Sjoormen class

   The first of the modern type of submarines for the Swedish navy was the Sjoormen class designed in the early 1960s by Kockums, Malmo and built by that company (three units) and Karlskronavarvet (two units). The class comprised the Sjoormen, Sjolejonet, Sjohunden, Sjobjornen and Sjohasten. With an albacore type hull for speed and a twin-deck arrangement the class was extensively used in the relatively shallow Baltic, where its excellent maneuverability and silent-running capabilities greatly aided the Swedish navy's anti-submarine warfare operations.

   The control surface and hydroplane arrangements were the same as those fitted to the latter Swedish submarine classes, and it was these together with the hull design that allowed the optimum maneuverability characteristics to be used throughout the speed range, though they were more noticeable at the lower end: for example, a 360° turn could be achieved in five minutes within a 230-m diameter circle at a speed of 7 kts underwater. If the speed was increased to 15 kts the same turn would take only two and a half minutes, which meant the class could easily out-turn most of the Warsaw Pact anti-submarine escorts encountered in the Baltic, as well as most of the NATO escorts.

   Sjobjornen was modified and upgraded for tropical conditions 1996-97 and re-launched as Challenger on 26 September 1997, as one of four submarines of the Challenger class on order for the Republic of Singapore Navy. The other vessels comprise Centurion (ex-Sjoormen), Conqueror (ex-Sjolejonet) and Chieftain (ex-Sjohunden) and together form 171 Squadron. The weapons options for the reconditioned boats comprises a combination of FFV Type 613 anti-ship torpedoes (10 carried) and FFV Type 431 ASW torpedoes (four).