Technical review about the lost submarine KRI Nanggala 402 of Indonesian navy.

On April 21, 2021, the Indonesian navy has declared missing the KRI Nanggala (402). Three days later, on 24 April, debris from the submarine was found on the surface, and the navy declared Nanggala sunk. The KRI Nanggala is one of the two Cakra-class Type 209/1300 diesel-electric attack submarines in service with the Indonesian Navy.
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The Indonesian submarine KRI Nanggala (402) participates in a photo exercise in the Java Sea during Cooperation Afloat Readiness and Training (CARAT) Indonesia 2015. (Picture source Wikimedia)

The Cakra is a class of two Type 209/1300 Diesel-electric attack submarines developed by the German company Howaldtswerke-Deutsche Werft that were bought and commissioned in the 1980s by the Indonesian Navy. The Type 209 submarine and variants are operated by 13 countries including Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Egypt, India, Indonesia, Peru, South Korea, South Africa, Turkey, Venezuela.

The Indonesian navy operates two classes of Type 209 submarines, the Cakra-class Type 209/1300 vessels and the Nagapasa-class Type 209/1400. The Cakra-class submarines were ordered on 2 April 1977, designed by German company Ingenieurkontor Lübeck of Lübeck, constructed by Howaldtswerke-Deutsche Werft of Kiel, and sold by Ferrostaal of Essen.

The Cakra-class is a diesel/electric powered submarine that includes four MTU 12V493 AZ80 GA31L diesel engines rated at 1.8 MW (2,400 hp), four Siemens alternators rated at 2,300 hp (1.7 MW), and one Siemens motor rated at 3.4 MW (4,600 hp) driving a single shaft. The submarine can reach a surfaced speed of 11 knots (20 km/h) and 21.5 knots (39.8 km/h) in submerged conditions. It has a maximum cruising range of 8,200 (15,200 km) nautical miles at 8 knots (15 km/h).

The Cakra-class has a length of 59.5 m, a beam of 6.2 m, and a draft of 5.4 m. It has a maximum diving depth of 240 m. The submarine has a crew of 33 people.

The Cakra-class submarine is equipped with a Thomson-CSF Calypso surface search radar that operates at I-band. The sonar suite includes an Atlas Elektronik CSU 3-2 hull-mounted passive and active search-and-attack sonar and flank sonar arrays. The submarine is armed with eight 533 mm torpedo tubes and can carry up to 14 AEG SUT torpedoes, a German 21-inch heavyweight wire-guided torpedo produced by Atlas Elektronik which entered service in 1967.