Investigators say a North Korean midget submarine and a support vessel left a naval base on the west coast two to three days before the attack on the South Korean corvette Cheonan on March 26 and returned to port two or three days later.
They said the submarine and support vessel left the base on Cape Bipagot, around 80 km from Baeknyeong Island on March 23 and maneuvered out of the sight of South Korean and U.S. intelligence. The ship apparently accompanied the submarine to provide support and offer aid in case the sub encountered difficulties. The submarine took a detour out into open seas and arrived in waters to the west of Baeknyeong Island on March 25. There it is believed to have awaited its prey 10 m under the surface for about a day.
The military believes that the submarine found the Cheonan on the evening of March 26 and fired a CHT-02D torpedo at the vessel from 3 km away. At the time of the attack, the Cheonan was in waters that are 30 to 40 m deep, while the North Korean submarine was further out at sea where the water is between 40 to 50 m deep, posing no problems to launching a torpedo.
"When the sub attacked the Cheonan at 9:22 p.m. on March 26, the tides in the West Sea were slow, and it looks like the North strategically planned the attack," said a military source. The sub apparently returned to Cape Bipagot on March 28.
The submarine class was unknown until now. The 130-ton sub ranks between the shark (325 tons) and a Yugo class (85 tons). Air Force Lt. Gen. Hwang Won-dong, the chief of the intelligence analysis team, said, the sub "is similar to the shark-class submarine and was built recently for export, equipped with night-vision equipment and other high-tech gadgets, as well as a unique structure to enhance its stealth capabilities." Intelligence experts say the sub is the same as the three "Ghadir" class midget submarines the North exported to Iran.
At first, investigators suspected a shark-class sub of the attack because they were unaware of the movements of this class, dubbed "Yono" or salmon. But by backtracking information, they apparently discovered the new class. "Two North Korean subs left the naval base two or three days before the attack, but we were unable to detect this," said Sohn Ki-hwa of the intelligence team said. "This will not lead to major shifts in our intelligence assessment capabilities, but we will improve what needs to be improved."
But questions linger why the Cheonan, a battleship equipped with sonar equipment, was unable to detect the movements of the sub or the launch of the torpedo. "The Cheonan's sonar is an old model with a limited range, so there's a strong possibility that it failed to detect the torpedo which was launched from far away," said a military source.
Experts say North Korean subs and other ships probably conducted several infiltration and surveillance operations in waters near Baeknyeong Island. "We have no information whether North Korea conducted prior surveillance of the waters where the attack was carried out, but we believe it carried out training missions in waters off North Korea's coast with similar underwater conditions," Hwang said.