User:DeHooMin/Sandbox/Sjöormen class submarine

The Sjöormen class were a group of submarines built for the Swedish Navy in the late 1960s. They had a teardrop shape and were capable of diving to 150m. At the time of their deployment they were regarded as one of the most advanced non-nuclear submarine-classes in the world, incorporating many new features including x-rudder and anechoic tiles. Both speed and underwater endurance was at this time very high for a conventional submarine. The ships were retired by Sweden in the early 1990s.

Sale to Singapore
Four of the ships were sold to Singapore in 1996 and modernised in the late 1990s by Kockums. Various modifications were required to suit the boats to tropical waters. A comprehensive tropicalisation programme was carried out for all four submarines, which involved installing air conditioning, marine growth protection systems and corrosion-resistant piping. , they are currently in service with the Republic of Singapore Navy as the Challenger class.