MELBOURNE, Australia – An Indonesian submarine with 53 personnel on board has gone missing in deep waters during a training exercise, with a submarine rescue vessel from Singapore already on its way to assist in the search.

The German-built Type 209 diesel-electric submarine KRI Nanggala was declared missing in the early hours of Wednesday morning local time in waters north of the Indonesian resort island of Bali after it failed to report the results of a torpedo drill it was undertaking at the time, according to an Indonesian navy spokesman quoted by Reuters.

Indonesia’s military chief, Air Chief Marshal Hadi Tjahjanto, added that neighboring Singapore and Australia had been asked to provide assistance in locating the missing submarine, with ship tracking software showing the former’s submarine rescue vessel MV Swift Rescue already sailing southwards towards Bali as of Wednesday afternoon local time.

The southeast Asian island nation signed a submarine rescue agreement with Indonesia in 2012 and has similar agreements with several other navies, including the United States, to render submarine rescue assistance in the region should a need for such services arise.

The MV Swift Rescue, which is operated by the Singaporean navy but manned by civilian contractors, is equipped with a Deep Search and Rescue Six (DSAR 6) submersible, which is based on James Fisher Defence’s DSAR 500 Class submarine rescue vehicle.

The Swift Rescue will join other Indonesian navy ships already searching for the submarine, with ship tracking websites showing at least two Indonesian corvettes already at the vessel’s last known location, which is reportedly between 700 to 800 meters (2,300 to 2,625 feet) deep.

The KRI Nanggala was built in 1978 and is the Indonesian navy’s second-oldest submarine in its fleet of five boats, having been delivered in the early 1980s and given a comprehensive refit in South Korea in 2012.

Australia has not announced if its own submarine rescue capabilities are being sent for the search. The Royal Australian Navy has a British-designed LR5 which is also managed by James Fisher Defence as its contracted Submarine Escape and Rescue System.