While too soon to state definitively that the submarine has been lost with all 53 crew, the chances of survival are extremely small. This is because of a number of factors: the age of the submarine; the deep water in which it was operating; the absence of any signs such as distress flares – and finally reports that a lot of surface oil has been seen in the area. To take these separately:
- KRI Nanggala (402) was commissioned in 1981, having been ordered four years earlier from the German shipbuilder HDW. Based on the popular Type 209 design, Indonesia operated two of them, known domestically as the Cakra class. They were the only two submarines operated by the Indonesian navy until the first of the new Nagapasa class was commissioned in 2017.
Type 209s are a sound, if now dated design. A total of 61 were built – though entirely for the export market with Germany preferring to remain for several decades with small Type 206 submarines until the very modern Type 212 that started to enter service from 2005.
The life of a submarine, generally speaking, is measured in the number of deep dives it can perform. The more of these that occur, the greater the stress on the hull – and there is a very firm limit on how many can be performed before the submarine is no longer safe and has to be retired. Nanggala underwent a major overhaul in South Korea between 2010 and 2012. Depending on the nature of the work, that might have extended the life of the pressure hull – but the laws of metallurgy and physics are such that it cannot be prolonged forever.
Without knowing the operational dive profile of the submarine – and waters in the Indonesian archipelago tend to be quite shallow – it is impossible to be precise about how close the submarine was to being decommissioned. However, it must have been getting near to its limit. Put simply, the older a submarine is the more likely it is to have a weaker pressure hull as it has been compressed and expanded many times, first diving deep and then returning to near, or on, the surface.
- Reports indicate that Nanggala was operating in waters north of Bali with a depth of 600 metres and more. The diving depth of a submarine is highly classified for operational reasons, but if we go by the general performance characteristics of the Type 209 family, these could reasonably be expected to have a maximum diving depth of 300 metres. All submarines are over engineered for safety and for that reason it might be possible that survival down to 400 metres is possible – but not at 600, which would seem to be well past the crush depth of the hull.
- A damaged submarine in deep water has limited options to communicate. Radio signals do not pass through water at great depth, except for very low and ultra low frequency signals and it is unlikely that the Nanggala carried such equipment. However, all submarines carry numerous emergency flares that can be launched from a small tube in the pressure hull. Typically, these float to the surface and when there, burn extremely brightly and give off a lot of smoke to attract as much attention as possible. There are no reports of any flares being sighted.
- Apparently, an oil slick has been spotted on the sea surface in the area where the submarine has gone missing – and this is extremely bad news because if it has come from Nanggala it indicates that there has been a catastrophic failure in the hull. The forces needed to rupture a diesel tank are extreme and indicate that the submarine has suffered extensive damage. Having said that, oil slicks are a relatively common sight – but in this case the proximity to the last known position of Nanggala and the timing of its appearance is unlikely to be coincidental.
The search is now underway for the submarine and when it is eventually discovered – and it will be, probably by a towed variable depth sonar – it might then be possible to find evidence of how the accident occurred. Tragically, the chances of any of the crew surviving are infinitesimally small.
UPDATE: Indonesia has accepted Australia’s offer to assist in the search for missing submarine, KRI Nanggala (402). HMA Ships Ballarat and Sirius, both presently at sea on separate regional deployments, are making best speed for the search area. The Anzac Class frigate Ballarat, equipped with sonar capabilities and an embarked MH-60R helicopter, is expected to be in the search area today after transiting the Lombok Strait. The support ship Sirius is off the coast of Brunei and will be in the search area from around Tuesday. Sirius can replenish ships with fuel, water and stores by day and night.
Commander of Joint Task Force 635, Rear Admiral Mark Hammond, said the Australian Defence Force stands with its neighbour at this distressing time. “My thoughts are with the submariners of KRI Nanggala, their families and the Indonesian people. As always, we stand ready to assist our fellow mariners in the Indonesian Navy. These two Australian ships will help expand the search area and extend the duration of search effort.”