Military divers plunged into the waters near South Korea's tense maritime border with North Korea to search for 46 missing marines from a naval ship that sank Saturday, but were hampered by fierce waves and high winds, officials said. Hopes were fading for the missing crew after an explosion sank the ship in one of South Korea's worst naval disasters. Divers tried unsuccessfully twice to get to the wreckage, Rear Adm. Lee Ki-sik of the Joint Chiefs of Staff told lawmakers. There was speculation the ship may have hit a wayward mine. The explosion at the rear of the Cheonan shut down its engine, wiped out power and caused the ship to sink a little over three hours later, the Joint Chiefs of Staff said. A survivor, Staff Sgt. Shin Eun-chong, 24, told relatives he was on night duty when he heard a huge boom behind him that split the ship apart. The vessel started tilting, and his glasses fell off his face as he hit the deck, relatives at a naval base in Pyeongtaek told The Associated Press. Military planes and boats were searching the waters near South Korea's Baengnyeong Island where the 1,200-ton Cheonan had been on a routine patrol mission. Among the missing was a marine who had survived a 2002 naval skirmish with North Korea, South Korea's Yonhap news agency said.