South Korean Sohn Wonyil class submarine Sindolseok visits Guam.

According to information published by the US DoD on September 24, 2022, the Republic of Korea Sohn Wonyil class diesel-electric submarine ROKS SINDOLSEOK (SS 082) sails into Apra Harbor towards Naval Base Guam.
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South Korean Sohn Wonyil class submarine Sindolseok (Picture source: US DoD)

Type 214 is a diesel-electric submarine developed by Howaldtswerke-Deutsche Werft GmbH (HDW).[2] It features diesel propulsion with an air-independent propulsion (AIP) system using Siemens polymer electrolyte membrane (PEM) hydrogen fuel cells.

The class is exclusively designed for export market. The submarine class combines the design principles of the Type 209 family and the features of the Type 212A submarines.

However, as an export design, it lacks some of the classified technologies of the smaller Type 212, the most important of which is probably the non-magnetic steel hull, which makes the Type 212 submarine difficult to detect using a magnetic anomaly detector.

The South Korean Son Won-Il U214-class submarine is equipped with a SPHINX-D Radar System supplied by Thales Defence Deutschland GmbH. It uses an additional pulse transmitter in the top of the mast.

The combination of high power pulse radar and a very low power LPI transmitter is very effective for submarines. During surface operations, the boat sails with an open pulse fingerprint for ESM systems, but within a secret mission the operator switches to LPI mode.

The boat remains invisible to others. Total of 9 are planned and 8 are in active duty. South Korea ordered its first three KSS-II/ Type 214 boats in 2000, which were assembled by Hyundai Heavy Industries. The Batch 2 order will add six more submarines to the Navy, to be built by Daewoo Shipbuilding & Marine Engineering.

Naval Base Guam is a strategic U.S. naval base located on Apra Harbor and occupying the Orote Peninsula. In 2009, it was combined with Andersen Air Force Base to form Joint Region Marianas, which is a Navy-controlled joint base.