Challenger-class submarine

The "Challenger" class is one of the submarine classes of the Singapore Navy. They are extensively modernized versions of ex- submarines. "Challenger" and "Centurion" were retired in 2015.
History.
In 1995, the RSN acquired a "Challenger"-class vessel (formerly known as a from the Swedish Navy) and another three in 1997, making them Singapore's first underwater platforms. It is believed that the "Challenger" class were purchased to develop the required submarine operations expertise before selecting a modern class of submarines to replace them, since all the boats are over 50 years old.
Modernisation.
The "Challenger"-class submarines have undergone the Riken modernisation programme tailored to the specific operational conditions of the Singapore Navy. As the submarines were designed by the Swedish for operations in the Baltic Sea, various modifications were required to suit them 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.