Description:
Type A-11/Sjoormen, Sea Serpent in English, is a class of diesel-electric attack submarines built by Kockums for the Royal Swedish Navy in the late 1960s. The class consisted of five boats. They were equipped with four 533mm and two 400mm torpedo tubes. Its innovative design introduced modern hydrodynamic hull shape, one-man maneuvering system and the X-rudder configuration giving the submarine outstanding maneuvering characteristics.
In the 1990s the Royal Singapore Navy purchased these ships which were withdrawn from service in the Swedish Navy. Within 1996/1997 Kockums refurbished these boats to operate in tropical climates and following Singapore's Navy specific operational conditions. Finally, were transferred to its new owner between 2000 and 2004. Singapore's Sjoormen submarines were designated the Challenger class.
Specifications Accommodation: Crew 28
Singapore / 4 
Sweden / 5