There are few bonds stronger than that of sailors on a submarine. Each person selected for the crew must fulfill a critical role in an intricate interplay that allows a small metal vessel to dive deep in the sea for weeks at a time.
Corridors are so cramped that sailors cannot pass each other without one person giving way. The whir of the engine thrums, a constant reverberation felt in the teeth. Sailors are stacked in narrow bunks. They practice what one submariner calls “thrifty” breathing, in order to conserve the most precious commodity in a bubble that is cruising underwater: breathable air.
“It’s a very strong brotherhood,” said Frans Wuwung, a retired sailor who trained the crew of the KRI Nanggala-402, one of the Indonesian Navy’s five submarines. “We are friends for life.”
On Wednesday, well before dawn, 53 people descended underwater as the Nanggala began torpedo drills in the southern Pacific Ocean. It should have been a routine activity for the 44-year-old German-made submarine.
The commander of Indonesia’s five vessel submarine fleet, Col. Harry Setyawan, who had started his sailing career on the Nanggala after graduating at the top of his class from the naval academy, was aboard.
About 3 a.m., the Nanggala was granted permission to begin the drill, in waters north of the Indonesian island of Bali. Its dark hull sank into the dark waters. Then silence. Sonar pings went unanswered. The Nanggala had disappeared.
The list of submarine disasters outside of war is thankfully brief. But the drama of underwater struggles, as sailors desperately preserve oxygen while battling influxes of water or internal failures and explosions, is intense. And there are rare miracles. In the case of a Russian Navy submarine trapped in a fishing net in 2005, seven sailors were freed by a rescue crew just a few hours before their oxygen would have run out.
With Indonesian Navy officials counting the dwindling hours of breathable air aboard the Nanggala, ships and aircraft from multiple countries, including the United States, converged on the Bali Sea in hopes of locating the submarine. The fear was that the vessel might run out of oxygen as early as Saturday morning.
Then on Saturday afternoon, Adm. Yudo Margono, the Indonesian Navy’s chief of staff, announced that debris found a couple miles from where the submarine had descended three days before, confirmed that the vessel had sunk to a deep seabed and fractured.
Some of the items found floating in the water had been disgorged from inside the Nanggala: pieces of Muslims prayer mats, special sponges for clearing condensation, and bottles of grease used to lubricate periscopes.
No bodies of crew members have been found, Admiral Yudo said.
Multibeam sonar technology indicated that the Nanggala had sunk 850 meters, Admiral Yudo said, far below what is called “crush depth,” where the pressure is so intense that a steel-hulled submarine could split.
Even if the Nanggala somehow landed in an underwater valley with one of its chambers unbreached by water, the chances of surviving at such depths for so long with limited oxygen is minuscule, said Susaningtyas Nefo Handayani Kertopati, an Indonesian military and intelligence analyst.
“They would be in a panic. What to do?” she asked. “Even if we are locked in a room, we get panicked. Imagine, this is at 850 meters. We are human.”
Mr. Wuwung, the former Nanggala trainer, also said the physics was uncompromising. “It’s very heartbreaking,” he said. “I am devastated.”
What caused the diesel electric-powered submarine to plummet to such depths, below where giant octopi and oarfish tend to roam, is unclear. But naval experts said that the descent was likely rapid and sudden, given that the vessel gave no emergency signals that it was in distress.
“The Indonesian boat most likely went down through an internal problem, through flooding through a pipe that gives way or a battery explosion,” said Norman Polmar, an American submarine historian.
Shortly before it disappeared, the Nanggala was part of another torpedo exercise. But that drill ended “imperfectly,” with the torpedo missing its target, said First Adm. Julius Widjojono, a spokesman for the Indonesian Navy.
The Indonesian Navy chief ordered the submarine to run through the exercise again, which was what the vessel was preparing to do when it went missing, Admiral Widjojono said.
Ms. Susaningtyas raised questions about whether the speed with which the submarine was redeployed allowed enough time for maintenance.
“It was forced into this activity in Bali, very forced,” she said. “The navy chief must take responsibility.”
Built in 1977, the Nanggala was completely refitted in South Korea in 2012. The Indonesian Navy said that the submarine’s paperwork was in order. But a defense expert, who spoke on condition of anonymity to discuss internal navy information, said that the submarine had not undergone a full maintenance since May 2018.
A country of about 17,000 islands flung across the Equator, Indonesia is the world’s largest archipelagic nation. But its naval power does not match its large maritime footprint, and maintenance problems have afflicted its weaponry.
Indonesian naval experts have raised the possibility that as the Nanggala descended on Wednesday, water somehow flooded the submarine, possibly through a pipe or torpedo tube. In perfect conditions, the crew might have had a way to shore the leak and seal off the compartment with watertight doors, but situations rarely unfold perfectly. With the water gushing in, the pressure could send the submarine plummeting.
“The sub would sink very fast, like a stone,” said Soleman B. Ponoto, a military analyst.
The day he left home in Surabaya, the bustling Indonesian city that is home base for the Nanggala, Sgt. Guntur Ari Prasetyo, a diesel technician, asked his wife to pray for him, just as he did each time he was deployed.
Berda Asmara, his wife, complied, but this time, she said, something was off.
“Maybe he had a hunch before he departed,” she said on Saturday. “He looked different this time.”
Ms. Berda, an early education lecturer at a university in Surabaya, said that the wives of the Nanggala sailors are close, sharing WhatsApp groups and meals when their husbands are away. The camaraderie was something that she understood, having grown up as the daughter of a naval officer, she said.
An hour’s drive away, in the city of Sidoarjo, the family of Colonel Harry, the commander of the Indonesian submarine fleet, kept its own vigil on Saturday. His 18-year-old son, Sheeva Naufal Zidane, said he wanted to become a submariner, too.
“Ever since I was a kid, I wanted to be on a submarine, because my father is cool,” he said.
When the television blasted on Saturday afternoon, with news that the submarine debris had been found, Colonel Harry’s family huddled together. As his mother wept, Mr. Sheeva rubbed eucalyptus oil on her feet. The air resounded with prayers.
Winny Widayanti, Colonel Harry’s wife, said that her husband never lost his professional cool, and was calm even during the most heated traffic jams. The debris found in the Bali Sea haunted her, she said, but it would not kill her faith.
“There is still hope, I won’t stop hoping,” she said. “The men will survive. It hasn’t ended yet.”
Hannah Beech and Muktita Suhartono reported from Bangkok, and Dera Menra Sijabat reported from Surabaya, Indonesia. James Glanz contributed reporting from New York.