Investigators have begun putting together pictures of the doomed Indonesian submarine’s wreckage to discover how the tragedy occurred. After a five-day search, wreckage from Indonesia’s missing submarine KRI Nanggala has been found at a depth of more than 800 meters in the Bali Sea. With no survivors from the 53-person crew — and no certainty the cause of disaster will ever be confirmed — the Indonesian navy will need to decide how much effort it devotes to examining and salvaging the wreckage.
Initial examination of the sunken vessel suggests the wreckage is in three pieces, with the boat’s hull and stern separated. The Indonesian Navy (TNI-AL) has released video footage, taken by a remotely operated underwater vehicle belonging to the Singaporean navy, which appears to show one of the fins mounted on the boat’s stern. The other pictures may show interior sections, but it’s not immediately entirely clear exactly what part of the boat they are. It took one year to find the Argentinian submarine San Juan after it sank in 2017. Nanggala’s discovery so early in the search suggests the boat was near its last reported position. So whatever went wrong likely did so as the submarine was diving.
At this stage, it is impossible to know what triggered the incident. Causes could include a material or mechanical failure leading to catastrophic flooding of one or more compartments. It does not take much loss of buoyancy for a submarine to lose control of its depth.
There could have been a fire, something particularly feared by submariners in their enclosed environment. Or there could have been human error. Submariners, however, have very carefully developed and extensively drilled standard operating procedures. Material failure is the more likely cause.
Regardless of the trigger, the tragic fate of KRI Nanggala would have been sealed once it passed the depth at which its hull and fittings could not withstand the increasing pressure. There is no hard and fast figure for the exact depth at which this occurs.
Submarines such as Nanggala have an individual safe operating depth of at least 260m. What is known as the “crush depth” will be much more than that. But the risk of hull collapse increases very rapidly as depth increases. At 800m, Nanggala had no chance of surviving intact.
Indonesian authorities hope to salvage Nanggala’s wreckage, according to reports. This is possible, and there is some precedent for this. The United States’ 1974 mission codenamed Project “Azorian” involved the covert recovery (from much deeper water) of large components of a sunken Soviet missile-carrying submarine.
Nevertheless, bringing some 1300 tonnes of metal back to the surface from a depth of more than 800m remains a formidable proposition. Only a handful of salvage organisations would even be capable of such a task. It would also be very expensive. One could argue the resource-constrained Indonesian navy has better things to spend its money on, including its remaining four submarines.
Furthermore, there is no guarantee the specific cause of the disaster will ever be discovered. Submarines are large and complex machines, and the “black box” systems in aviation would not cover all the possible problems that might have arisen with Nanggala. The best approach would be to follow up the initial video examination of the wreckage with a more detailed mapping of the wreck site and all the material strewn on the seabed. Coupled with the selective recovery of components, this could help provide some answers.