The missing submarine KRI Nanggala-402, which has 53 people on board, lost contact during training maneuvers in the north of the island of Bali, in Indonesiaat 3 am (local time) on Wednesday (21).

Contact with the German submersible manufactured in 1977 and modernized in 2012 was lost after he received authorization to dive in deeper waters. "We know the area, but it is quite deep," Julius Widjojono, the first Indonesian navy admiral, told AFP news agency.

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Six ships of war, a helicopter and 400 people are involved in the searches with help from Singapore, Malaysia, Australia, the United States, France and Germany. “Reserves of oxygen the submarine during a power outage is 72 hours, ”Yudo Margono, commander of the Indonesian General Staff, told the press.

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According to the Navy, an oil spill found near the site the submarine dived in could point to damage to the fuel tank or could also be a signal from the crew.

Australian Defense Minister Peter Dutton said the information increased "the fear of a terrible tragedy". "It is possible that a power outage occurred, which left the submarine out of control and prevented the launch of emergency measures, sinking at 600 or 700 meters," explained a spokesman for the Indonesian Navy.

"If he sank 700 meters, there is a good chance that he broke," French Vice Admiral Antoine Beausssant told the France Presse news agency.

But why is it so hard to find a missing submarine?

It is important to remember that military submarines are built with “stealth” technology to cross the oceans in the most undetectable way possible. They emit almost no noise or heat and reflect radar and sonar impulses as little as possible.

Aerodynamics are very important because the better the displacement of the submarine, the lower the noise and heat emission from the engine.

Currently, in military submarines practically only non-magnetic materials are used, such as stainless steel or titanium. This has to do with the fact that many underwater mines are equipped with magnetic detonators. If a ship's hull passes too close, they explode.

A suitable coating can absorb much of the sonar signal. Thus, on the screen, the submarine can appear only as a mound of scattered mud.

KRI Nanggala-402 has undergone two-year renovation

The KRI Nanggala-402 was manufactured in 1977, but underwent a complete overhaul for two years in South Korea. In February 2012 it was handed over to the Indonesian government with much of its upper structure replaced. Its armament, sonar, radar, combat control and propulsion systems have been updated.

The submarine now has a safe diving depth increased to 257 meters (843 feet) and a maximum speed increased from 21,5 knots (39,8 km / h) to 25 knots (46 km / h). The submersible also became capable of firing four torpedoes simultaneously at four different targets and launching anti-ship missiles.

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