A search is underway for an Indonesian submarine that is thought to have sunk too deep to retrieve.
There are 53 people on board the sub, which was taking part in a training exercise off the coast of Bali when it missed a scheduled reporting call.
Indonesia’s navy ships and rescue ships from neighbouring countries are looking for the vessel, but the navy said it believes it may have sunk to a depth of 600-700 metres - much deeper than its collapse depth which is estimated at 200 metres, according to a firm that refitted the vessel in 2009-2012.
Officials reported an oil slick and the smell of diesel fuel near the starting position of the diesel-powered KRI Nanggala 402’s last dive, about 96 kilometres north of Bali, though there has been no clear evidence that they are linked to the submarine.
Ahn Guk-hyeon, an official at South Korea’s Daewoo Shipbuilding and Marine Engineering, said most submarines collapse if they go deeper than 200 meters because of pressure on the hull.
He said his company upgraded much of the Indonesian submarine’s internal structures and systems but it currently lacks information about the vessel because it hasn't been involved with any work on the ship in the past nine years.
Frank Owen, secretary of the Submarine Institute of Australia, also said the submarine could be at too great a depth for a rescue team to operate.
“Most rescue systems are really only rated to about 600 metres," he said. "They can go deeper than that because they will have a safety margin built into the design, but the pumps and other systems that are associated with that may not have the capacity to operate. So they can survive at that depth, but not necessarily operate.”
Indonesia’s military said that five navy ships and a helicopter were taking part in the search while a hydro-oceanographic survey ship equipped with underwater detection capabilities is on its way to the site around the oil spills.
Rescue ships from Singapore and Malaysia are expected to arrive on Saturday. The military said Australia, the United States, Germany, France, Russia, India and Turkey have also offered assistance.
Singapore's defence minister Ng Eng He confirmed it had dispatched its submarine rescue vessel. “Our fervent prayers and hopes go out to the crew of KRI Nanggala, for their safety and resilience,” he wrote on Facebook.
Indonesia’s navy said an electrical failure may have occurred during the dive, causing the submarine to lose control and become unable to undertake emergency procedures that would have allowed it to resurface.
It was rehearsing for a missile-firing exercise that was to take place on Thursday.
The German-built submarine, which has been in service in Indonesia since 1981, was carrying 49 crew members, its commander and three gunners, the Indonesian defence ministry said.
It had maintenance and overhaul in Germany, Indonesia and most recently in South Korea, from 2007 to 2012.
Indonesia currently has a fleet of five submarines and plans to operate at least eight by 2024.