Vastergotland class

   In the late 1970s the Swedish navy began to consider building a class of patrol submarines to replace the Draken class boats built in the late 1950s and early 1960s, and to supplement the Sjoormen class built in the second half of the 1960s and eventually sold to Singapore as training boats in the second half of the 1990s. The result was the Vastergotland class, whose design was contracted to Kockums of Malmo during April 1978.

   The type was conceived with a single hull, X-type after control surfaces combining rudder and hydroplane functions, and a Pilkington Optronics CK 38 optronic search periscope enhanced with night vision capability. Four boats in the class were commissioned in the period 1987-90. They were constructed by Kockums on the basis of its own central section and bow and stern sections by Karlskrona varvet.

   Operations in the acoustically tricky shallow waters of the Baltic demanded special consideration of quietening features, and the boats are also coated with an anechoic layer to reduce their reflection of active sonar pulses. The torpedo tubes are all located in the bow, and comprise six 533-mm (21-in) tubes over three 400-mm (15.75-in) tubes. All the tubes are used for wire-guided torpedoes, the larger-diameter tubes firing swim-out FFV Type 613 passive-homing anti-ship weapons carrying a 240-kg warhead to a range of 20 km at 45 kts, and the smaller-diameter tubes firing FFV Type 431/451 active/passive-homing antisubmarine weapons carrying a 45-kg shaped-charge warhead to a range of 20 km at 25 kts.

   The last two boats are being lengthened by 10 m to allow the incorporation of a Stirling-cycle AIPS (Air-Independent Propulsion System) providing a submerged endurance of some 14 days. The first two boats may be passed to Denmark, which already has one Nacken class submarine from Sweden.