The Indonesian submarine KRI Nanggala 402, with a crew of 53, disappeared on Wednesday during exercises off the coast of Bali, sparking a frantic search to locate the stricken vessel. Australia, India, Malaysia, Singapore, and the United States have sent specialized ships or aircraft in response to Indonesian requests for assistance.

If the submarine was still intact, officials said it would only have enough air to last until early Saturday morning.

Reuters reports that Indonesia’s navy said it was investigating whether the submarine lost power during a dive and could not carry out emergency procedures as it descended to a depth of 600-700 metres, well beyond its survivable limits.

The 44-year-old diesel-electric powered submarine could withstand a depth of up to 500 metres (1,640 ft) but anything more could be fatal, Navy spokesman Julius Widjojono said. The Bali Sea can reach depths of more than 1,500 metres.

An object with “high magnetic force” had been spotted “floating” at a depth of 50-100 metres, Indonesian Navy Chief of Staff Yudo Margono said, and an aerial search had earlier spotted an oil spill near the submarine’s last location.

Indonesia operates five submarines – two German-built Type 209s including Nanggala and three newer South Korean vessels.

Nanggala-402: The search for a missing submarine

Thanks to David Rye for contributing to this post.