The Jang Bogo-class submarine (Hangul: 장보고급 잠수함, Hanja: 張保皐級潛水艦) or KSS-I (Korean Submarine-I) is a variant of the Type 209 diesel-electric attack submarine initially developed by Howaldtswerke-Deutsche Werft (HDW) of Germany, intended for service with the South Korean Navy and Indonesian Navy.

The South Korean Jang Bogo-class submarines, originally based on Type 209/1200, had reportedly been heavily upgraded from a time early in the 21st century,[7] which if properly undertaken was supposed to include domestic hull stretch augmentation from 1,200 tons to 1,400 tons, and installment of domestically developed Torpedo Acoustic Counter Measures (TACM).

[20][21] LIG Nex1 began producing TACM for unspecified submarine types of the ROKN as well, which finished development in 2000.

[17] The Jang Bogo class offered to Indonesia will already be in stretched and augmented forms including guided missile-launching capabilities and a surface displacement of 1400 tons, quite similar to the original plan to upgrade the existing Jang Bogo-class submarines of ROKN to similar specifications.

[3] A science documentary by EBS reported that Jang Bogo-class submarines will undergo major generational overhaul and refit every eight to twelve years.

[24][25] In December 2011, DSME won a contract to build 3 1,400-ton Chang Bogo-class submarines for Indonesia at a cost of $1.07 billion.

Indonesia was also offered two license built Type 209 submarines manufactured by a group of Turkish (SSM - Undersecretariat for Defense Industries) and German companies (HDW/ThyssenKrupp), a deal reported to be valued at $1 billion.

[36] In 2019, South Korea signed another contract worth US$1.02 billion to sell three 1,400-ton submarines to Indonesia[4] and would be supported through a loan agreement.