The sidewheel steamer was a transition ship between wooden sailing ships and steam-driven ironclads.
Sidewheelers had wooden masts and hulls, but the hull frames, boilers, and engines were made of iron.
To move through the water, sidewheelers used sails in strong wind and steam engines on calm days. The engines turned paddlewheels on the port and starboard sides. Steam power allowed these vessels to move without depending on the wind, like frigates.
Unfortunately, the paddlewheels were easy targets for enemies. Paddlewheels were soon replaced by underwater propellers which were harder to damage.