said, "Ships are stronger than we can imagine, so it is almost impossible for them to break in two due to an internal explosion." He notes the fact that some survivors said they did not smell any explosives, which means the ship could have been destroyed in a non-contact explosion underwater.
◆ Internal Explosion
"If a single torpedo or a floating mine caused a naval patrol vessel to split in half and sink, we will have to rewrite our military doctrine," said Baek Seung-joo of the Korea Institute for Defense Analyses. Instead, he believes an accident within the vessel is to blame.
It is unlikely that a single torpedo or a floating mine will accurately hit the munitions or fuel storage areas of a ship. A staffer at a security-related research center said, "With the exception of the naval clashes with North Korea in the West Sea, most South Korean naval accidents were due to internal explosions. One military expert, who spoke on condition of anonymity, cautiously raised the possibility of an "internal act of terror."
◆ Cautious Approach
Former Navy Chief of Staff Adm. Song Young-moo, said, "Some people are pointing the finger at North Korea, but anyone with knowledge about the waters where the shipwreck occurred would not draw that conclusion so easily." Experts say those waters are only 25 m deep and characterized by rapid currents, making it very difficult for North Korean submarines or semi-submersible vessels to operate.
"An accurate assessment will be possible only after observing the hull and debris from the blast," Song said. "Until then, it is very dangerous to raise the possibility of a North Korean attack."