In a statement published Wednesday night, the Indonesian Ministry of Defense said the KRI Nanggala-402, a German-made submarine, lost contact during an exercise in the Bali Strait — a stretch of water between the islands of Java and Bali that connects to the Indian Ocean and the Bali Sea.
The submarine asked for permission to dive, or submerge, at 3 a.m. local time (3 p.m. ET) before losing contact, it said. The statement added that an oil spill was seen in aerial surveillance near the dive point, around 7 a.m. local time.
Earlier on Wednesday, military chief Hadi Tjahjanto told Reuters that they were “searching in the waters of Bali, 60 miles (96 km) from Bali, (for) 53 people.”
Singapore and Australia have offered to provide assistance.
The 1,395-ton KRI Nanggala-402 was built in 1977 by the German shipbuilding company Howaldtswerke-Deutsche Werft (HDW) and joined the ranks of the Indonesian Navy in 1981, according to the ministry of defense statement.
The submarine underwent a two-year refit in South Korea that was completed in 2012, according to the Indonesian cabinet secretariat’s website.
Indonesia in the past operated a fleet of 12 submarines purchased from the Soviet Union to patrol the waters of its sprawling archipelago.
But now it has a fleet of only five including two German-built Type 209 submarines and three newer South Korean vessels.
Indonesia has been seeking to upgrade its defense capabilities, but some of its equipment still in service is old and there have been deadly accidents involving in particular ageing military transport planes in recent years.