The investigation results in the sinking of the Navy corvette Cheonan were announced last Thursday, but questions and misunderstandings about the evidence presented by the international investigators remain.
◆ The Torpedo Serial Number
Former unification minister Chung Se-hyun told reporters that the serial number combined with the Korean letter "1 beon" (No. 1), handwritten on the rear of the propulsion shaft of the torpedo that probably sank the Cheonan, is not how the North numbers items since it dates back to Japanese colonial times. Chung said even North Korea's Paekhwawon state guesthouse uses a different numbering system, and the word "ho" is much more common.
But North Korean defectors deny this, saying the numbering found on the North Korean torpedo is the most commonly used form in the North. North Korea Intellectuals Solidarity, a defectors organization, said "beon" is the most common sequential word used in North Korea, while "ho" is used to distinguish between different types of objects, depending on purpose and use. That means the same parts of a missile produced in a factory would be sequentially numbered "1 beon" and "2 beon," according to the group.
◆ How Did the Propulsion Shaft Survive the Blast?
Skeptics continue to argue that a blast powerful enough to split the 1,300-ton Cheonan in half could not have left the propulsion device of a 1.2 m torpedo intact. But experts say the typical characteristics of torpedoes and their blasts make this very likely.
The CHT-02D torpedo that attacked the Cheonan is composed of a high-explosive charge in its nozzle, followed by a propulsion battery, a motor and a propeller at the rear. Out of the entire torpedo measuring 7.35 m in length, the warhead is only 70 cm to 80 cm long. Even if it explodes, the propulsion battery that sits between the warhead and the propeller acts as a buffer, experts say. Also, the propulsion system is made of light and sturdy materials that are not easily destroyed, and more often ends up sinking to the bottom of the ocean largely intact.
That is why the investigation team used fishing nets to find the debris. In 2004, the Agency for Defense Development test-fired a locally made torpedo and retrieved portions of the propulsion system. "The fact that the bulk of the blast heads toward the front rather than the back raises the chances that the propulsion system remains intact," said one expert at a South Korean state-run institute.
◆ Can Mini Subs Fire Mid-sized Torpedoes?
Some skeptics have also said that the 130-ton "Yono" class submarine fingered by the investigators is incapable of firing a mid-sized torpedo. The CHT-02D torpedo that was used to attack the Cheonan is a mid-sized torpedo measuring 533 mm in diameter.
But military experts disagree. Iran's "Ghadir" class subs, which are similar in size to the "Yono" subs carry two torpedo launchers capable of firing 533 mm projectiles. Intelligence officials believe these are actually North Korean "Yono" subs that the North exported to Iran.
In World War II, Japan used 47-ton submarines, which are much smaller than the "Yono" subs, to launch 450 mm torpedoes. Also, North Korea's "Yugo" class subs, which are smaller than the "Yonos," are capable of firing 406 mm torpedoes. "Maintaining balance is important when it comes to firing torpedoes from subs, and a small sub may lose balance when only one of its torpedoes is launched," said one torpedo expert. "But that problem can be solved quite easily."