Wild Swan and Penguin were re-engined after their first commission to match the better engines in the rest of the class. In the final installation, power was provided by three cylindrical boilers, which supplied steam at  to a two-cylinder horizontal compound-expansion steam engine driving a single  screw.
Wild Swan and Penguin were redesigned after their initial assignment to match the more powerful engines in the rest of their class. In the final configuration, power was generated by three cylindrical boilers that provided steam to a two-cylinder horizontal compound-expansion steam engine driving a single screw.