May 6, 2021: In March 2021 Indonesia put into service the KRI Alugoro, the first submarine built in Indonesia. This was also a first for Southeast Asia, where Indonesia has been developing and expanding its ability to build warshipsfor over a decade. The Alugoro was built with the assistance of South Korea, which delivered to two similar subs with the understanding that the third was built in Indonesia, a process that included the transfer of submarine construction technology and training Indonesian shipyard staff. This co-production deal with South Korea was first proposed 18 years ago. There were extended negotiations, lots of delays, agreement on design and cost (about $335 million each) and construction of the Alugoro began in 2016.The two subs built in South Korea entered service in 2017 and 2018. The Indonesian subs are called the Nagapasa class after the name of the first one. Indonesia ordered three more of these boats in 2019, all to be built in Indonesia. There is no start date yet for the three additional subs, which may be three more Nagapasas because the cost of the second three is similar to the first three. Indonesia may opt for or three of the similar but larger Son Won class subs South Korea began building in 2002. These are larger and more expensive, but also considered equal to the latest Chinese subs.

Indonesia was satisfied with performance of the first two Nagapasas and is apparently waiting to see if the Indonesian-built boat performs as well. So far that seems to be the case, as the Alugoro went through strenuous sea trials, as is common with all new submarines. Some Indonesian officers and crew from the first two South Korean built boats spent some time on the Alugoro during trials and found performance similar to what they experienced in the South Korean-built boats.

The Nagapasa boats are based on the South Korean Jang (or Chang) Bogo class subs, which South Korea had already built nine of. These subs were is an improved version of the German Type 209, but built in South Korea under license. The South Korean Navy put nine locally built Chang Bogos into service between 1993 and 2001. It is a proven design and that was a major selling point. The Nagapasas have improved sonar, radar and fire control equipment, similar to what South Korea is installing in new subs or older Jang Bogos that refurbishes its every ten years. These subs typically remain in service for about 30 years.

The Jang Bogos are 1,200-ton boats that are 55.9 meters (174 feet) long, have a top speed while submerged of 39 kilometers an hour, and a top surface speed of 20 kilometers an hour. Range is 20,900 kilometers at a surface speed of 7.4 kilometers an hour. Endurance is 50 days and the highly automated boat has a crew of only 31. The Nagapasas have berths for about 40 personnel indicating larger crews of planned use or carrying special operations troops for some reconnaissance missions. Armament is 14 torpedoes fired from eight 533mm (21 inch) tubes.

Since 2003, when Indonesia began looking for ways to expand its submarine force and replace two older (entered serviced in 1981) German subs, South Korea has been the leading candidate to supply the new subs. The first obstacle Indonesia ran into was the high cost of replacement boats. New subs can cost over half a billion dollars each, although Russia was offering better prices on new Kilos. But Indonesia had a bad experience with Russian subs back in the 1960s. The two German type U209 boats they bought in the 1980s as the Cakra class proved sturdy, effective and durable.

The Carkas are now old boats and one of them was lost at sea in April 2021. It was found after three days on the ocean floor 850 meters (2,700 feet) down. This is 350 meters deeper than the boat was designed to go. Keeping a diesel-electric sub in service past 40 years means the older boat will go to sea less often and be used mainly for training. This provides the more recently built boats with trained crews, rather than have each sub devote some of its time to ensuring that new crewmen are ready. It was found that the lost sub had more people on board than there should have been and may have been carrying out risky maneuvers, especially for an older boat, when the fatal malfunction occurred.

South Korea has an interest in what happened here because Indonesia made a deal with South Korea, which also operates German subs, to refurbish their German-built Cakras. The first one took two years, but in addition to replacing worn parts and checking for any hidden damage, lots of new navigation and weapons systems were installed and it returned to service in 2005. The boat that recent sunk completed its refurb in 2012. The two refurbished Cakras were good for at least another ten years. As the second Cakra was finishing its refurbishment in 2011, the Indonesian Navy finally obtained the money for new Nagapasas.

South Korea was eager to get the business, as South Korean shipyards are building more warships, including subs. Doing the Indonesian refurbs at a favorable price made South Korea a leading contender to supply Indonesia with new boats.