KIEL, Germany – A leaky seal in a submarine’s trash disposal unit can result in water flooding in as the vessel dives. This eventually corrodes the battery cable housing, which causes the battery to glow, spark and then explode.

This nightmare scenario of a submarine flooding and catching fire from the inside out while still underwater is not hypothetical, but was what led to the death of three US crew members on board the USS Bonefish on April 24, 1988.

Ahead of taking command of the Republic of Singapore Navy’s (RSN) four new Invincible-class submarines – the last of which, the Inimitable, was launched in Kiel, Germany, on April 22 – Singapore’s sailors are undergoing rigorous training to prepare them for all scenarios.

Through simulator work and punishing command courses, the objective is for the crew to train and be drilled until competent handling of the new boats’ systems becomes almost muscle memory, said Lieutenant-Colonel Xander Lim, head of operations and training at the submarine project office.

For instance, a virtual procedural trainer (VPT) replicates about 12 million parts of an Invincible-class submarine in software, and links with other simulators such as a combat trainer, a steering and diving trainer system, and a new maintenance trainer.

The system can be used by multiple trainees to teach them to handle a full spectrum of emergency situations, such as flooding or a fire in the galley. This means an entire set of submarine crew can conduct drills at the same time on the same virtual boat using avatars, like in a multiplayer video game.

LTC Lim said the VPT reduces the time that the submarines are used for training purposes, which means a more optimum maintenance and operations cycle.

Meanwhile, Lieutenant-Colonel Tan You Cai was the sole Singaporean participant in Germany’s submarine commanding officer course that ran from November 2023 to March 2024.

Commonly known as the Perisher course, it has a reputation for being among the finest naval command programmes in the world.

The one run by the Dutch navy, for instance, has a failure rate of over 50 per cent.

LTC Tan, 36, recalled a periscope exercise that tested his decision-making skills under high pressure.

While warships charged towards his submarine, he had to calculate whether he was at risk of being run over by the ships, and the final moment when he had to take evasive action to keep the submarine safe.

“The mission was to keep at periscope depth for as long as possible... They want you to meet your mission while staying safe, and that is where you need to decide the right time to avoid and the right time to come up and attack them,” he said.

LTC Tan, who is the executive officer (designate) of Impeccable, another Invincible-class submarine, said he found himself able to rely on his training to get through the course run by a nation with a long naval history.

Asked if he thought the RSN is on a par with the German navy, he said that in terms of experience, Singapore has a long way to go because the Germans have had combat experience. But in terms of competency, he feels the Republic’s sailors are not far off.

“Attending these courses will help us gain some experience, at least by proxy,” he said.

The course also helped LTC Tan understand himself better as a submariner and a leader managing a crew, to ensure he could execute his mission while maintaining high morale, he added.

Morale is critical for submarine crews, given the long months spent shoulder to shoulder underwater in what is essentially a metal tube.

Military Expert 3 Hariiheran Naidu, 36, said food is a huge morale booster, and the days when the crew gets chicken rice and laksa were the most unforgettable. He has also spent several birthdays underwater, and marked each occasion with a frozen Sara Lee cake.

Naval officers said they welcome quality-of-life improvements on the new submarines, which are the RSN’s first to be fitted with built-in rice cookers. They are also the first crew members to have their own beds instead of having to share bunks, which ME3 Hariiheran is especially pleased about as he now has his own space to put up pictures of his family.

“When you’re really having a bad day, you go back and look at these pictures, it’ll really boost your morale,” he said.

At the Inimitable’s launch on April 22, Senior Minister Teo Chee Hean said Singapore’s new submarines have many advanced capabilities, but a boat is only as good as its crew. He exhorted the new generation of submariners to safeguard Singapore’s peace and security with tenacity and distinction, as their predecessors had done.

“Our submariners will need imagination and daring to translate the new capabilities of our submarines into fresh fighting concepts,” said SM Teo, who is also Coordinating Minister for National Security.

“To the crew of Inimitable, I encourage you to live up to your boat’s name – to be matchless and unrivalled in the execution of your duty.”