A very difficult Cheonan investigation was revolutionized by dredging vessels using high tensile nets to scour the sea floor for evidence, it was revealed in the Q&A session following today’s release of the results of the investigation by a joint civil-military investigation team.
Frustrated by currents and water depth, the investigation team discovered that the Republic of Korea Air Force had employed dredgers in the past to “collect most of the evidence fragments” from lost jets in waters up to 372m deep in the East Sea, and 45m deep off the west coast.
Thereafter, on April 1st and using special, high tensile nets, the team began dredging the area, using the nets as many as eight times each day until the morning of May 15th when the evidence which forms the basis of the case against North Korea was found.
Told that the important parts would probably lie around 30 to 40m from the original detonation site, the team created a grid of 500 yards by 500 yards, and within it 25 yards by 25 yards, all across the area as the basis of the search. In the end, the section of a North Korean torpedo was recovered from an area “slightly above the original detonation point” which had been searched “several dozens of times” before.
“Divine luck,” explained Kim Nam Shik, the captain of the dredger, “allowed us to finally salvage this evidence.”
Ultimately, Lieutenant-General Kang Won Dong, the director of the multinational support element of the joint-investigation team explained that the team was able to conclude that a Yeonho Class midget submarine had infiltrated South Korean waters via the fringes of international waters to avoid detection on the night of March 26th, before approaching the Cheonan, identifying it as a South Korean naval vessel, and torpedoing it with a “CHT-02D” torpedo.
The team noted intelligence that one Sangeo Class (300 tons) and one Yeoneo Class (130 tons) vessel had left port on North Korea’s west coast before the attack, returning some time afterwards. The Yeoneo Class is similar to the older Sangeo Class of North Korean submarines, and both are classified as midget submarines by being less than 300 tons in weight.
In order to prove that the torpedo was responsible for sinking the ship, the team tested samples of “large amounts of white powder” found on the ship’s hull and the propeller of the torpedo, alongside substances produced by a test explosion of 15g of explosive in 4.5 tons of sea water.
The results of the tests showed that the substance found on the hull of the vessel and the torpedo was aluminum oxide, with additional evidence of graphite. Both are substances made by rapid cooling of a high temperature environment. According to the explanation of the team, 20 to 30kg of aluminum is added to most modern torpedoes, to enhance explosion size and help create bubbles.
Areas of damage to the hull, they explained, were due to this “rapidly oxidizing aluminum powder.”
The team was finally able to conclude that the torpedo exploded outside the Cheonan, some 69m below portside, but that the ship was destroyed by a pillar of bubbles and water created by that explosion.
The evidence for this presumption was the testimony of a sentry stationed on Baekryeong Island at the time of the explosion who said he saw a one hundred meter high “white flash” in the ocean, that of the port lookout on the Cheonan who said he felt droplets on his face at the time of the explosion, survivors who testified to “indentations so deep on port side that their ankles would disappear into the holes”, and the samples of explosive materials found all across the ship.
The team added that footage from CCTV cameras on the ship had been retrieved, and showed a ship operating normally until one minute before the explosion. However, they declined to release the footage publicly out of respect for the families of the deceased.
