As reported in various outlets, the Indonesian government has lost all contact with the KRI Nanggala-402 submarine. The military lost contact with the submarine about 53 miles north of the island of Bali in the Pacific. The Nanggala was in a training area to practice a live torpedo firing drill. It was executing a dive from the surface at 0300hrs local time Wednesday when all contact with it was lost. The boat missed a scheduled check-in call sometime after 0430 hrs.

The Nanggala and a sistership were built in Germany as the Cakra Class in the 1970s and delivered to Indonesia in 1981. They have a diesel-electric propulsion system and displace about 1,500 tons submerged. Both boats have seen extensive refits and modernizations over their long life span. South Korea completed the Nanggala’s most recent refit in 2012. The refit replaced her conning tower, weapons, sensor systems and updated her engines and batteries. Her dive depth was increased slightly to 843 feet and her speed to 25 knots on the surface.

According to Indonesian government sources, the submarine had 53 crew aboard.

Partners Assist in Search for Indonesian Submarine

In a Reuters story, Indonesia military chief Hadi Tjahjanto stated that search and rescue efforts were ongoing in the area of the submarine’s last reported position. Indonesia has requested the assistance of Singapore and Australia in the effort. Singapore will likely provide the civilian-crewed MV Swift Rescue. The vessel equipped with a Deep Search and Rescue Six (DSAR 6). The Australian Navy uses a James Fisher Defence-owned and U.K.-designed LR5 for submarine rescues.

Indonesia is a signatory to several submarine rescue agreements between itself, Singapore, Australia, and the U.S. The report of the missing submarine would be forwarded to the International Submarine Escape and Rescue Liaison Office, a part of NATO.

At 0700hr local time, an Indonesian rescue helicopter reported the presence of a fuel oil slick in the area of the submarine’s last-known position. The aircraft sighted no other debris. The oil slick could indicate a ruptured fuel tank aboard the submarine. But it could also be an intentional release of fuel oil by the crew to mark its position for rescuers.

According to reporting by U.S. Naval Institute News, Indonesia is rushing ships to the area to augment the corvettes KRI Bung Tomo (357) and KRI Kapitan Pattimura (371) in the search efforts. These additional vessels include the survey ship KRI Rigel (933) and the minehunter KRI Pulau Rengat (711).

Nevertheless, the sea depth in the area of the Nanggala’s last dive is over 2,100 ft. This is more than double the Nanggala’s maximum rated depth.