Indonesian Submarine "Nanggala" LIKELY SUNK, NO HOPE.

On April 21, 2021, the Indonesian Navy reported that its submarine KRI Nanggala (492)  disappeared in waters about 95km north of Bali.^[16] Nanggala had been conducting a torpedo drill, but failed to report its results as expected.^[17] The navy stated that Nanggala had requested permission to dive to perform firing of a SUT torpedo^[18] at 3am Indonesian time.  Around an hour after being given clearance, Nanggala  lost contact with surface personnel.^[20][21] The Indonesian Navy subsequently sent a distress call to the International Submarine Escape and Rescue Liaison Office to report Nanggala missing and presumably sunk.^[22] The Indonesian Navy stated it was possible that Nanggala experienced a power outage before falling to a depth of about 700m.^[20]

No usual radioing-in from Nanggala to Indonesian ships, naval bases or satellites or other distress signals (eg. flares) have been heard or seen. Based on a similar case, that of Argentine submarine ARA San Juan, in 2017, total loss of contact of a sub, usually indicates it has been lost with all hands (ie. no hope for Nanggala's approximately 50 officers and crew). 

KRI Nanggala's approximate last position. (Map courtesy Sydney Morning Herald)
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Around 7am Indonesian time, an aerial search revealed traces of oil spill on the surface of the water near the location where the submarine was believed to have dived.^[25][19] Oil slicks, if from Kri Nanggala, can indicate its diesel fuel tanks have ruptured under extreme crush depth water pressure - which may indicate KRI Nanggala was "lost with all hands" ie. sunk with the whole crew. The seabed is reported to be a submarine crushing 700m deep where Nanggala was lost.

Indonesia has requested assistance from the Singaporean and Australian Navy submarine rescue ships which can deploy deep diving rescue submersibles. Indonesia has an agreement with Singapore for submarine rescue. The Singaporean Navy's MV Swift Rescue has already departed Singapore's Changi naval base and can be seen on this marine satellite tracking site.

Significantly KRI Nanggala is a very old (40 year old) submarine -  a German built TKMS (was HDW) Type 209 conventional diesel-electic submarine. It was commissioned into the Indonesian Navy in 1981 and its last reported major maintenance/overhaul was in South Korea, in  2011. 

A 40 year old submarine, perhaps with decades old torpedoes, can suffer many technical defects.

5 POSSIBLE REASONS KRI NANGGALA MIGHT SINK:

1. seawater leaks through the snorkel when sucking in surface air at shallow depth. In a 2017 (Argentine submarine  ARA San Juan) lost submarine case seawater gushed through the snorkel down to the submarines 100s tonnes of lead-acid Batteries causing a release of poisonous, highly flammable and explosive hydrogen gas, which sank ARA San Juan in 2017. It is possible similar has happened to Indonesia's KRI Nanggala.

2.Human error and/or failure of torpedo tube equipment in a torpedo firing drill, can leave the tube outer or inner door(s) OPEN - thus allowing seawater to rush in. This quickly makes a sub "nose-heavy" with too much weight to be counteracted by Nanggala's usual air-tank buoyancy. This would cause Nanggala to sink to (around 400m deep, "crush depth") thus imploding, totally destroying,  Nanggala.

3.Deploying and/or dropping very old "live torpedoes" during test firing always carries risks that the torpedoes' highly flammable/explosive propellent manages to leak, and any sparks/electrical equipment sets it on fire - leading to smoke/poison gas and ultimately catastrophic explosion. This is what happened to the sunk Russian submarine Kursk in the year 2000.

4. Submarines are normally decommissioned after 30 years. One major reason is too many "cycles" of immersion/contraction of their Pressure Hulls causes Metal Fatigue. This makes a submarine unsafe to dive anywhere below about 100m deep. If Nanggala dived to (say) 250m its pressure hull may have "failed" ie. collapsed inward/imploded instantly destroying Nanggala.

5. The Indonesian Navy said an electrical failure may have occurred during the dive, causing the submarine to lose control and become unable to undertake emergency procedures that would have allowed it to resurface.

FINALLY DETERMINING WHAT HAPPENED

Sidescan sonar and deep sea manned or unmanned submersibles might locate Nanggala, or fragments of it, on the seafloor in the next 24 hours, or longer,

Failing that undersea sensors, belonging to the US Navy, that are nearby eg. 100s kms away  from where KRI Nanggala was lost, will be able to detect any loud sounds, like an imploding submarine hull. Due to secrecy the US will need to claim that it was the loud sound/nuclear test sensors of the international civilian "Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO)"  that picked up Nanggala's last sounds (especially any metal pressure hull cracking implosion). 

A big IF (but it is unlikely) Nanggala is intact and on a shallow seafloor, with most crew alive, Nanggala's use of its loud-booming active sonar could be heard by undersea sensors that are permanently fixed or on surface ships, aircraft or on other submarines. But unfortunately it is unlikely any crew are alive to trigger active sonar pulses from KRI Nanggala. This is because the seabed is reported to be a submarine crushing 700m deep where Nanggala was lost.

MANY MORE DETAILS TO COME