The Indonesian Navy recently lost a submarine that sank off the coast of Bali which was found split into three pieces on the seabed, killing all the 53 sailors on board. The submarine KRI Nanggala 402 disappeared after it requested permission to dive during a live torpedo firing drill. The ill-fated Nanggala, like all submarines in peacetime, trains for war as effectively as possible, in the knowledge that this will contribute to its prevention.
The KRI Nanggala 402 was a Cakra class submarine of Type 209/1300 attack submarines developed by Howaldtswerke-Deutsche Werft of Germany that were bought and commissioned by the Indonesian Navy in the 1980s. In 2012, the 44-year-old Nanggala underwent a midlife refit to extend its serviceability for a few more years.
Submarines have pressure hulls, which withstand the hydrostatic pressure at the depth at which the submarine is designed to operate. Each submarine hull is designed to withstand the pressure up to a certain depth beyond which it would simply crush due to the hydrostatic force at that depth. For this reason, every submarine has a diving depth. Generally, the thickness of the hull and the type of material decide the maximum crushing depth of the submarine.
Similarly, in the case of the Indonesian submarine, it was suspected to have a power failure which resulted in the failure of some control system and therefore, may have lost control and sunk beyond its crushing depth. It is highly impractical for a submarine to be designed to withstand a pressure of up to 730 metres of water. This was what would have led to the submarine hull being broken into three pieces as preliminary findings indicate.
The underwater environment is a dangerous one and therefore submarines face many perils of the deep. Even a small fire or gas leak inside a submerged submarine can have catastrophic consequences. A collision with another vessel or grounding may be much more serious.