Authorities said ships equipped with specialized tracking equipment had been dispatched within the hope it was the KRI Nanggala 402, which was carrying enough oxygen to last until Saturday morning.
The search zone covers an area of roughly 34 square kilometers.
“We only have time until tomorrow at 3 a.m.” [Saturday] “That is why we are making every effort today,” Indonesian military spokesman Achmad Riad said earlier.
However, as of Thursday afternoon it was still unclear whether the item was the missing ship.
“A strong magnetic field has been detected there,” Riad said, but added that “we have not yet determined its exact location.”
Berda Asmara was amongst those eagerly awaiting news. Her husband, sailor Guntur Ari Prasetyo, 39, was expected to return home from a submarine training mission on the weekend.
“Our last communication was on Monday when he went to work,” said the mother of 1 in Surabaya, a port city on Java. “He said, ‘Pray for me so I can come home soon’ … He told our daughter to listen to me and study hard.”
An oil leak spotted where the submarine likely went down indicated a possible fuel tank failure, raising fears of a deadly disaster.
There were also fears the submarine could have sunk to depths of as much as 700 metres – well below the strength for which it was designed.
The German-built ship was conducting torpedo practice when it requested permission to dive. Contact was lost shortly thereafter.
On Thursday, the U.S. military announced it had sent airborne teams to assist, and one in all two Australian ships sent to the region arrived on the search site.
India and neighboring countries Singapore and Malaysia have already sent ships which can be scheduled to reach this weekend. Among them is the MV Swift Rescue, a submarine rescue vessel.
Indonesia can be counting on a pair of its own submarines — amongst five in its fleet — to assist in the hunt. But hopes of finding the crew alive were fading fast.
“If there is significant damage to the ship itself, that could potentially mean a few things, such as very little space for the crew with very limited oxygen,” said Collin Koh, a naval specialist and researcher on the S. Rajaratnam School of International Studies in Singapore.
“This could also mean that the oxygen reserve tanks could potentially be damaged. This would lower the oxygen levels even further.”
Submarines are equipped with devices to stop carbon dioxide build-up, but when this equipment becomes damaged, it could also pose a serious threat, Koh added.
“It’s not nearly whether there might be enough oxygen, but in addition in regards to the level of carbon dioxide contained in the ship, which could determine the fate of the crew,” he said.
Although Indonesia has never experienced a significant underwater disaster before, such accidents have happened in other countries previously.
One of the worst disasters was the sinking of the Kursk, the pride of the Russian Northern Fleet, in 2000.
The submarine was on maneuvers within the Barents Sea when it sank, killing all 118 people on board. The investigation showed that a torpedo exploded, detonating all of the others.
Most of the crew died immediately, but some survived for several more days – some keeping moving diaries written in blood, addressed to family members – before they suffocated.
In 2003, an accident on a Ming-class submarine during an exercise resulted within the death (almost certainly from suffocation) of 70 Chinese naval officers and crew members.
Five years later, 20 people died from poison gas poisoning when the hearth extinguishing system aboard a Russian submarine being tested within the Sea of Japan by accident activated.
In 2018, authorities found the wreck of an Argentine submarine that had disappeared a 12 months earlier with 44 sailors on board.
