Fantome and her sister ships were constructed of an iron frame sheathed with teak and copper (hence 'composite').

A two-cylinder horizontal compound-expansion steam engine provided by Humphrys, Tennant & Co. powered an 11-foot (3.4 m) diameter screw.

Steam was provided by three cylindrical boilers working at 60 pounds per square inch (4.1 bar).

The Fantome class carried two 7-inch (180 mm) and two 64-pounder muzzle-loading rifles, all mounted on pivots.

Built at a time of great technological change in naval architecture, these composite sloops were obsolete before they were completed.