Indonesia submarine
An KRI Nanggala-402 submarine owned by Indonesia, the same model as the one that went missing on Wednesday.
Alex Widojo/Anadolu Agency/Getty Images
  • The KRI Nanggala 402 went missing near Bali on Wednesday morning with 53 people onboard.
  • Indonesia's navy said Thursday the ship may have sunk 700 meters below sea level.
  • Experts said most rescue crews can't operate past 600 meters.
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The missing Indonesian submarine may be too deep to rescue successfully, the country's navy has said.

The navy has been searching for the KRI Nanggala 402 in waters north of the island of Bali since it missed a scheduled check-in on Wednesday morning. Fifty-three people were onboard.

Indonesia's navy now believes the submarine could have sunk to a depth of 700 meters (2,297 feet), the Associated Press reported.

Navy spokesman Julius Widjojono told a local TV network that the submarine can survive at a depth of between 250 and 500 meters (820 to 1,640 feet), but that the vessel's hull would be in danger of collapsing.

"Anything more than that can be pretty fatal, dangerous," he said, according to Reuters.

Speaking to Agence France-Presse, the French navy vice admiral Antoine Beaussant said of the submarine: "If it went down to rest at 700 meters the likelihood is it would have broken up."

indonesian submarine
The KRI Nanggala-402 submarine.
M Risyal Hidayat/Antara Foto via Reuters

Furthermore, rescue crews can't operate properly below a depth of 600 meters, experts said.

"Most rescue systems are really only rated to about 600 meters," Frank Owen, secretary of the Submarine Institute of Australia, told the AP.

"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."

The cause of the disappearance is not yet clear, but the navy said Wednesday that a power failure may have occurred.

"It is possible that during static diving, a blackout occurred so control was lost and emergency procedures cannot be carried out and the ship fell to a depth of 600 to 700 meters," the navy said in a statement published by Reuters.

indonesia submarine rescue
Indonesian navy ships arrive at the naval base in Banyuwangi on April 22, 2021, to join in the search for the submarine.
(AFP via Getty Images)

The navy added that during rescue attempts, it had discovered an oil spill on the surface of the ocean, which could mean the submarine's fuel tank was damaged.

In an update Thursday, the navy said it had not found any other sign of the submarine, according to Reuters.

Authorities added that the crew onboard had enough oxygen to sustain them until 3 a.m. local time Saturday.

The KRI Nanggala 402 is old by naval standards. The 1,300 tonne vessel was made by Germany in the late 1970s and a two-year refurbishment was completed in 2012 in South Korea, the BBC said.

The Indonesian navy told the BBC it was the first time one of its submarines had gone missing.

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