Admiral Yudo Margono, chief of staff of the Indonesian navy, said the submarine had sufficient oxygen for 72 hours, based on calculations from when the ship lost contact during a military exercise on Wednesday.
The German-made KRI Nanggala-402 asked for permission to dive or immerse at 3 a.m. local time Wednesday before losing contact, authorities said. Margono said the submarine had just fired two torpedoes – one with real ammunition and another with a training head – as part of training exercises in the Balis Strait, a stretch of water between the islands of Java and Bali that connects to the Indian Ocean. and the Bali Sea.
Answering questions about the submarine’s condition before participating in the war simulation, Margono said the KRI Nanggala-402 and its entire crew are well prepared. It last arrived for maintenance in 2020 in Surabaya, a port city on the island of Java, he said.
The military suspects that an oil spill seen in air surveillance near the dive point on Wednesday came from the vessel. Margono said the fleet also found an object at a depth of 50-100 meters (about 164-328 feet) that was magnetic, meaning it probably came from the submarine.
Margono said there are two possibilities to explain the oil spill seen on the surface: the submarine tank may leak because it dives too deep, or the submarine released liquid on board in an attempt to rise to the surface.
Indonesian Navy spokesman First CEO Julius Widjojono said the submarine has the ability to dive up to 500 meters (approximately 1,640 feet) below sea level, but authorities estimate it went 100-200 meters below that depth.
Two ships equipped with a side-scan sonar, a tool used to map the seabed, began searching the area Wednesday, the Department of Defense said, while a Rigel warship equipped with sophisticated sonar that can accurately detect the ship’s position is on its way from Jakarta, according to Widjojono.
Authorities hold out hope that the crew is safe, but acknowledged the situation could be deadly at that depth.
“Let us pray for them so they can survive,” Widjojono told local media on Wednesday.
The International Submarine Escape and Rescue Liaison Office (ISMERLO), an organization that facilitates an international response for distressed submarines, also provides assistance, the Department of Defense said.
The 1,395-ton KRI Nanggala-402 was built in 1977 by the German shipbuilding company Howaldtswerke-Deutsche Werft (HDW) and joined the rank of the Indonesian Navy in 1981, according to a ministry statement.
The submarine underwent a two-year redevelopment in South Korea, which was completed in 2012, according to the Indonesian Cabinet Secretariat.
Previously, Indonesia operated a fleet of 12 submarines purchased from the Soviet Union to patrol the waters of its scattered archipelago. But now it has only a fleet of five, including two German-built Type 209 submarines and three newer South Korean ships.
Indonesia has tried to upgrade its defense capabilities, but some of its equipment still in use is outdated and there have been fatal accidents in recent years, especially with aging military transport aircraft.
CNN’s Kara Fox contributed to this report.