HNLMS O 21 was a submarine of the Royal Netherlands Navy that served during World War II. Commissioned in 1939, O 21 was part of the O 20-class submarines, designed for operations in the Dutch East Indies. The submarine had a length of 77.7 meters and a top speed of 19 knots when submerged. During the war, O 21 conducted patrols in the Java Sea and Indian Ocean, engaging in various missions against Japanese forces. Notably, the submarine successfully torpedoed and sank the Japanese cruiser Ashigara in 1944. In May 1945, O 21 was part of a joint British-Dutch operation near Singapore, where it sank a Japanese tanker before being attacked by a Japanese aircraft and suffering damage. Post-war, the submarine was used for mine clearing operations in the Dutch East Indies. In 1951, O 21 was decommissioned and eventually sold for scrap in 1962. Today, remnants of the submarine can be found in various maritime museums in the Netherlands. Overall, HNLMS O 21 played a significant role in naval operations during World War II, showcasing the capabilities and contributions of Dutch submarines in the conflict. Its missions and engagements in the East Indies and Indian Ocean highlight the strategic importance of submarines in naval warfare during this period.

This description has been generated using GPT-3.5-TURBO based on the Vessel's wikidata information and then modified by ShipIndex.org staff.