[2] Designed by Nathaniel Barnaby,[1] the Royal Navy Director of Naval Construction, the hull was of composite construction; that is, iron keel, frames, stem and stern posts with wooden planking.

This class of composite sloops was unique in having an internal steel deck over the machinery and magazines for protection.

Propulsion was provided by a horizontal compound expansion of 1,400 indicated horsepower (1,044 kW) driving a single screw.

The class was designed with two 6-inch/100-pounder (81cwt) breech loaders and ten 5-inch/50-pounder (38cwt) breech loaders, plus a single light gun and four (or more) machine guns.

[1] Heroine, Hyacinth and Royalist were built with eight 6-inch/100-pounder (81cwt) breech loaders in place of the 5-inch/6-inch mixture, and Satellite was converted to the same fit.