To strengthen its coastal patrol capabilities during the tumultuous Cold War years (1947-1991), the Royal Danish Navy invested in an indigenous submarine class which became the "Delfinen-class" (detailed elsewhere on this site). This group numbered four total boats of which all were designed, developed, and built in Denmark (the last of the group was funded by the United States to ease procurement costs). These boats operated from 1961 to 1990 and all have since been retired, marking the last Danish indigenously-originated submarines.
To bolster this undersea prowess at a time when the vaunted Soviet Navy was the enemy-of-the-day, the nation took on two more boats, these under the "Narhvalen-class" name and based in the West German "Type 205" coastal patrol attack submarines (detailed elsewhere on this site). The Danes secured a licensing deal with West German builder IKL to construct two of the Type 205 boats locally through the concern of Howaldtswerke at The Naval Dockyard of Copenhagen. The boats were appropriately modified to suit local Danish Navy requirements and ultimately led to HDMS Narhvalen and HDMS Nordkaperen being completed and commissioned into service.
The class was constructed from the period spanning 1965 to 1966 and launched in 1968-1969. HDMS Narhvalen (S320), the lead boat of the class, saw her keel laid down on February 16th, 1965. She was launched for evaluation and trials on September 10th, 1968 and ultimately commissioned for service on February 27th, 1970.
With a crew numbering just twenty-two (including four officers), the compact boat carried both passive and active sonar equipment and fielded a rather-traditional/conventional armament suite of 8 x 533mm (21") torpedo tubes. The boat could also be arranged to carry naval mines as needed. Internally, drive power stemmed from a twin marine diesel / single electric motor drive arrangement which provided for surfaced speeds of 12 knots and submerged speeds of 17 knots. 2 x Mercedes-Benz V12 diesel engines outputted 600 horsepower each for surfaced travel and 1 x SSW electric motor of 1,300 horsepower provided the needed power for submerged work. Range reached a maximum of 4,200 nautical miles. The hull was tested to a depth of 330 feet (100 meters).
When the Royal Danish Navy took on three ex-Kobben class boats from the Royal Norwegian Navy (these becoming the "Tumleren-class" in Royal Danish Navy service), it was decided to upgrade the Narhvalen-class boats to the same fighting standard and this work was undertaken from 1993 to 1995, resulting in an all-new, modernized propulsion scheme, new radar, a German sonar fit, French optics at the sail, and a British ESM suite.
With the loaning of the ex-Swedish submarine Nacken (becoming "Kronborg" in Royal Danish Navy service) in 2000, Narhvalen and her sister were relegated to second-line roles in Royal Danish Navy service for only a brief period, the former decommissioned in full on October 16th, 2003 and scrapped. Kronborg was used for an equally short amount of time, operating from 2001-2005 and returned to the Swedish Navy thereafter.