Nacken class

    Since World War II Sweden has placed considerable emphasis on the possession of a small but highly capable force of conventional submarines as a key element in the preservation of its long coastline against the incursions of other nations surface and underwater forces for the purposes of reconnaissance and/or aggression. The Swedish navy's first post-war submarines were the six boats of the Hajen class, built during the 1950s on the basis of the German Type XXI class design: the design data were derived from the U-3503, which its crew had scuttled off Goteborg on 8 May 1945 and which the Swedes subsequently salvaged.

   From 1956 the Swedes followed with six examples of the indigenously designed Draken class, and in 1961 the Swedish government approved plans for five more advanced submarines of the Type A12 or Sjoormen class. This latter introduced a teardrop-shaped hull with two decks and X-configured stern planes.

   The Swedish navy considers the effective live of its conventional submarines to be something in the order of 10 years, and in the early 1970s raised the matter of a class to succeed the Sjoormen class from a time later in the same decade. The Swedish government have its approval to the request in 1972, and the Swedish defense ministry was therefore able to contract in March 1973 with Kockums of Malmo (two boat) for the three Type A14 of Nacken-class diesel-electric submarines. The boats were all laid down in 1976 and launched between April 1978 and August 1979 for commissioning between April 1980 and June 1981 as the Nacken, Neptun and Najad.

   The Baltic, which is the primary operational theatre for Sweden's submarine arm, is shallow, so the diving depth of the Nacken-class boats was fixed at some 150 m (500 ft). The boats were based on the same type of teardrop-shaped two-deck hull as the Sjoormen class, and were completed with Kollmorgen periscopes from the US as well as the Data Saab NEDPS combined ship control and action information system.

   In 1987-88 the Nacken was lengthened by 8 m (26 ft 3 in) to allow the installation of a neutrally buoyant section containing two liquid-oxygen tanks, two United Stirling Type V4-275 closed-cycle engines and the relevant control system, this air-independent propulsion arrangement boosting the submerged endurance to 14 days and in effect making the boat a true submarine rather than just an advanced submersible.

   From the early 1990s the boats were upgraded to a partial Vastergotland class standard in their electronics. But were discarded from a time later in the same decade. The sole surviving boat is the Kronborg of the Danish navy, which was the Nacken until transferred in August 2001, after a refit by Kockums, under a lease to buy or return (in 2005).

   The boat is armed with wire-guided torpedoes, the 533 mm Type 613 passive anti-ship weapons attaining 45 kts (83 km/h) over a range of 20 km, and the 400 mm Type 431 active/passive anti-submarine weapons having a speed of 25 kts (46 km/h) over the same range.