BANYUWANGI, Indonesia—Indonesia’s navy on Saturday declared its missing submarine had sunk and cracked open, killing 53 crew members aboard, after finding items from the vessel over the past two days. Military chief Hadi Tjahjanto said the presence of an oil slick as well as debris near the site where the submarine’s last dive on Wednesday off the island of Bali were clear proof the KRI Nanggala 402 sank. Indonesia earlier considered the vessel to be only missing. Navy Chief Yudo Margono told a press conference in Bali, “If it’s an explosion, it will be in pieces. The cracks happened gradually in some parts when it went down from 300 meters to 400 meters to 500 meters … If there was an explosion, it would be heard by the sonar.” The navy previously said it believes the submarine sank to a depth of 600-700 meters (2,000-2,300 feet), much deeper than its …